# What is the Sandbox?

This "Sandbox" is a place where Code Golf users can get feedback on prospective challenges they wish to post to the main page. This is useful because writing a clear and fully specified challenge on the first try can be difficult. There is a much better chance of your challenge being well received if you post it in the Sandbox first.

See the Sandbox FAQ for more information on how to use the Sandbox.

## Get the Sandbox Viewer to view the sandbox more easily

To add an inline tag to a proposal use shortcut link syntax with a prefix: [tag:king-of-the-hill]

• How are tags added to questions? – guest271314 Jan 9 at 7:51
• @guest271314 You can use this markup to create a tag in a draft: [tag:code-golf] – DJMcMayhem Aug 29 at 15:19
• Why no featured anymore? Can't we have it auto-added or something? – JL2210 Sep 26 at 15:57
• @JL2210 We now have a permanent info box that links to the Sandbox, so the featured tag isn't necessary – caird coinheringaahing Sep 29 at 13:43

# A Fine-Grained Mesh

If you've used Matlab before, it's highly likely that you've heard of meshgrid. It's a function that has since mostly been obsoleted by broadcasting, but it still has its uses sometimes.

The function itself is relatively simple. Given two vectors x and y of length m and n, create two 2-dimensional matrices X and Y both with m columns and n rows such that:

1. Any row of X is a copy of x
2. Any column of Y is a copy of y

But typing out meshgrid(x,y) takes so long, you know? I'd like to be more efficient with my coding. Your job is to reimplement this function in the fewest bytes possible.

Standard loopholes disallowed.

• This is a classical case of do X without Y which is discouraged. The reason is that some languages might have something similar that is not quite equal, and then it is always the question: Where do you draw the line? I recommend against banning built ins. – flawr Dec 10 '17 at 19:46
• @flawr I removed that as a requirement. – Steven H. Dec 11 '17 at 19:58
• You could add "builtins that compute this are allowed but a second implementation without using that builtin are strongly encouraged" – Giuseppe Dec 11 '17 at 20:34
• what types are x and y? Int, float, char, ...? – Giuseppe Dec 11 '17 at 20:36
• x and y can be any vector-like type. Lists, arrays, actual vectors... – Steven H. Dec 12 '17 at 2:30

# Flit - a simple board game for bots

I've made a human playable version of this game with a simple strategy to give an idea of how the game plays out. You can play it before or after reading the rules here - picking up the rules intuitively adds an extra challenge...

If playing this gives any idea about whether the KotH version would be better with 2, 4, or more players per game, or any other subtle adjustments that would help, please let me know.

Note: adjacency is vertical or horizontal - for this game there are no diagonal neighbours.

## Overview

The board is a square grid. Each bot starts with 2 pieces of their colour, and gains more pieces by converting neutral pieces that appear from time to time. The objective is to end up with more pieces than your opponents.

Each turn, one bot moves. It chooses one of its pieces and moves it to be next to another of its pieces. There is no limit to the distance a piece can move in a single step, provided it lands next to a piece of the same colour.

### Neutral pieces

There are initially zero neutral pieces.

A new neutral piece can appear at any time, regardless of whether there are already neutral pieces unconverted. A neutral piece will only appear on an empty square that has 4 empty neighbours, to prevent it being instantly converted.

If a neutral piece is adjacent to another piece, it is converted - it becomes the colour of that piece. A neutral piece can only ever be adjacent to a single other piece - it will be instantly converted before any other bot has a chance to move next to it.

### Moving

A move is specified by an origin square and a destination square. It is a valid move if the origin square contains a piece of the bot's colour, and the destination square is empty and is adjacent to at least one piece of the bot's colour. Note that the piece being moved cannot also be the piece adjacent to the destination square (a piece cannot simply move next to its own previous position). Two distinct pieces are required - one to be moved, and one to be adjacent to the destination.

[Not moving is a valid move, and is indicated by specifying the same coordinates for origin square and destination square. not sure about this rule] Not supplying a move within the time limit also results in not moving, but repeatedly exceeding the time limit will lead to the bot losing the opportunity to make further moves.

### Communication

The board information will not be supplied each turn. Instead the bot must keep track of the board state itself. Each time a change is made a message will be sent to all bots describing the change. If a bot chooses not to move, the non-move will not be broadcast.

The board starts empty. The initial two pieces for each bot will be broadcast to all bots, then the first bot will be sent a request for a move, to which it must respond within the time limit. Any response sent after the time limit expires will be discarded (any waiting input will be read and discarded before the next request for a move is sent to that bot).

Bots will therefore have complete information about the board state at all times.

# Specification

Available: An available square is an empty square that has 4 empty neighbours

### Players

There are 4 bots competing in each game. Bots are numbered 1 to 4 and take turns in that fixed order.

### Board

The board is a 32 by 32 square grid. It wraps toroidally - every square has 4 neighbours. The board has no boundaries - no edges or corners to give an advantage.

### Initial state

For each bot, one piece will be placed on a square chosen uniformly from the available squares. After all first pieces have been placed, a second piece will be placed for each bot in the same way. The initial state contains no neutral pieces.

Each turn one bot will move. After that move has been made, the addition of a new neutral piece will be considered. A square will be selected at random. If that square is available then a neutral piece will be placed on it with probability 1/16. If the square is unavailable then play continues - a second square will not be selected. [This differs from the human playable version linked above: there a list is kept of all available squares and a neutral piece is placed on one of those with probability 1/6 each turn - I now prefer this approach so the rate of new neutral pieces does not slow in the end game]

### Bot STDIN

All received messages will be terminated by a newline. Each bot will receive messages of two types: an update or a move request

Update:

x y c

where (x, y) is the square to be updated, and c is the new colour (which may be 0 for empty, 1, 2, 3 or 4 for a bot colour, or 5 for neutral).

Move request:

M

where M is the literal string "M" and indicates that a move is required.

### Bot STDOUT

The response must be terminated by a newline. A bot responds with a move in the following format:

x0 y0 x1 y1

where (x0, y0) is the origin square, and (x1, y1) is the destination square.

If origin and destination are identical, no move will be made. This is valid and does not lead to the bot being penalised. The bot will only be penalised if it fails to respond within the time limit.

### Time limit

The time limit is 50ms. If a bot exceeds the time limit on 5 consecutive turns then it will no longer be prompted for moves. That bot will be frozen for the rest of the game.

### Winning criterion

The winner is the bot with the most pieces when the game ends. There is no reward for second place. If two bots tie for first place, neither is rewarded.

The game ends when one of the following conditions is met:

• the total number of turns taken exceeds 32,768 (8,192 per bot)
• all 4 bots choose not to move consecutively
• one bot has too many pieces to catch up with

Too many pieces to catch up with is defined as follows:

• A, B and C are the numbers of pieces of the other 3 bots.
• D is the number of pieces of the bot in question.
• N is the number of neutral pieces.
• E is the number of empty squares.
• P is the number of potential neutral pieces. P = N + E - 4
• M is the maximum number of pieces attainable by A, B or C.
• M = Max(A+P, B+P, C+P)
• If D > M then the bot has too many pieces to catch up with.

I've tried to make this game as simple as possible, while still having non-trivial dynamics.

• Time limit could be abused - the bot is allowed to just take its sweet time for 4 turns straight, followed by a reset... How about average time? – Alion Feb 18 '18 at 12:40
• Ah good point. I'll probably go with average time per move after an arbitrary 10 seconds to allow for high variance early on. – trichoplax Feb 18 '18 at 12:57
• First player is at a very slight, systemic disadvantage. He's the only one that cannot see a neutral piece on his first turn. Piece spawning should probably happen before each player makes a move, instead of after. – Alion Feb 20 '18 at 14:58
• Oh good point. That small difference is definitely relevant. Neutral pieces before rather than after a move sounds good. – trichoplax Feb 20 '18 at 17:18

# Musical Washing Machine

I have a washing machine with a knob and several buttons. The knob selects the type of laundry and the buttons cycle through water temperature, etc. options. When pressed, these each create a musical note. There are five musical notes that can be made, in this ascending order: F A C D E

knob (K)
When 360ed: play D and reset all other buttons
wash temp (T)
1st press (cool -> warm): A
2nd press (warm -> hot): F
3rd press (hot -> cold): E
4th press (cold -> cool): C
(repeat)
spin speed (S)
1st press (medium -> max extract): F
2nd press (max extract -> no spin): E
3rd press (no spin -> medium): A
(repeat)
soil level (L)
1st press (medium -> heavy): A
2nd press (heavy -> extra heavy): F
3rd press (extra heavy -> light): E
4th press (light -> medium): C
(repeat)


# The Challenge

Given a series of notes, determine if if can be played on my washing machine, and, if so, output the series of moves to generate it.

I/O coming soon to a washing machine near you

• As a side note, there is a washing machine that plays the New Zealand Athem – MickyT Aug 27 '15 at 21:02
• I think I understand, but it looks a bit confusing. Maybe you should give an example with an explanation. – Beefster Feb 9 '18 at 17:18

# Make a Sierpinski triangle

Your challenge is to output a n-th order right-angle Sierpinski triangle, similar to this (third-order):

#
# #
#   #
# # # #
#       #
# #     # #
#   #   #   #
# # # # # # # #


### Input:

A number, n, and a character (in this example '#');

### Output:

A 2**n (two to the n) line Sierpinski triangle, made of the given character. You could consider it a two-state cellular automaton: the cells are separated by a single spaaace; if it is on, it contains the given character; Otherwise is contains a spaaace.

### Examples:

in:

0 *


out:

*


explanation:

2**0=1

in:

1 *


out:

*
* *


in:

2 *


out:

*
* *
*   *
* * * *


## Winner:

this is codegolf so the winner is the answer with the least bytes. (NOTE: might add something tho do with triangles of the same character.)

### Hint:

it might be helpful to know that the n-th line contains the previous line xor that line shifted right by one cell (x^(x>>1)).

• Welcome to PPCG and thanks for using the sandbox! There is a challenge to draw an Sierpinski Triangle which is broad enough to allow your format, so the challenge might be considered a duplicate. Then again I think the old challenge is no longer up to the current site standards and should probably be closed ... – Laikoni Mar 10 '18 at 10:08
• This is also close enough to Generate Pascal's triangle that by the standards of this site (can answers be copied with trivial modifications?) I would consider it a duplicate. – Peter Taylor Mar 10 '18 at 19:42

# -(-(--x)--))> Code Kebabs! <-(-(--x)--))

Your goal is to parse Code Kebabs, they look like this:

-x--> 8
2 <-(-(--x)--))
-x-x-x--> -10
--x> 255


A Code Kebab is made up of 3 parts, the stick, the tip (< and >), and the stand (the number compared by)

stick tip stand
--x-- >   -5


### The stick

The stick contains 4 operators, and the variable (x) The operators are listed here, in order of precedence:

1. ( ... ) | Brackets. They are the "veggies" on a code kebab. Everything inside them runs before the rest of the kebab, with the last, deepest pair going first. Brackets can be nested.

2. v-- | Suffix decrementation. This is one of the 4 parts of the stick, and decrements the value supplied to it by one.

3. v-v | Subtraction. This is the 2nd part of the stick, and subtracts the two values.

4. --x | Prefix decrementation. This is the 3rd part of the stick, and decrements the value supplied to it by one.

5. -v | Negation. This is the 4th and final part of the stick, and inverts the value supplied.

Each operator returns it's result, and can be used as input for other operators.

### The Tip

The tip is one of two symbols: < or > When the tip is <, the stand must be left of it, with the tip being left of the stick. When it is >, the stand is to it's right, with the tip being on the right of the stick.

### The Stand

The stand is any integer. That's all there really is to say about it.

### Execution of the kebab

You can't execute a kebab without eating it!

Kebabs are executed in a loop until their condition (The result of the stick being less than the stand's value) is fulfilled. When execution is finished, the variable (x) is set to the result of the stick, X is printed, and execution resumes again unless the condition is fulfilled.

When execution starts for the first time, X is set to 10 beforehand.

### TODO

• Clear a few things up.

• Make the description of execution a bit clearer?

• You should describe the difference between pre and post decrement. – Pavel Apr 30 '18 at 21:22
• Also, how are the input variables initialized? – Pavel Apr 30 '18 at 21:22
• A test case that has something like -x--5 to force parsing it as a subtraction and unary negation, rather than post-decrement x, would be very good. – AdmBorkBork May 1 '18 at 13:02
• @AdmBorkBork Numbers aren't mentioned as a requirement for parsing, so -x--x would probably work better. But yea, good idea. – moonheart08 May 1 '18 at 13:48
• @Pavel The input variable X is set to 10 beforehand, as mentioned in The execution of the kebab – moonheart08 May 1 '18 at 13:51
• Is this correct? And if not, where is my flaw? The input is the Code Kebab (i.e. -x--> 8) with x=10 by default, and the output is the x once it fulfills the Kebab check. So for -x--> 8 with x=10 as start, it will do x-- first (so it becomes x=9), and then the -x negation (so it becomes x=-9), and then checks it with the tip (-9 > 8). This is false, so it continues with x now being -9? So then x-- again (x=-10), then -x again (x=10), and then the check again (10 > 8). Which is true, so it outputs 10 as result? I have the feeling I misunderstand it a bit.. – Kevin Cruijssen May 2 '18 at 11:08
• Also, why is suffix decrementation before prefix? In most languages (Java, JS, C, etc.) it's usually the other way around. – Kevin Cruijssen May 2 '18 at 11:10
• And one more question, is something like ---x (negation & prefix decrementation), or x---x (suffix decrementation & subtraction) a possible valid input? Or would these always be surrounded by parenthesis (---x would be -(--x) instead; x---x would be (x--)-x or x-(--x) instead). – Kevin Cruijssen May 2 '18 at 11:14

# Nearest neighbors in a square lattice

## Premise

Consider an infinite 2D square lattice. We can choose one point as the origin and label each point with a pair of integers that corresponds to points on the Euclidean plane:

Now consider the point at the origin, $(0,0)$. The set of lattice points closes to the origin (but not including the origin) is $\{(1,0),(0,1),(-1,0),(0,-1)\}$. We will call this set the $1$st nearest neighbors. The set of lattice points closest to the origin but not including the $1$st nearest neighbors is $\{(1,1),(-1,1),(-1,-1),(1,-1)\}$. We call this set the $2$nd nearest neighbors

Now we can define the $k$-th nearest neighbors as the set of points closest to the origin and not included in the union of the set of $n$-th nearest neighbors for $n\in\{1,2,...k-1\}$.

Define the sequence $NN(k)$ as the length of the set of $k$-th nearest neighbors.

Given $k$, compute $NN(k)$. This is A105352 on OEIS without the first element.

## Rules

• You may use 0- or 1- based indexing.
• Given $k$, you may either output the first $k$ elements of the sequence or the $k$-th element.
• You may alternatively take no input and output the sequence indefinitely.
• Standard loopholes disallowed.

Here are some 1-indexed test cases:

n   NN(k)
1   4
8   8
9   4
10  8
38  16
52  8
80  8
121 24
145 12

• – Mr. Xcoder Sep 13 '18 at 20:47
• @Mr.Xcoder Thanks – dylnan Sep 13 '18 at 20:58
• Could you allow the infinite sequence $\{NN(1),NN(2),NN(3),\ldots\}$ as output (with no input)? – Delfad0r Sep 15 '18 at 8:34
• @Delfad0r Sure. – dylnan Sep 15 '18 at 16:33
• Very related. Just filter out zeroes. – user202729 Sep 15 '18 at 16:38
• @user202729 Do you think it's a dupe? – dylnan Sep 15 '18 at 17:06
• @dylnan I don't know... – user202729 Sep 17 '18 at 13:08
• IMO it's a dupe: adding a loop and an if test is a pretty trivial modification. – Peter Taylor Sep 17 '18 at 14:34

## Breaking into 3 Palindromes:

As discussed here and here, every positive integer can be written as the sum of 3 palindrome integers. Given a number "n", output these integers.

## Challenge

• This is a code golf challenge. The shortest functional solution wins.
• The input number "n" will be any integer greater than 0 but less than 1,000,000,000.
• The three output numbers must be palindromes. Their sum must be "n".
• A palindrome number is a number which is the same forwards as backwards. It can have any number of digits.
• To make this easier, I will allow positive or negative palindrome integers.
• Output and input can be formatted in any what that is convenient as long as it can be readily understood.

## Examples

input: 5
output: 0,0,5

input: 1234
output: 1001,222,11

input: 3141592
output: 2200022,926629,14941

• This is actually a very interesting problem. The paper which proved that this would work for any base lists 40 different algorithms that are used to find these values depending on the value of "n". I suppose there should be a requirement to solve this in a reasonable about of time to avoid brute force but I don't know how I should phrase that. – kaine Sep 17 '18 at 21:18
• It's up to you, but time limit requires a particular computer to test the solutions on. – user202729 Sep 18 '18 at 1:18
• Maybe it would be a good idea to link that paper in the challenge. Also, I tried to bruteforce in 05AB1E, and the 1234 case already times out after 60 sec, so I won't even have to try 3141592.. It barely doesn't make it within the 60 sec, but does output most of the possible outputs. Maybe make this a [fastest-code] challenge instead of code-golf, so the goal is to solve it as fast as possible. Alternatively [fastest-algorithm] could be used as well, but usually when someone find one, others will copy it. – Kevin Cruijssen Sep 18 '18 at 6:41
• Honestly, i don't think i am comfortable managing a fastest-algorithm challenge due to my own limited skill. I'm a pretty amateur programmer so if someone uses languages, libraries, etc. I'm unfamiliar with I won't be able to fairly judge them. This idea though (complicated but sounds simple) seems great for one of these challenges. – kaine Sep 18 '18 at 13:04
• Would it be feasible to require the code to run within 20 minutes on Ideone? Is that linked to my computer's abilities? – kaine Sep 20 '18 at 13:39
• I think if you keep this at base 10 (decimal only) it's not so bad. – ouflak Sep 21 '18 at 12:59
• @ouflak I had no intention of leaving base 10. I'm really liking the Ideone idea but am not sure if people would be ok with that. – kaine Sep 21 '18 at 18:51
• rnta.eu/cgi-bin/three_palindromes/pal3.py and somethingorotherwhatever.com/sum-of-3-palindromes The speeds for these are bad at all. One in python the other in Javascript. I'm doing a C++ version (completely ungolfed) as I'm at a bit of a lull at the moment. It's just a translation of the Javascript code with some tweaks. I'll post a link to that as well. I would forget the timings and go with the straight up challenge. – ouflak Sep 26 '18 at 9:22
• I've done this up in non-golfed C++. Anybody know a site where I can put this online where people can run it? It's big, but fast. – ouflak Oct 3 '18 at 15:24
• The non-golfed C++ is 36 kbytes. Maybe limiting this to just the 4 digit case might be OK. I might try that in LUA and see what it looks like. This is such a great idea. Unfortunate that the algorithms are so lengthy. – ouflak Oct 8 '18 at 13:56
• @ouflak, the fact that the algorithms are lengthy is why I thought this would make a good challenge. It is ripe for optimization. I'm worried about posting this challenge though as I'm sure there are many algorithms that will give an answer eventually but are so slow they defeat the purpose of the challenge. – kaine Oct 8 '18 at 14:29
• Ok, I've sorted out a much shorter algorithm in LUA for the three digit case, un-golfed. repl.it/repls/AchingEnchantedHack. This has given me an idea for how to sort out the general case, which I think now actually might not be so bad. – ouflak Oct 9 '18 at 7:43
• Here is a solution that should work for any sized number. This is brutally un-golfed LUA. I haven't even taken the opportunity to use a recursive function where it obviously would apply. For 5 digit numbers and smaller, it's pretty quick, easily less than a second. For 6 digit numbers and above, it depends on how soon it finds the first set of palindromes. I had one number (390081) take a good five minutes on the test site. I'm sure it would be quicker on my machine. I'd like to think there are places for optimization for speed (as well as golfing). repl.it/repls/BlondWaryShareware – ouflak Oct 9 '18 at 11:59
• Just one other comment on your constraints, I wouldn't allow negative palindromes as I'm not convinced this makes it 'easier'. Should I start golfing this thing? ;) – ouflak Oct 9 '18 at 12:10
• @ouflak you can probably wait until i post it as a real question but your enthusiasm definitely implies I need to. – kaine Oct 9 '18 at 12:50

# Classical construction golf: Wernick's list No. 47 proof-golfgeometry

## Background

Compass-and-straightedge construction, a.k.a. classical construction, is the construction of lengths, angles, and other geometric figures using only an idealized ruler and compass. A ruler can only be used to draw a straight line passing through two given points; a compass can only be used to draw a circle with two given points (a center, and a point on the circle).

All compass and straightedge constructions consist of repeated application of five basic constructions using the points, lines and circles that have already been constructed. These are:

• Creating the line through two existing points
• Creating the circle through one point, with another point as the center
• Creating the point which is the intersection of two existing, non-parallel lines
• Creating the one or two points in the intersection of a line and a circle (if they intersect)
• Creating the one or two points in the intersection of two circles (if they intersect).

In addition to these listed on Wikipedia, we have the sixth basic construction:

• Creating an arbitrary point on the plane, possibly with a constraint:
• On a line ("line" includes straight lines and circles)
• Not on a line
• On a closed or open part of a line, bounded by existing points on it
• Inside a closed or open region, bounded by existing lines

In any geometric problem, we have an initial set of symbols (points and lines), an algorithm, and some results. From this perspective, geometry is equivalent to an axiomatic algebra, replacing its elements by symbols.

This is the basis of the new kind of : classical construction golf.

## Challenge

Wernick's list is a collection of construction problems. The common objective is to recover the three vertices of a triangle, given three of its 16 characteristic points. They include:

• $$\A, B, C, O/extract_tex]: three vertices and circumcenter, • $$\M_a, M_b, M_c, G\$$: the side midpoints and centroid, • $$\H_a, H_b, H_c, H\$$: three feet of altitudes and orthocenter, • $$\T_a, T_b, T_c, I\$$: three feet of internal angle bisectors and incenter. Out of the 139 problems, some are solvable by construction, but some are not. The problem we'll tackle here is problem 47, where the given points are: • $$\A\$$: a vertex. • $$\H_a\$$: the foot of the altitude on side $$\a\$$; that is, the opposite side of the vertex $$\A\$$. • $$\T_b\$$: the foot of the bisector of angle $$\B\$$. Given these three points, recover the other vertices $$\B\$$ and $$\C\$$. ## Scoring & Winning criterion Every usage of the six basic constructions (shown above) counts. For the line intersections, creating each point adds 1 score, e.g. if you need both intersections of two circles, you get 2 score from the step. The solution with the lowest score wins. ### Scoring example Task: Construct the midpoint of two points $$\A\$$ and $$\B\$$. Solution: • Draw circle $$\C_1\$$ with center $$\A\$$ going through $$\B\$$. (+1) • Draw circle $$\C_2\$$ with center $$\B\$$ going through $$\A\$$. (+1) • Draw two intersections $$\X, Y\$$ of two circles $$\C_1\$$ and $$\C_2\$$. (+2) • Draw line $$\f\$$ going through the two intersections. (+1) • Draw line $$\g\$$ going through the two given points. (+1) • Draw the intersection $$\M\$$ of $$\f\$$ and $$\g\$$. (+1) The score of this construction is 7. ## Tools GeoGebra is a free online geometry tool. In addition to basic and advanced constructions, it has construction protocol feature which clearly shows the steps used to create the final image. For the above example task, the construction protocol looks like this: Out of 9 steps in total, the points $$\A\$$ and $$\B\$$ are given, so we can confirm that seven steps are taken for this particular construction. It also supports scripting (in GGBScript and JS) for those who want to view this challenge as or . Among many geometry commands, the Prove and ProveDetails commands may help you identify if a particular construction is indeed correct. ## Notes I'm using a relatively easy problem here, in order to see how this new challenge type is received. If it goes well, I'll propose some harder and open-ended problems later. ## Meta • Is this actually on-topic on PPCG? I'm asking this since this is the first challenge of its kind. I'll assume on-topic unless someone says otherwise on this meta question. • Maybe we need to tweak the difficulty of the challenge at hand. Is it too easy or too hard? Any other suggestions? I picked Wernick's list because it's not something you may see on Euclidea or similar, and the optimal (or elegant) solutions for many of the problems are not yet known. I'll go for the task this time, and try to ramp up in subsequent challenges. • I think it would be a stretch to consider this on-topic: proofs in logic can be argued to be as good as programs by reference to the Curry-Howard correspondence, but I don't really see extending that to proofs in general. It might be more interesting to instead ask for a program which generates proofs and score by the length of the generated proofs (although since the linked paper talks about a 6000-line program to search for them, that may be outside the scope of a reasonable PPCG challenge). – Peter Taylor Jul 23 '18 at 11:35 • On the difficulty of the given theorem: without much effort (5 minutes maximum) I have a solution scoring 16. It's certainly much easier than the existing proof-golf questions to get an answer, although I can believe that there may still be room to golf my solution. – Peter Taylor Jul 23 '18 at 11:38 • (In fact I've spotted one unnecessary intersection, so 15). – Peter Taylor Jul 23 '18 at 11:49 • Do you think this would be better here or on Puzzling? – user202729 Sep 30 '18 at 12:02 # The max() is not enough The max() is not enough • This could do with a better title, any suggestions? – ElectricWarr Oct 2 '18 at 22:14 • "Max is only half the story" – Quintec Oct 3 '18 at 2:06 • What if the largest integer in the list is not unique, do we output the second largest? I.e., with the list [1,8,4,8] do we output nothing because the 8 is duplicated, or do we output 4 instead being the largest unique integer? EDIT: Scratch the italic part before. Also, I assume we can take the input in any reasonable format? As an integer list, integer-array, integer-stream, comma-separated string, newline- or space-delimited STDIN, etc? Or is it mandatory to input it in a comma-separated string format? – Kevin Cruijssen Oct 3 '18 at 8:24 • Ignore the first question. Just noticed it's either nothing if all values in the list are unique, or the max otherwise (even if the largest is not unique). In that case: Can the list contain negative integers or zero? And are we allowed to output another falsey value instead of an empty output? – Kevin Cruijssen Oct 3 '18 at 8:25 • Can we have more test cases with all elements equal – Jo King Oct 3 '18 at 10:05 • I have a 5-byter ready, it's a great challenge if it isn't a duplicate! – maxb Oct 3 '18 at 12:40 • @Quintec Great suggestion to focus on "max" - definitely inspired the new title! – ElectricWarr Oct 4 '18 at 13:13 • @KevinCruijssen / Anyone: I think failing to follow the rules to the letter should be permissible BUT carry some level of bytes as a penalty. I'm not sure what the usual is here - how about 15 bytes each for either using some other input format and for outputting garbage instead of no output? – ElectricWarr Oct 4 '18 at 13:13 • @JoKing Of course, although I'm curious to know - is this somehow non-trivial to infer from the existing cases? What's the catch? :P – ElectricWarr Oct 4 '18 at 13:13 • @maxb This will like be up "for real" sometime tomorrow UK time. Good luck! – ElectricWarr Oct 4 '18 at 13:13 • Nah, but it would help people catch if their solutions are invalid. Also, I would discourage byte bonuses/penalties, and just let solutions take input how they like rather than overriding the site defaults – Jo King Oct 4 '18 at 13:28 • @ElectricWarr The default is usually to have a flexible input and output formats. But if you insist on having a string comma-separated input, then I will use a split by comma instead to make it into a list in my program itself instead of taking the 15 bytes penalty, considering my full program with list input is just 5 bytes, and changing the comma-separated string to a list is +4 bytes (way below 15 ;p). I would advice to don't use penalties or bonusses at all for challenges btw (and use flexible I/O, but the I/O choice is still up to you of course if you insist on comma-separated strings). – Kevin Cruijssen Oct 4 '18 at 13:31 • Btw, about "Assume input integers may be more than one digit but no larger than 4 bytes", your last test case has 6-byte numbers? – Kevin Cruijssen Oct 4 '18 at 13:36 • @KevinCruijssen I figure I'll try strict requirements this time around and if it's a problem I'll avoid them in future. On 6-byte numbers - ha! - good point, I'll reword that. Of course I should have foreseen that here of all places "bytes" is a measure of length first and as a quantity of information second! – ElectricWarr Oct 4 '18 at 13:46 • Polyglot, 30 bytes Takes +15 for not taking any input and +15 for not outputting anything – Jo King Oct 5 '18 at 1:54 # Formulize the sum: Faulhaber's formula Sums of the form Σkⁿ over k in 1..x can be turned into a polynomial of x whenever n is a natural number. ### Examples Σ1 = x Σk = (1/2)x²+(1/2)x Σk²= (1/3)x³+(1/2)x²+(1/6)x  ### Criteria You will take n as a non-negative integer input and output the coefficients in reduced fraction form of the resulting polynomial from leading coefficient down to the last non-zero coefficient. This is code-golf, shortest code wins. ### Test cases 0 #=> 1 1 #=> 1/2 1/2 2 #=> 1/3 1/2 1/6 3 #=> 1/4 1/2 1/4 0 4 #=> 1/5 1/2 1/3 0 -1/30 5 #=> 1/6 1/2 5/12 0 -1/12  (extra spacing here is just for clarity and is not necessary.) • 0 is positive? non-negative is better. – user202729 Nov 23 '17 at 13:40 • Fixed @user202729 – Simply Beautiful Art Nov 23 '17 at 13:41 • Is outputting floating point coefficient allowed? Is errors from floating point imprecision allowed? – user202729 Nov 23 '17 at 13:43 • @user202729 No, because you get some fractions like 5/12 or 1/3 with non-terminating decimal expansions. – Simply Beautiful Art Nov 23 '17 at 13:45 • What about the latter question? / Is errors from integer overflow (for large arguments) allowed? – user202729 Nov 23 '17 at 13:47 • @user202729 Yes, though you program should be able to handle up to, say, n = 20. – Simply Beautiful Art Nov 23 '17 at 13:48 • I think the answer for 3 should be 1/4 1/2 1/4. – alephalpha Nov 20 '18 at 17:03 • @alephalpha thanks – Simply Beautiful Art Nov 21 '18 at 18:31 • Don't we already have a Bernoulli numbers challenge? – lirtosiast Nov 26 '18 at 19:45 # The Hungry Moose Moose face harsh conditions during the winter. According to one source: Their winter foods are lower quality than what they eat in summer and provides less energy, consequently, they need to eat more of it. During harsh winters, having both extreme cold temperatures and deep snow, moose expend more energy than they take in and many can starve. ## Challenge At noon on day 1, a hungry moose starts at a food source (the top left corner). Each morning, the moose may either walk to any 8-adjacent square or stay in place. Each evening, the moose clears the food and snow from its location (adding its net nutritional value to its calorie store and setting that value in the array to 0), and before the end of the day loses 1 calorie to the extreme cold. The moose dies when its calorie store falls to 0 or below at the end of a day. In particular, if the value at the upper-left corner is 1, 0, or negative, the moose dies on day 1. ### Input A 2D array of integers. Negative numbers represent calorie-negative deep snow. ### Output The maximum number of days the moose can survive (counting day 1 as a full day). ### Test cases (add) 6 0 -2 3 0 0 -5 -5 0 0 -1 3 8 42 -100 1 -100 -100 2 3 4 5 42 5 -3 1 1 -9 9 12  • What happens if all the array values are all negative? Does the moose survive a single day or none at all? – Belhenix Nov 22 '18 at 20:21 • A worked example would be useful. You also need to clarify if we can wrap around the array. – Shaggy Nov 25 '18 at 14:28 # Extremely small data compressor In 2014 Jarek Duda at Purdue University wrote a paper containing several ideas for encoding computer data, entitled “Asymmetric numeral systems: entropy coding combining speed of Huffman coding with compression rate of arithmetic coding". The paper is available at Cornell University Library’s ArXiv project: https://arxiv.org/abs/1311.2540 One of the many fascinating things about this paper is that it begins by describing an extremely simple data compression algorithm, using the concept of the "Uniform asymmetric binary systems (uABS)". In fact, it is so simple, that you can implement it in only a few lines of code! Basically it attempts to interpret a sequence of input bits as a single integer - but by interpreting that integer using an alternative to our place-value binary number system, one can "shrink" the size of the input data. In other words, more 'likely' sequences of data will tend to map to 'smaller' integers. # Challenge You will implement the simple uABS compression algorithm, so that given a sequence of 0s and 1s, your program will compress them into a (usually) smaller sequence of 0s and 1s. ## Pseudocode The algorithm in psuedocode is as follows:  Begin with an integer X, and set it to 1 The input data is a sequence of symbols, each 0 or 1, called Input Find the probability P that any given symbol in Input is 1 For each symbol S in Input, set X to the output of the function Encode( X, S, P ) Output the final integer X as a sequence of symbols, 0s and 1s End  The Encode function itself can be described as follows: $$C(x,s,p)= \left\{ \begin{array}{11} \big\lceil\frac{x+1}{1-p}\big\rceil-1 & \mbox{if } s = 0 \\ \big\lfloor\frac{x}{p}\big\rfloor & \mbox{if } s = 1 \end{array} \right.$$ Where $$\begin{array}{11} C \text{ is the encoding function} \\ s \text{ is a symbol, either 0 or 1} \\ x \text{ is an integer} \\ p \text{ is the probability that any symbol in the Input data is 1 } \\ \text{ (the number of 1s divided by the total number of symbols)} \\ \lceil \rceil \text{ is the mathematical ceiling function } \\ \lfloor \rfloor \text{ is the mathematical floor function } \end{array}$$ ## Input and output format, notes, goofs and gaffes • The input is a sequence of symbols, each symbol being 0 or 1, in any method that is available in your chosen language. Examples include a sequence of ascii characters '0' '1', an array of integers, etc. • The output will be a sequence of symbols in the same format as the input sequence. The output sequence represents the compressed version of the input data. • Empty input data has undefined behavior. • Input data containing only 0s has undefined behavior. • When testing, note that some times input data may not be shrunk, and sometimes will grow. This typically happens when the number of 1s and 0s is relatively even. Data with an unbalanced number of 0s and 1s results in better compression. • You may assume that the number of symbols in the output is less than or equal to the number of bits in your language's largest integer type. The test cases outside this range can be ignored for your language. • Note that if you are trying to test this by 'decoding' or 'decompressing' the compressed data, and compare it to the original, one would have to store additional information, such as the length of input and probability P, but for simplicity this has been left out of the challenge. # Example Input and Output Short examples: Input Output 10 101 10010100000 1011101001 1111 1 11111111111 1 10000000 11011 10011111010101 10110000100101  Longer examples: Input 11111110110111110111111111011111 Output 11111000011110110 Input 000000000001000000010000000000001100000000001 Output 1110000101100111000011111 Input 000000000001000000010000000000001100000000001000000000000000000000000000000000000000000000000000000000000000001 Output 1010100110111110010111011110110101010  # Scoring • Have fun! • The program with the fewest number of characters wins! • 1. IMO the pseudocode could be made clearer by firstly explaining what "machine integer" means (does it mean "unbounded integer" aka "big integer"?) and secondly golfing it a bit: using a "foreach" loop notation for S and eliminating the variable X'. 2. I think it would be helpful to be explicit about how p should be derived from the input. I presume that it means looping over the input twice, once to count and once to compress. 3. IMO restricting the input format to strings of ASCII 0 and 1 detracts from the core challenge. Why not allow arrays/lists of integers? – Peter Taylor Jul 7 '18 at 12:13 • Thanks, i have revised. – don bright Jul 7 '18 at 14:08 • I really like this one. Something quasi-practical, and yet simple and small enough to be fun. Just to be clear, the output is the binary representation fo the integer X, without any leading zeros, correct? – sundar - Reinstate Monica Jul 8 '18 at 19:02 • Also, you mention "input size of at least 128 symbols", but it might be more important to specify output size limit, since many languages have hard bounds on maximum integer size. Since output size varies for the same input length, it might have to be something like "you may assume that the number of symbols in the output is less than or equal to the number of bits in your language's largest integer type". (The last test case would then be optional in languages that can handle only up to 32 bit integers). – sundar - Reinstate Monica Jul 8 '18 at 19:12 • yes the output is the binary representation of the final integer X, i believe the leading zeros is correct. do you think 32 bit is the good limit or 64, since modern machines tend to be 64 bit? thanks – don bright Jul 8 '18 at 20:05 • 32 is probably a reasonable limit, one that most languages can handle without need for external libraries. – sundar - Reinstate Monica Jul 14 '18 at 14:22 • @sunar thanks, i have updated. – don bright Dec 29 '18 at 14:21 • I assume the intent is for P to be calculated as # of '1' in the input / # of symbols in the input? That seems like it would match the definition given, but it would be helpful if it's described explicitly. – Kamil Drakari Jan 3 at 22:24 • Done, thanks.... – don bright Jan 3 at 23:32 ## Inscriptio Labyrinthica In the burial place of King Silo of Asturias there is an inscription that reads SILO PRINCEPS FECIT (King Silo made this). The first letter is found in the very middle, and from there one reads by going in any non-diagonal direction radiating outward. The final letter is found on all four corners. In this challenge, you'll generalize the process to make them. ## Input A string (or equivalent), and an integer. You may make the following assumptions about the input: • The string will have an odd length. • The integer will be an odd number between 1 and one less than twice the length of the string. ## Output An inscriptio labyrinthica for the string, using the integer for the height (see models). Output should be each letter with no spaces, line break as default to your system/language. ## Test cases Note that an input of 1 or (length * 2 - 1) will result in a horizontal or vertical palindrome.  Input: FOO, 3 Input: BAR, 1 Input: BAR, 3 Input: BAR, 5 Output: OOO Output: RABAR Output: RAR Output: R OFO ABA A OOO RAR B A R Input: ABCDE, 5 Input: ABCDE, 3 Input: *<>v^, 3 Output: EDCDE Output: EDCBCDE ^v>v^ DCBCD DCBABCD v><>v CBABC EDCBCDE ><*<> DCBCD v><>v EDCDE ^v>v^  ## Scoring This is so shortest answer in bytes wins. Standard loopholes forbidden. (I feel like I've seen one similar, but searching around I couldn't find it, and I happened to be reading about this king when I got the idea). ## Questions In my original proposal, I had listed as a bonus to draw reading lines, but feedback was bonuses in code golf are discouraged. I still like that idea and am thinking about integrating it as a a main part of the challenge, but don't know if that would over complicate it or actually make it more interesting. The output for REI, 3 in such a case would be I←E→I ↑ ↑ ↑ E←R→E ↓ ↓ ↓ I←E→I  The idea is that it would prevent simple flipping of data after calculating a quarter or half of the but still perhaps allow for some creative ways (I can think of some creative ways to do it shortly in some languages, but maybe it'll be overly complicated for others). • @trichoplax I've updated the challenge based on your feedback, let me know what you think. – user0721090601 Jun 30 at 17:20 • Looks good to me. +1 – trichoplax Jun 30 at 18:24 • you should now edit this to a link to the post and delete it. Thanks! – Giuseppe Jul 24 at 19:11 # Golf the truth and null values In many programming languages there is a null and/or other special values. Sometimes they don't follow the normal rules of boolean operations. They may not even agree with the values of the same name in other languages. Here are some different kinds of the "extended" boolean values, either borrowed from some languages or invented myself: • False. • True. • Absent. All operations between absent and another operand return the other operand. • Whatever. All operations between whatever and another operand returns whatever (itself). • Partial. If the result can be decided using the other operand, return that. Otherwise return partial (itself). • Error. An error as the first operand works like whatever, and an error as the second operand works like partial, except that "itself" means error. It has higher precedence than whatever and partial. Your task is to define all these values in your language, and the 2 operations and or. To be clear, the 2 operations should work exactly as in the following tables. The left column represents the first operand, and the top row the second operand. and F T A W P E or F T A W P E F F F F W F F F F T F W P E T F T T W P E T T T T W T T A F T A W P E A F T A W P E W W W W W W W W W W W W W W P F P P W P E P P T P W P E E E E E E E E E E E E E E E  ## Rules You could use anything distinct and consistent to represent these values. You don't have to use a truthy value to represent true, or a falsy value to represent false. You are allowed and encouraged to use values that contain useful code, i.e. this loophole is not forbidden. You are allowed to use actual errors or exceptions to represent some of the values. In this case the definition of that value should throw the same error, instead of represent the caught error. But the caught errors or the output messages should be distinct and consistent. Alternatively, you may choose to include STDERR in the output of your code, and use the printed message string as a normal value. You may choose to pass functions generating and returning the values but doing nothing else to your code as input, in place of the values themselves, without counting the extra code. You may use different ways of input/output for different values, as long as it is consistent for each kind of value, and it is possible to tell apart the first and the second operand. You are allowed to use builtin functions and operators without boilerplate, in any argument order, even if you cannot save them in something callable in your language. There could be some common code shared by all the 8 definitions and appear only once as header/footer. Other than that, the 8 definitions of operations and values must work independently from each other. The only way you can call something defined in the values in the operations is through a valid input method (e.g. you cannot set a variable in a value and read it in an operation). Your score is the length of common code * 12 + the total length of the 2 operations * 6 + the total length of the values. Smallest score wins. The length of a value is either the length of the code generating it, or the length of itself unquoted if all the values are strings and you choose this way. ## Abandoned rules You are allowed to use operators, or chains of operators and values to represent the 2 operations, even if you cannot save them in something callable in your language. You may require the operands to appear at specific positions, but each operand must appear exactly once and be grouped together. You may choose whether to save operands in variables previously, and don't count the assignment if it doesn't add new information in the assignment (e.g. by changing its type). This makes it possible to use the built-in operators with short-circuit evaluation in languages that don't allow redefining them and preserve this characteristic, and may also make it shorter in some other languages. Previous scoring: total length of the 2 operations * 50 + the total length of the values. ## Possible follow-up Original title: All the weirdness about the nulls Extended tables including Valid in a previous version, Reverse aka Opposite by Zgarb, and Possible. and T F N O W E V R P or T F N O W E V R P T T F T O W E ? F T T T T T T W T T T T F F F F F W F F F F F T F F O W E ? T F N T F N O W E ? ? ? N T F N O W E ? ? ? O O F O O W E ? O O O T O O O W E ? O T W W W W W W W ? W W W W W W W W W ? W W E E E E E E E ? E E E E E E E E E ? E E V T F ? O F F ? ? ? V T T ? T F F ? T ? R F F ? O W ? ? ? ? R T T ? O W ? ? ? ? P T F ? O W ? ? ? ? P T F ? T W ? ? ? ?  Other potential additions: • Default, that is opposite to Opposite. • Merge Possible with Valid. ## Sandbox questions 1. Will this be too easy in some languages that already have all of them? In languages that has True defined to be -1 and unifies bitwise and logical operations, most integers would works as Partial. GCD/LCM in APL is similar to this. SQL null is Whatever Partial. Most languages that has shortcut evaluation has errors as Error. Not sure about Absent, though. (Maybe the easiest way to find out is to post this question. It doesn't make the answer bad. But it's just some consideration in the sandbox for me to decide whether I'll post a stronger version.) 2. Allowing "operators and chains of operators" seems to open a can of worms. Should I just remove this rule? • How about Opposite that behaves like the negation of the other operand? – Zgarb Dec 11 '16 at 19:10 • @Zgarb Too similar to Other. For the "2 more to be added", I intended to make it possible to write expressions to 1) decide whether a variable is a specific value, and 2) return a specific value if a variable is true, or false otherwise. This may make the list more useful later. – jimmy23013 Dec 11 '16 at 19:42 • @Zgarb I gave up and even removed one, to make hardcoding the tables less likely to be the optimal way. – jimmy23013 Dec 13 '16 at 17:56 • if(whatever){/*???*/} – Pavel Dec 13 '16 at 20:23 • @Zgarb I forgot this post for some reasons. Now I found your idea quite interesting. But I'll post the first version without it, and may add a stronger version if it worked well or is too easy, and may name it Degenerate to make most of the other results from operations make sense. – jimmy23013 Apr 30 at 8:40 # Knight's tour A knight's tour is a sequence of moves of a knight on a chessboard such that the knight visits every square only once. For those who are not aware of how knights in chess work, knights are capable of moving in an L shape: Tours generally apply to a regular chessboard of size $$\8\$$ however, it can be calculated for other sizes. For example, for a chessboard of size $$\5\$$, a possible knight's tour is: Each grid size has quite a few combinations, for example, when $$\n = 5\$$, there are $$\1728\$$ possible tours and for a regular chessboard (where $$\n = 8\$$), there are $$\19591828170979904\$$. This is OEIS A165134. ## Challenge Write a program/function that takes a grid size $$\n\$$ and outputs a possible valid board of integers. ### Specifications • Standard I/O rules apply. • Standard loopholes are forbidden. • $$\n > 4\$$ • This challenge is not about finding the shortest approach in all languages, rather, it is about finding the shortest approach in each language. • Built-in functions that compute this sequence are allowed but including a solution that doesn't rely on a built-in is encouraged. • Explanations, even for "practical" languages, are encouraged. ### Test cases Yet to come. • "Your code will be scored in bytes, usually in the encoding UTF-8, unless specified otherwise.": So a Jelly answer will need to specify "Jelly (Jelly codepage)" or else it needs to count bytes of a unicode encoded source? Why not leave it out and let the tag code-golf handle the rules. And instead of generating test-cases, you could just add a program that validates the result as there are a lot of possible answers . – ბიმო Sep 22 '18 at 14:19 • @ბიმო Heh, I did this back with all my challenges when I was obsessed with creating "the perfect challenge template." I'll remove it. As for the test cases/validation program, I'll probably do both. – totallyhuman Jul 12 at 1:55 • @lirtosiast Oops, turns out I had mistaken the meaning of the Wikipedia section I just linked. I'll specify that a submission is not required to work on any \n < 4\. – totallyhuman Jul 12 at 2:00 • Another Mathematica built-in is coming~ – tsh Jul 12 at 7:27 • Can output be a list of coordinates? – tsh Jul 12 at 7:29 • Having both test cases and a validator sounds good to me too – trichoplax Jul 14 at 7:59 # Babel on and on (working title...) ## Background Babel is a cornerstone of modern web development. It takes Javascript using new or proposed ECMAscript features and "transpiles" it into an older language version, so that browsers can run it without updates. In order to do this it inserts its own shim methods, and own custom transforms. ## The Challenge Your objective is to write the Javascript code which produces the largest babel output in characters. Your code must be less than or equal to 128 bytes in length Babel has an online, interactive compiler which you can access HERE. It's highly recommended that you use this to form your answer. If you work locally, you are restricted to modifying only the settings that the babel website allows you to modify.. There is a guide on installing babel at the end of the question. ## Rules • For consistency, you may use a Babel version between 7, but not above 8.* (when it eventually comes). • You may change the interactive REPL's settings, source type, presets, options, and env-presets. You may change these settings locally if you are using a local installation of babel. • You may only provide one input file. • You may not exceed 128 bytes in your input file. • You may not add your own plugins. • You may not use the loophole listed below, or any of the standard loopholes. • You may not use error output as a result. babel must transpile the code successfully under one of the allowed configurations. • Neither your input or output need to run, or halt. The compilation just needs to output something. # Examples 41 in, 1075 out {t: [...(function*(){let [a,b]=[1,2]})]}  32 in, 1101 out export class b{d=function*(){}}  125 in, 7336 out const b = function*(){return function*(){return function*(){return function*(){return function*(){return function*(){}}}}}};  # Scoring You must provide both the code and the settings you are using. For users of the online REPL, a link with the settings set in the URL suffices. The answer with the largest output with an input less than or equal to 128 bytes wins. Unlike many challenges of this nature, settings do not cost any bytes of input. # Setting up a local environment (OPTIONAL) Most of the people doing this challenge will probably use babel's online transpiler to complete it. In the event that the website is taken down in the future or made inadequate for the challenge, it can be completed locally. Make a folder for the challenge, and in a shell in that folder, try something like the following: Install Babel (globally - you could do it locally) sudo npm install -g @babel/core @babel/cli Set your .babelrc with a preset (in this case env) echo '{"presets": ["@babel/preset-env"]}' > .babelrc Install babel's dependencies npm install --save-dev @babel/preset-env @babel/core Then, given an input file test.js, you can figure out your output score with babel test.js | wc -c # Happy Hunting! # Questions This is my first time ever posting one of these. Does everything look on the up-and-up? Also, should this incorporate "the less characters of input, the better?". I kept trying to think of ways to reward a large output for a small input, but every way I considered changed the tone of the challenge significantly. Also also, I know that codegolf users don't like being constrained to one language. Is this bound to be an exception or will that stop the question in its tracks? Proposed Tags: [BUSY BEAVER], [Javascript], [CODE CHALLENGE] • Hi and thanks for using the sandbox! I'll start right off by saying I don't know enough about babel to particularly talk about if this will be interesting. I think this kind of challenge is fine, just like regex-golf. This should probably be tagged code-challenge and shouldn't be tagged compiler. I am concerned that you tie everything to an external site. While I doubt the site will go down, what happens when they update babel? Will it break the challenge? Since this is a bit abnormal, you may want to ask on meta (specifically about the online scoring) or in chat for more feedback. – FryAmTheEggman Jul 1 at 21:56 • @FryAmTheEggman thanks for the tags and pointing me to meta for this, I think I'll wind up clarifying things over there. And also, about the foreign site - it's not required, but makes it far, far easier. That's why I edited in the clause about being able to do it locally. If the site is used, the settings are query parameters in the URL (but could be interpreted even if it went down). And contestants can do it locally, provided they post the settings they use, and use the same version. So I'm not too worried about tying it to a site, since it's just for convenience. – Nathaniel Pisarski Jul 2 at 12:52 • We discourage language specific challenges when there is no reason for it, but here it is clearly part of the challenge so I see no problem at all. – trichoplax Jul 16 at 20:42 • Having a fixed number of input bytes to work with can be awkward in language agnostic challenges as it's difficult to choose a suitable number that doesn't make it too difficult / too easy for some languages. Since everyone is using the same language here a fixed 128 bytes seems reasonable. Your examples already show it doesn't need to be higher. You could consider lower, depending on how you want the challenge to go. With 128 bytes there's a good chance some outputs will be too large to fit in the 65536 character answer length limit, but I don't see that as a problem either. Looks good to me – trichoplax Jul 16 at 20:47 ## Castilian Numerals A little known (but actually real) number system are the Castilian numerals. They were an odd mix of a digital and positional counting system used in Spain in the late middle ages. There are certain qualities about them, however, that make them not entirely straight forward to generate when you have lots of them in a group, in particular the fact they would be aligned by thousands places. Your challenge will be to print a vertical list of numbers, correctly spaced. ## Description of the Numerals A Castilian numeral is, in effect, a Roman numeral, but only uses 1-999, uses additives for 4 (IIIJ), 9 (VIIIJ), and 900 (DCCCC), and subtractives for 90 (XC) and 400 (CD). Both methods were commonly used for 40 (XL, XXXX). Additionally, final Is were written as Js, such that the sequence 1-6 goes J, IJ, IIJ, IIIJ, V, VJ. (This means standard Roman numeral generators will likely not be much help.) They were generally written lowercase, but for this challenge we'll use all uppercase. For values under between 1-999, the fact that the letters indicated numerals was made clear by the presence of a symbol that looks like a U. Generally the numerals themselves were right aligned: 1 U J 2 U IJ 999 U DCCCXCVIIIJ  For values between 1000-999999, everything we would place to the left of the comma would be rendered as if it were its own independent 3-digit number and romanized, and the reminder placed to the right, such that  1,000 J U 1,001 J U J 21,030 XXJ U XXX 500,444 D U CDXXXXIIIJ  For values 1,000,000-999,999,999, an additional separator was used, Qto, but for our purposes, we'll just use Q. It would only be used if the number was over 1,000,000, unlike the U that always separated it.  1,000,000 J Q U 1,000,001 J Q U J 1,001,000 J Q J U 1,001,001 J Q J U J 123,456,789 CXXIIJ Q CDLVJ U DCCLXXXVIIIJ  As should be noticed, within each grouping of three (arabic) digits, everything is right aligned, with the thousands/million separators all in alignment. Because 0 didn't exist, it would just be left blank. ## Input A sequence of integers in whatever format you feel gives you the best advantage (a list, an array, a series, etc). You may assume that the integers are between 1 and 999,999,999. ## Output A printed list of Castilian numerals, properly aligned on different lines. Note the restrictions on 4/9: mandatory additives are 4,9,900; mandatory subtractives are 90 and 400; 40 is valid either way. The numerals for 1-999 should be right aligned, with a single space on either side of Q or U (there may be padding spaces, but the single longest numeral in each grouping will have the single space). Newlines may be whatever is native to your system/language. ## Rules This is code golf. Fewest bytes wins. Standard loopholes forbidden. ## Test cases Comments/observations are given after # and not part of the output. Given: 1,2,3 U J U IJ U IIJ # one space between U and I Given: 1,1000,10,100 U J J U # trailing space not required U X U C Given: 123,4,5678,111111111,90,12345,6789012 U CXXIIJ U IV V U DCLXXVIIJ # single space between U and the longest numeral CXJ Q CXJ U CXJ # Q only appears if >= 10^7 U XC XIJ U CCCXXXXV # also valid CCCXLV VJ Q DCCLXXXIX U XIJ # single space between Q and the longest numeral  # Character Frequency in a String Posted here. • i dislike the special case of space – Jo King Jul 21 at 1:25 • @JoKing If there was no special case for space, a string like 1 a would look something like 1 1; 1;a 1. Also, it's for the challenge. – bigyihsuan Jul 21 at 3:19 • I'm with @JoKing on this; nothing is added to the challenge by special-casing spaces. – Shaggy Jul 21 at 21:08 • I'd like to further say that restricting the output this much doesn't seem to add much to this challenge. Why isn't, for example, a list of pairs acceptable? I can't find any justification for your output rules. That's not to say you can't do it, but I have a hard time imagining it will be popular. – FryAmTheEggman Jul 22 at 18:58 • – AdmBorkBork Jul 23 at 20:15 • @AdmBorkBork, having since given it a try in JS, I'm pretty sure there's a closer (potential) dupe target than that. – Shaggy Jul 23 at 22:12 • Having posted this, you should delete the sandbox post. – Adám Jul 24 at 6:29 # Golf range minimum queries of a list Looks like this post hasn't gotten any problems called out, but also not that much support. If you could leave even a brief comment if you don't like it, that would be much appreciated. (Inspired by the first problem solved in Stanford’s advanced data structures course.) Despite the academicese-heavy name, the problem we're going to solve is almost unbearably simple. We have a list of numbers. [31, 41, 59, 26, 53, 58, 97]  We're going to cut some contiguous snippet out of that list of numbers. [31, 41, 59, 26, 53, 58, 97] |41, 59, 26, 53|  And then we're going to find the minimum of that snippet. In this case, that's quite obviously 26. That's all. And the obvious solution is pretty fast, too, with O(n) time and O(1) space in the size of the list: minval = arbitrarily large value for (i=first snippet index, i<last snippet index, i++) if (list[i]<minval) minval = list[i]  ### So what's with the fastest-algorithm? Where it gets interesting is when you try to see how efficient you can make it when you have a fixed list but a large number of range minimum queries -- snippets to find the minimum of. This version of the problem is useful, for example, if you have a huge time series you want to load only once, but you want to find the minimum of many different subintervals of that time series. In such a scenario, it would actually be faster in practice to literally precompute all n**2/2 queries, store it in a table, and then just retrieve data from that table for an O(1) time and O(n**2) space solution. ^dynamic programming solution taken from the Stanford slides And then if you're clever enough, you realize that you only have to store each query with size that's a power of two -- you can just combine those power-of-two minima to sum to an arbitrarily sized query, and achieve the same results with constant time and linearithmic rather than quadratic space. Interestingly, if you keep optimizing, you can get to an O(1) time and O(n) space solution using a sort of augmented list known as a Fischer-Heun structure. I'd love to go into the details of the structure here, but explaining how it weaves into Cartesian tree building on fixed-size snippets would make this question about 50 pages long. It's explained in the Wikipedia page linked in the title (which I've copied here), however, along with several faster-than-linear intermediate structures. (If you can get past a research paywall, here's the original Fischer & Heun 2011 paper. And if you’d prefer the much more verbose but much more hand-holdy Stanford lecture style, here are the follow-up slides that goes into this solution, including lots of intermediates.) ## The challenge You can either write a full program or a function that calculates the result of a series of range minimum queries given a fixed list. Scoring is set up such that in general, the shortest and most-efficient-over-lots-of-queries code wins. Input: A list of integers xs, followed by a series of i, j pairs denoting the start and end of the snippet, inclusive (so the 26 example above uses indices i=1 and j=4). The list of integers is guaranteed to have at least one integer, and 0 <= i <= j < len(xs). This can be taken in any format that works best for your language — for example, one list for xs and one list of tuples for the i, j pairs; or maybe all the different pairs as a variable number of arguments. For a full program that takes in input from stdin, I’ll fix a format for the input: xs[0] xs[1] xs[2] xs[3] ... i1 j1 i2 j2 i3 j3 ...  Output: An ordered collection of the range minima for each i, j query, in the same order that they were given. In case an unordered map (such as a Python dictionary) from each i, j query to its range minimum works better for your language, that will also be allowed as an output; as long as it's obvious which minimum is related to which query. Once again, for a full program that prints to stdout or a file, I’ll fix the format to have each range minimum on each newline (trailing newlines permitted). ## Scoring: Lower score is better; score is determined by at(b)^2+as(b)  Where b is the byte count of your code, at is the asymptotic runtime Ө(n) of the algorithm in the size of xs interpreted as a function of n, and as is the asymptotic space usage Ө(n) in the size of xs interpreted as a function of n.( All constant coefficients in such Ө(n) expressions must be 1, and only the fastest growing term may be kept in expressions, as is standard.) Therefore, the above pseudocode solution, which uses Ө(n) time and Ө(1) space, and is 126 characters, would have a score of (b => b**2 + 1)(126)=15876+1=15877. (Of course, the pseudocode isn't really valid since it's missing a construct to deal with multiple queries, and also because it's uncompilable pseudocode...) ## Test cases: Input: 31 41 59 26 53 58 97 1 4 0 2 5 6  Output: 26 31 58  Input: 1 0 0 0 0  Output: 1 1  Input: -4 28 31 -54 0 0 0 1 0 2 0 3 1 1 1 2 1 3 2 2 2 3 3 3  Output: -4 -4 -4 -4 28 28 -54 31 -54 -54  # Sandbox Questions: • Would the asymptotic runtime count as a non-observable requirement? • is this too long and/or abstruse lol • I’m not sure how to word the scoring section to narrow down the most obvious, basic O(n) expression — an algorithm that’s Ө(n) is also Ө(n/16384-50000) by definition. Is what I have clear enough? Have I left any loopholes? • I kind of wanted to encourage people to try to implement Fischer-Heun or one of the more time-efficient intermediates in the slides, without restricting them to one particular algorithm (e.g. challenge: you have to make a Fischer-Heun structure). Does the scoring system make sense for this? Is it fair to have, for example, a Jelly answer using the naive algorithm in 3 bytes (score 10) compete with a Jelly answer using the Fischer-Heun structure in 30 bytes (score 31); but a naive Python answer with score 3000+ compete against with a Python Fischer-Heun with score 300? • [tag:tag-name] – Adám Jul 30 at 19:06 # Game of Game of Life Conway's Game of Life is a 0-player game. But that's okay! We can make it a multi-player game. This game is played on the smallest square grid that will accommodate a 6x6 square for each player (12x12 for 2-4 players, 18x18 for 5-9 players, etc). This grid is actually a torus, so it wraps in both directions. The rules of Life are: • If a cell has exactly 3 neighbours, it comes to life (or remains alive) in the next generation. • If a cell has exactly 2 neighbours, it does not change in the next generation. • If it does not have 2 or 3 neighbours, it dies in the next generation. A cell's neighbours are those cells adjacent to it orthogonally or diagonally; each cell has 8 neighbours. In this game, there are only a few differences from the standard Game of Life: • Each player has a different colour of life, with dead cells being white and neutral living cells being black. • When a cell becomes alive, it takes on the colour of its most common neighbour, or black (no player) if there are three different colours. Cells do not change colour as long as they are alive. • Each generation, each bot can cause one nearby cell to come alive in their colour or one of their own cells to die. This happens before a generation is processed; a cell that is killed may come back to life and a cell brought to life may die in the subsequent generation. # Winning the game The game lasts 1000 generations, or until there is only one colour of living cells remaining. If all coloured cells die on the same generation, the game is a draw, and no bot receives points. Each bot scores points equal to the percentage of living coloured cells it has at that time (out of the total number of coloured cells). 1000 games will be run, and the winner is the bot with the highest average score. Ties are broken with a 1v1 cage match. # Starting conditions Each bot will start with the following layout of living cells: ...... ...... ..##.. ..##.. ...... ......  These will be randomly arranged into the square playing area. Each 6x6 area without a bot will have the same configuration, but with black living cells. # Bot parameters Your bot will be written in Javascript, and will not have an average call time of over 50ms (bots that do may be disqualified, but bots may use performance.now() to police their own time). It will accept as parameters: grid - The grid on which the game is played. This should not be modified. botId - The bot's ID, corresponding to the colour on the grid. lastMoves - An array of each bot's most recent move, as it's (usually) possible but computationally intensive to get this information otherwise.  Your bot will return an array with two elements, x and y. This is the cell that your bot wishes to play. It must be within 2 cells of one of your living cells. If the selected cell is alive and not one of your cells, it does nothing unless the bot whose colour it is removes it on the same generation, in which case it causes it to be your colour. If it is alive and one of your cells, that cell is killed before the next generation. If it is a dead cell, it comes alive before the next generation (it comes alive as your bot's colour unless some other bot also picks it, in which case it comes alive black). A play too far away from one of your cells is a pass. Alternately, [-1,-1] is an explicit pass. A play off of the board in any other way is illegal and grounds for disqualification. # Other Restrictions • You may make a maximum of 3 bots. • If your bots uses random numbers you can use Math.random. • Your bot may, if it wishes, store data on this. It will be cleared between games. • You may not make a bot which targets a single, prechosen bot. Your bot may target the tactics of a class of bots. • Cooperation is legal between bots, but communication is not - you can cooperate with a strategy, but not attempt to make a specific sequence of moves which identifies your bot. For example, identifying a bot based on specific starting sequence is not allowed, but knowing "target bot prefers moving up and left, all else equal" is okay. IDs are randomized and bots will not know in advance what other bots' IDs are. # Controller Not built yet. # Sandbox Questions • Is this clear? • Have I missed any common loopholes I should really close? • The initial set of squares should have a guaranteed distance from each other set of squares. grid needs better specification. What does "nearby square" mean? Other than that, solid spec. – Nathan Merrill Oct 31 '18 at 13:12 • 1) The wording is weird on the Game of Life rule explanation. Please take a look at the Wikipedia page and clarify them. Currently, I'm not sure if a cell can change color if it's surrounded by more opponents than allies. Also, it seems to be implied that a live cell surrounded by 3 neighbors dies (which I'm pretty sure wasn't your intention). 2) What happens when no colors remain on the board? 3) Nitpick: the "this" in "it has at this time" threw me off - "that" instead, perhaps? – Alion Oct 31 '18 at 13:18 • 4a) Since there's no explicit ban on cooperation, it's allowed by default. Was this your intention? 4b) Can bots communicate with each other? 5) Can bots store data across games? 6) Can we get a more easy-to-use system of storing data within one game? Scopes are useful for this: function externalFunc() { /* Storage */ return function gameLoopFunc(args) { /* Code */ }; } 7) next is not very robust. Some people (including myself) will remake the game simulation to gain access to more advanced functionality. 8) What happens if the returned value isn't within 2 cells of one of my own cells? – Alion Oct 31 '18 at 13:30 • 9a) Why is selecting a live cell that is not your own a legal move, despite not doing anything? 9b) Is it legal to pass a move always? If so, what should we return if we want to pass a turn? 9b2) If it's not legal to pass a turn... why? It sounds pretty useful and makes sense. Please consider it. – Alion Oct 31 '18 at 13:33 • @NathanMerrill Thanks, I've clarified that now. – Spitemaster Oct 31 '18 at 13:46 • @Alion I've fixed 1, 3. I've removed next - good point (7). I've changed access to localStorage to access to this, clears between games (5,6). I've changed the scoring to a percentage and clarified draws (2). I've clarified that passing values out of bounds is illegal (8) and what (9a) does. I've also made passing legal (9b/c). (4) I did intend for cooperation (but not communication) to be legal; I've clarified that. Thanks for all the help! – Spitemaster Oct 31 '18 at 14:02 • Splendid work. That being said, I'm not done yet. 10) Typos: id > it (line 2 of rule explanation), bot's > bots' (last restriction). 11) Can bots modify the grid passed to them (in the non-malicious sense)? 12) Black doesn't immediately strike me as a living cell. I'd recommend specifying that there exist neutral living cells (I only realized this during my 4th reading). 13) What format should submissions be? Template and example submissions both work. 14) Controller: If you haven't already, you should check out Dave's JS KotH framework. – Alion Oct 31 '18 at 15:21 • 15) You've opened Pandora's Box with cooperation restriction. I'll illustrate what I mean with several abstract examples. GrudgeBot and PassiveBot: GrudgeBot will not attack PassiveBot, because PassiveBot doesn't bother GrudgeBot. FriendlyBot: Attempts to make friends with bots that it comes into contact with by testing if they will attack it. 2 instances would quickly team up after meeting each other. AlgoBot: Runs simulations and tests how well other bots play according to its idea of "optimal". 2 instances quickly realize that the other is playing optimal or near-optimal moves and team up. – Alion Oct 31 '18 at 15:40 • 15 cont.) So, where do you draw the line? 16) performance.now() for timing purposes. Introduces unpredictability, but lets bots police their own time instead of their creators having to wildly guess the right values. Allowed or not? 17) cellular-automata, game, grid (maybe). – Alion Oct 31 '18 at 15:44 • Whew, what a rampage. Despite all of that, I'm impatiently looking forward to this hitting main. Expect to see me there immediately. Keep up the good work! – Alion Oct 31 '18 at 15:47 • Thank you very much! I've fixed (10)-(12). I'll add an example submission when I'm finished the controller - and I will definitely check out that framework! (15) - Good point, but I don't want to give an advantage to people who build multiple bots. I've added a clarification that a test for "too much cooperation" is preset move sequences and the like - identifying a bot by its strategy is okay. There's room for interpretation, but I trust that non-malicious entries will be reasonable. All of your examples I'm okay with. :) I will add some tags. – Spitemaster Oct 31 '18 at 15:58 ## Polyglot wrappers Many polyglots are a disastrous mess of unmaintainable code. Let's make this different. Challenge Make a polyglot "wrapper" such that code from two or more languages may be embedded in the file without modification. Example Consider the following polyglot wrapper for Bash and Python: '''true' B exit 0 #''' P  This wrapper can be used such that B can be replaced by an arbitrary bash script, and P can be replaced by an arbitrary python script. After the scripts have been injected into the wrapper, running the resulting polyglot via either interpreter (bash or python) will result in functionally identical behavior as the original input scripts. Rules 1. Your wrapper must support the injection of 2 or more languages 2. Your wrapper can use arbitrary markers for the string->script replacement 3. The markers must be at least 1 byte in size (no line number tricks) 4. Assume the replacement will be done by first replacing all markers with sufficiently long and random data, such that conflicts between the marker literals and contents of the input code cannot exist. However, your markers cannot conflict with the contents of the wrapper itself. 5. The behavior of the original input programs must not be altered by the wrapper. Ex: an input program that returns 0 must return 0 when run from your wrapper. An input program that crashes must still crash. 6. The winner is the polyglot wrapper that supports the most languages, with a tie breaker of smallest size (in bytes). 7. Allowances shall be made for a program that accesses itself on disk. Obviously no polyglot wrapper could correctly return identical output for a script that outputs its own file size. Question for the sandbox Is this sufficiently unique and understandable? Are there any loopholes I haven't covered? • What if, for example the bash script contains '''? Is that what rule 4 is talking about, since I don't really understand that rule. – Jo King Sep 2 at 5:51 • I'm indeed wondering the same as @JoKing. What if the content of the code we'd potentially insert into the wrapper contains something that could break the wrapper or other program itself? For example, let's say I submit 0W, where 0 is a wrapper for a 05AB1E program, and W for a Whitespace program. 05AB1E in general ignores all whitespaces between commands and Whitespace ignores all characters except for spaces/tabs/newlines. But what happens if the potential 05AB1E program contains a string with a space/tab/newline in it, which would interfere with the Whitespace program? – Kevin Cruijssen Sep 2 at 9:25 • Perhaps make it such that the inner programs are a turing complete subset of the parent language, such that the overall program will always run correctly. Answers would have to make a list of restrictions placed on the language subsets, as well as prove that they are still turing complete, and can't 'break out' of their wrappers, nor have effects on other sections of the program – Jo King Sep 2 at 12:08 • Would this work as a cops and robbers? Cops provide wrappers and robbers provide code that breaks the wrappers? – trichoplax Sep 3 at 11:49 • Good catch, everyone! I'll have to think about this some more. Cops and robbers sounds like a good way to make that problem into a feature, @trichoplax – BLuFeNiX Sep 3 at 14:16 • Your example can break in a different way too. An unterminated here-doc in bash will continue until the end of the script: B = cat << EOF – GammaFunction Sep 8 at 6:29 # Solve the Levenshtein distance traveling salesman problem fastest-code Note: don't miss the tag! The Levenshtein distance between two strings is the smallest number of single-character edits (insertions, deletions and substitutions) necessary to make them equal. You are given a set of lowercase alphabetic strings. The task is to find the shortest route that visits all of them at least once and ends where it started, where the distance between two strings is the Levenshtein distance between them. If there are multiple such routes with the same total distance, you can output any of them. TODO: test cases and many other things (once I get enough feedback to tell whether this is a good idea) • Nice one! I think you may clearly specify if the strings have to be visited following the order of the list or any order. – AZTECCO Nov 10 at 12:18 • @AZTECCO The challenge would be fairly pointless if the order was specified (since the challenge asks you for the order). – my pronoun is monicareinstate Nov 10 at 12:19 • Ok, so the task is to visit all of them and end at the starting point? That's what circular refers to? – AZTECCO Nov 10 at 14:05 • Yes. I think I'll clarify that. – my pronoun is monicareinstate Nov 10 at 14:07 • Per StackExchange policy, I recommend changing "salesman" to the inclusive "salesperson". – Greg Martin Nov 11 at 17:39 • @GregMartin I can see what your saying regarding gender neutrality, but I think that might get in the way of clarity since it's the canonical name of the problem and someone could semi-reasonably assume the problem is a different problem. Google autosuggests "Travelling Salesman Problem" when feeding it 'salesperson' and Wikipedia does a similar redirect. Though perhaps since the mapping is trivial and obvious, you might have a point. – Beefster Nov 11 at 20:58 • Maybe a good name would be "Traveling Wordsmith Problem" – Beefster Nov 14 at 16:21 # Metagolf: Catlike Piet The goal of this is to write a catlike program, which would be executed (in a Unix environment, though you needn't stick to that) by the following: yourprogram < file > output piet output  where piet output writes the contents of file to stdout. That is, you're to generate a Piet program which prints the input to yourprogram. One-liners Straight line programs can be written in Piet... in straight lines. If you're willing to take a hit to your score, your output can take the form of a string of commands: = none (continue color block) | push ^ pop + add - subtract * multiply / divide % mod ~ not > greater . pointer \ switch : duplicate @ roll  input number ? input character # output number ! output character  which is trivial to convert to a Piet program with the following (partially golfed) Python code: def P(s): h=v=0;l=len(s)+1;R="P3 %i 2 255 192 0 0 "%(l+2) C=[1,3,2,6,4,5];V=[0,192,192,255,0,255] for x in map("=|^+-*/%~>.,:@?#!".find,s): C=C[x//3:]+C[:x//3];V=V[x%3*2:]+V[:x%3*2] for i in [1,2,4]:R+="%i "%V[(C[0]//i)%2] return R+"255 "*4+"0 0 "+"255 "*l*3+"255 0 0 "*2  The dimension of said program is (n+3) x 2 if there are n characters in the string. Scoring Your code will be judged on the maximum dimension of the images that it outputs. • Part 1: Take the maximum score taken over all ascii codes (that is, single-character inputs), discounting EOF. • Part 2: Take the score for the input "Hello. My name is Inigo Montoya. You killed my father. Prepare to die." Your score is the product of the scores in part 1 and part 2. Punishment: Double your score if you write one-liners as above (that is, if you don't output an image). Bonus: If your program is written in Piet, take the square root of your score above. • It took me a while to understand the task as "Write a program taking INPUT which produces as output a piet program that takes no input but produces INPUT." I think it is a interesting and challenging, but it's reception will depend entirely on how many people are willing to learn/futz-around-in/deal-with piet. And I have no feel for how many that is. – dmckee Jul 7 '11 at 3:12 • @dmckee; would it be better if I just used a reduced instruction set, and only ask for the instruction stream? I think this is still challenging with {push 1,duplicate,add,subtract,multiply,output}. Come to think of it, if I restrict to {push 1,duplicate,add,output}, there's a reduction to some awesome algorithms. – boothby Jul 7 '11 at 4:48 • I did this in piet some time ago: craigoclock.blogspot.com/2011/05/metaprogramming-in-piet.html – captncraig May 21 '12 at 18:31 • Hello! This looks like a good but abandoned meta post, would you be willing to offer it for adoption? (If you want to, you can still post to main.) – programmer5000 Jun 9 '17 at 15:22 ## Chess move The Challenge Write a program that gets a string containing a chessmove and a chessboard as input, and then outputs the chessboard. Requirements The chess move will have this format: <from square><to square>[<promoted to>]  Examples: d2d4 f8g7 a7a8R  The chessboard format is not fixed, but there must be a 1 to 1 relation between the board and the string to represent the board. Also the format of the input must bet the same as the format of the output. Two suggestions of what it could look like: rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR rnbqkbnr pppppppp 00000000 00000000 00000000 00000000 PPPPPPPP RNBQKBNR  It is not required to store anything except the location of the pieces, and validity of moves can be assumed. Scoring Base score is character count (assuming your program can move pieces for all moves) Bonus multipliers: • If the program updates the promoted piece, divide by 2 • If the program also moves the rook when castling, divide by 2 • If the program also removes the pawn when capturing en passent, divide by 2 The moves, and castling & en passent in particular are explaned on Wikipedia. So basically writing a 100 character solution for the base problem gives the same score as an 800 character solution with all bonus multipliers. Examples If you would choose to use one of the board formats above, your input would look like one of these strings: e2e4 rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR e2e4 rnbqkbnr pppppppp 00000000 00000000 00000000 00000000 PPPPPPPP RNBQKBNR  Your corresponding output string would then be one of these: rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR rnbqkbnr pppppppp 00000000 00000000 0000P000 00000000 PPPP0PPP RNBQKBNR  • Before I get on to more specific criticisms: as presented, without the bonus this is too trivial to be interesting. I suggest removing some flexibility: require Fen notation for the board position and algebraic notation for the move, and making the current bonus options mandatory. On specifics: it's not clear why you talk about storage; and the board position notations you suggest don't include enough information to know whether en passant is possible. – Peter Taylor Dec 22 '13 at 23:56 • @PeterTaylor I agree that compared to chess programs this may be trivial, but I would like to make it a golf challenge. Compared to the hot code golf questions this is quite elaborate already in its basic form. (For a good solution the board design may need to be changed drastically). It is true that there is no attention to the legality of moves (whether it is possible to capture en passent) but for a mere viewer this is not required so I am not too worried about this. So far the chess questions seem to get very few answers as they tend to be complex and I hope to offer relatively easy entry. – Dennis Jaheruddin Dec 30 '13 at 11:02 • Your point about en passant is valid - you had said in the spec to not worry about legality. I'll try to convince you of my first point: without the bonus, this reduces to: a) parse first four characters into (col 1, row 1, col 2, row 2); b) take board as a 64-char string; c) board[8*row_2+col_2] := board[8*row_1+col_1]; board[8*row_1+col_1] := ' '; print board. This is trivial compared to any good golf question. (Note that the hot questions at the moment are neither golf questions nor good questions). – Peter Taylor Dec 30 '13 at 12:14 • This sandbox post has had little activity in a while. Please improve / edit it or delete it to help us clean up the sandbox. Due to community guidelines, if you don't respond to this comment in 7 days I have permission to vote to delete this. – programmer5000 Jun 9 '17 at 15:40 # Black Box Your task is to analyze a given situation for the game Black Box. Given a sequence of guesses and answers, your program is to either print the solution or suggest the next move. ## The game The board consists of 8×8 cells, with edges labeled like this: I'll probably create nice images here, particularly to make sure that the squares of the board are really square.  abcdefgh i I j J k K l L m M n N o O p P ABCDEFGH  The player shoots rays into the interior of the box, where they might get deflected, reflected or absorbed. He is told the position where the ray leaves the black box again, and from that has to deduce the positions of 4 atoms inside the black box. I'll have to include more of the game rules here, but for now see Wikipedia. # Input and output Input is a sequence of line, each consisting of two characters. The first denotes the point where the ray of light enters the black box, the second the place where it comes out again. In the case of a reflection, both characters will be equal. In the case of a hit, the second character will be -. If the input is enough to fully determine the locations of the atoms, then output should be four lines giving the coordinates of each atom. The lines should be two lower case characters each, the first giving the row and the second giving the column of the found solution. The atom positions must be printed in lexicographical order. If the input is consistent with more than one set of atom positions, then the output should consist of a single line containing a single character, which is the location where the next ray should be shot. That location has to be chosen in such a way that it can help find the solution. This is the case unless all of the atom positions consistent with the input so far would produce the same output for this next ray as well. Your output has to be terminated by a newline character. # Examples Let's take the atom configuration the Wikipedia article uses as an example as well:  abcdefgh i I j J k O O K l L m M n O N o O p O P ABCDEFGH  If the input were cf D- Em HH Co  then the output should be kb kg nd pg  but if the input were only Em HH  then the output might be for example K  ## Scoring This is code golf, so shortest answer wins. However, I'll only accept answers which are practical in so far as they compute their result in reasonable time. I'd say no more than five minutes on my system where I'll evaluate the answers, and I'll simply hope that correct solutions will be much faster and incorrect ones much slower, so that the speed of my system doesn't make a difference. A submission which gives a wrong answer for one of my test cases will be disqualified until it gets fixed. I will probably point out the problem in a comment to that post. # Create a program with "exact repetition" in its source code The task is to create a program, with the following restrictions placed on the printable ASCII characters in the source code: choose some k > 0. • Every non-alphabetic character has to appear exactly k times. • Every alphabetic character has to appear at most k times. • This rule differs from the former in order to avoid boring dummy identifiers while still making it a challenge to choose good library functions to call. Character set definitions used: • Non-alphabetic characters are !"#%&'()*+,-./0123456789:;<=>?@[^_{|}~ and '' (backtick).
• Alphabetic characters are ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz.

Note that no restriction is placed on characters outside of the range of printable ASCII characters (including control codes, tabs, newlines, higher unicode codepoints, etc).

What the program does is up to you; be creative. Some general guidelines:

• Programs that do something interesting might have better chances, although more impressive code structure (i.e. fewer comments) is also beneficial.
• Stuffing excess characters in comments is boring, and should be avoided/is discouraged.
• Dead/no-op code isn't terribly interesting either, but is probably unavoidable and at least has to conform to the language's grammar.

This is : whatever has the most upvotes at Feb 1, 2014 gets accepted as the winner.

#
#
/*@*/_[]={9.};main() {printf("He%clo \
world!%c\
",2^7&!8.&~1|~-1?4|5?0x6C:48:6<3>2>=3<++_[0],'@'^79-5);}


Prints "Hello world!" (adapted from an answer to another question). Probably wouldn't score a lot (since what it does isn't terribly interesting). Each of the non-alphabetic characters appear exactly twice, and no alphabetic character appears more than twice.

For meta: I want to post this, but I'm worrying that "do something interesting" might give too little guidance and the question won't receive many answers.. thoughts? Is it good as-is, or should I come up with some task that one should be required to implement (and possibly change the ruling to code-challenge, with length + 2^(characters-in-comments) as the score)?

## DIM, the DIM Integer Machine

The DIM Integer Machine is an engine for producing integer sequences.

It has one major problem: To put it mildly, it's kind of...dim.

After producing a single number, it immediately forgets what sequence it was working on. The only thing it remembers is the last number it produced and the current direction of the search, either ascending or descending. (And of course, it remembers the methodology for finding numbers according to the commands it understands).

Consequently, the user is free to change their mind after each number by issuing a new command.

Suppose the DIM has just produced an integer square: 81

• User inputs P and submits the input.
• DIM understands that P is requesting the next prime number after 81
• DIM computes and returns 83.
• DIM forgets what it was doing.
• User inputs O.
• DIM understands that O is requesting the next odious number and returns 84.
• DIM forgets what it was doing.

The DIM functions only for numbers between 1 and 1,000,000. If the DIM reaches either extreme while performing a search it will reverse direction and continue searching.

(For example: If searching in ascending order for a prime when the last number was 999,999, it will encounter 1,000,000 which is not a prime, then switch to descending order and continue searching for the "next" prime by moving downward - 999,999...999,998, etc.)

The DIM remembers the last number as 1 when it is first activated for a searching session.

This is the full list of commands that the DIM understands:

• P - Next prime number
• S - Next square number
• F - Next Fibonacci number
• O - Next odious number
• W - Next wasteful number
• U - Next undulating number
• K - Next katadrome
• R - Reverse direction immediately; the next command will proceed in the new direction

Because the DIM is so...dim, it absolutely DOES NOT precompute lookup tables of numbers in these sequences. It is far too forgetful for that to work. The DIM also has no Internet connection, so it is unable to consult the Online Encyclopedia of Integer Sequences or other such sites. It also has a sense of pride, so it does not make use of built-in Fibonacci functions or NextPrime / PrimeIndex / PrimeTest type functions.

Given the parameters it knows - a starting number, a search direction, the type of number to find - it simply computes the next number by some means other than mere data retrieval.

The DIM may accept input interactively, or from a newline-terminated text file, or from a pre-initialized array. You may not pack extraneous data other than the command sequence into the input - play fair!

This is a code golf, so least number of bytes wins. Submit your program with output results for the following search sessions:

1. P O U R F O R U S O U R P R O W S
2. W O R K F O R P O O R F O R K S K O O P S R O O K S F O U R W O W S
3. P O O P O O P O O P P O O P P R O P S P R O W S P O R K S

It is assumed that you know what prime, square, and Fibonacci numbers are. A brief explanation of the other integer sequences follows.

Odious - a nonnegative number which has an odd number of 1s in its binary expansion. The first few odious numbers are 1, 2, 4, 7, 8, 11, 13, 14, 16, 19

Wasteful - a natural number that has fewer digits than the number of digits in its prime factorization (including the exponents). The first few are 4, 6, 8, 9, 12, 18, 20, 22

Undulating - has alternating digits of the form aba, abab, ababa, etc. Assume all U numbers are non-trivial, i.e. 3 digits or more. The first few: 101, 121, 131, 141, 151, 161, 171, 181, 191, 202, 212

Katadrome - A number whose hexadecimal digits are in strict descending order. The first few are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 32, 33, 48, 49

• When I post the question, I'll also include external links to MathWorld or OEIS for those who need more detail on the less familiar sequences, but the explanations above should be sufficient for most, I think. – Jonathan Van Matre Mar 6 '14 at 23:28
• Your definition of "undulating" isn't the one I'm familiar with, which just requires that the digits alternately increase and decrease. Also, it would be better to include expected answers for the test cases, so that submitters can use them as test cases rather than them serving just for you to say "No, this is buggy". – Peter Taylor Mar 6 '14 at 23:57
• Yes, that's my plan, I just haven't finished double checking my results for the test cases yet. OEIS and Mathworld have the strict 2-digit definition of undulating, but I'll make sure to make the definition here more prominent so it is clear which interpretation is meant. – Jonathan Van Matre Mar 7 '14 at 0:04
• Hello! This looks like a good but abandoned meta post, would you be willing to offer it for adoption? (If you want to, you can still post to main.) – programmer5000 Jun 9 '17 at 16:09

# Efficient Testing for Armstrong Numbers

An Armstrong Number (also known by different names, including Narcissistic Number; see Wikipedia for more information) is a non-negative number (for our purposes represented in base 10) that is equal to the sum of the individual digits of the number each raised to the power of the number of digits. For example:

2. The individual digits are 4, 0, & 7.
3. Since it is a three digit number, we raise each digit to the third power: 64 (4^3), 0 (0^3), & 343 (7^3).
4. The sum of those values is 407 (64 + 0 + 343).
5. Because the final sum is equal to the original number, it is an Armstrong Number.

By contrast:

2. The individual digits are 4 & 7.
3. A two digit number, so raise each digit to the second power: 16 (4^2) & 49 (7^2).
4. The sum of those values is 65 (16 + 49).
5. The final sum of 65 is not the original number, so it is not an Armstrong Number.

Your mission, should you decide to accept it: Write a program in any programming language (using only standard language features and libraries) implementing the most efficient algorithm possible to test the numbers from 1 through 18,446,744,073,709,551,615 (264-1) inclusive for "Armstrongness", generating a list of Armstrong Numbers, and only Armstrong Numbers, as output.

While any language is acceptable, it should be obvious that interpreted scripting languages will be at a disadvantage in the efficiency department. That being said, a superior algorithm in an interpreted scripting language can beat the pants off an inefficient algorithm in hand tuned assembly language.

## Winning Criteria

The algorithm that can check all possible candidate numbers for "Armstrongness" in the least amount of time on a reference computer will be the winner. The reference computer will have the following specifications: {approximately an AMD Phenom class computer with 8 GB RAM running Windows 7 Ultimate 64 bit}

• I don't know that this would belong in the (already very long, maybe too long) problem statement above, but other historical background. The class was for Fortran 77, and I was in a friendly competition with my TA to write the shortest version. I never could win that one, so I decided to write the most efficient version instead. Hence: I prefer efficiency puzzles to code golf (though code golf is fun too). – CasaDeRobison Feb 20 '14 at 8:30
• This doesn't seem to have an objective winning criterion. You do list "criteria I'll be using to judge this", but a) it mixes specification with winning criteria; b) it combines factors without indicating their weight. – Peter Taylor Feb 20 '14 at 11:51
• The question also seems to be about twice as long as it needs to be. If you use the [link text](url) link notation you can shorten it slightly; you can also lose paragraphs by cutting the worked example and brute-force code (link to the existing question on narcissistic numbers instead); cutting the waffling about which languages you think have advantages; and simplifying the motivation. – Peter Taylor Feb 20 '14 at 11:57
• I think efficiency problems are not well suited to code-golf. The efficiency of an algorithm depends on too many factors. You could perhaps require the lowest number of power operations. – ugoren Feb 20 '14 at 12:43
• @ugoren, 0 is easily obtained. – Peter Taylor Feb 20 '14 at 12:57
• @PeterTaylor, You're right. Still, trying to replace a time measurement with the number of operations of a certain type sometimes helps define the problem better. – ugoren Feb 20 '14 at 15:12
• @PeterTaylor: I agree it is quite long, and will consider revisions to it. – CasaDeRobison Feb 20 '14 at 21:43
• @PeterTaylor: I'm open to better phrasing of the "objective winning criteria" but really, it is pretty objective already. One, no wrong answers allowed in the winner. Two, how efficient is the algorithm (based on the range of numbers tested and time taken to test them). For example, an algorithm that tests all numbers through 9 digits in 100 seconds is faster than an algorithm that takes 20 seconds to test all numbers through 8 digits (10 times larger interval in only 5 times the time). How might you suggest integration of this with the problem statement? – CasaDeRobison Feb 20 '14 at 21:48
• @PeterTaylor: Glad I included the disclaimer about failing eyesight, given that I searched for narcissistic numbers and came up with nothing. I either searched the wrong portion of PCG (meta) or I made a typo when spelling narcissistic. – CasaDeRobison Feb 20 '14 at 21:49
• @ugoren: efficiency may not be suited to code golf, but my understanding was that this 'forum' was about "programming puzzles" and "code golf". I certainly would consider finding a more efficient algorithm to be like solving a puzzle, though maybe I'm alone in that, in which case no biggie. – CasaDeRobison Feb 20 '14 at 21:51
• Edited the problem statement (which is still admittedly quite long, still considering other edits) by removing the final PPS paragraph and replacing the existing links as suggested. – CasaDeRobison Feb 20 '14 at 21:59
• The winning criterion is still too imprecise IMO. (NB Of the judging criteria you list, the first is part of the spec, so it's an acceptability criterion rather than a winning criterion). A genuinely objective winning criterion allows me to calculate my score before I submit my answer. – Peter Taylor Mar 12 '14 at 8:47
• It should be much shorter in order to not discourage people from approaching your challenge. Almost all the text after the definition doesn't add anything to the challenge - beside "don't print wrong numbers" which is of course relevant. I also think that a more precise criterion should be given instead. – Howard Mar 12 '14 at 9:03
• I've posted a "radical" update to it. I suspect the new winning criteria will not be acceptable either, since it involves a "reference computer" for final timing. Very open to suggestions on how to restate it so that a crappy algorithm on fast hardware doesn't beat an efficient algorithm on slow hardware. – CasaDeRobison Mar 12 '14 at 20:17
• The possibility that processor architecture or available memory affects the results is a tricky issue with fastest-code questions, but there isn't really a better way of comparing speed of programs than measuring on a large test case. I can at least measure how my program compares to someone else's on my computer, and know whether it's close or not. – Peter Taylor Mar 12 '14 at 21:23

## Amino Acids Matcher

In genetics, a codon is a set of three nucleotides, the most basic form of nucleic acids. A codon "codes" (no pun intended, that's the actual term used) for a specific amino acid. Given a string of DNA, it is converted into RNA form by taking the opposite complementary pair.

DNA    RNA
A      U (T changes to U)
T      A
C      G
G      C


You will be given a String of unknown length that contains multiple codons. You must convert them to RNA form and print out the amino acid for each. See here for a chart: http://en.wikipedia.org/wiki/RNA_codon_table#RNA_codon_table

## Sample Input

TACTCGGATACT

Is split into

TAC, TCG, GAT, ACT

We now change each letter to its reciprocal

AUG, AGC, CUA, UGA

And print out the amino acids

Methionine, Serine, Leucine, Stop

This would probably be

I know that this is most likely not sufficiently explained and might be too complicated. Additional, tell me if there is any incorrect information above.

• So basically this is a challenge to compress a lookup table. You should probably specify that the string will be a multiple of three characters (or specify what to do otherwise); and it would seem sensible to inline the lookup table so that a) the question doesn't rely on the external page remaining intact; b) you save everyone who wants to answer the question the hassle of calculating it. – Peter Taylor Mar 17 '14 at 12:42
• Thanks for the feedback. I'll update accordingly later today. – nrubin29 Mar 17 '14 at 15:48

# Create a calendar

We all know HDD-space is precious and bandwidth is expensive, therefore it is best to reduce the size of your executables. Let's start with your calendar:

Your task is to build a calendar app in at most 512 bytes. The calendar must at least support the following features, but additional features may gain you additional upvotes:

• It must be able to show the current month with the current day highlighted
• The user must be able to find out the week day of each day

Rules:

• Maximum code length is 512 bytes (counted as UTF-8 without BOM)
• You may subtract the bootstrapping code (i.e. int main(int argc, char **argv) in C or <?php in PHP) and imports from the final size to allow for more verbose languages to be in
• You may use standard time / date functions of your programming language, as long as they don't allow you to output a ready to use calendar
• No network access (I said bandwidth is expensive!)
• Voters decide on the amount of features / look and feel / creativity

This needs a tag for the size restriction, any suggestions?

• "bandwidth is expensive" <sup>[citation needed]</sup> – John Dvorak Mar 22 '14 at 5:27
• Seems rather close to Output: Calendar Month – Peter Taylor Mar 22 '14 at 5:33
• Who decides what counts as bootstrapping code? It seems odd to arbitrarily exclude code like that, and the examples you gave can be golfed a lot: they're more or less equivalent to main(){ and <? ` respectively. – Wander Nauta Mar 24 '14 at 20:49
• @WanderNauta Bootstrapping code is the code that's essentiell to get a working noop program. – TimWolla Mar 24 '14 at 21:00
• @TimWolla That definition won't fly. A zero-byte file is a working noop PHP script, for example. – Wander Nauta Mar 24 '14 at 21:01
• @WanderNauta A zero byte file is a working noop in every language. – TimWolla Mar 24 '14 at 22:12
• So what's bootstrapping code then? :) – Wander Nauta Mar 24 '14 at 22:53
• for the limit I'd say code-shuffleboard or restricted-source – Einacio Mar 26 '14 at 15:57
• This sandbox post has had little activity in a while. Please improve / edit it or delete it to help us clean up the sandbox. Due to community guidelines, if you don't respond to this comment in 7 days I have permission to vote to delete this. – programmer5000 Jun 9 '17 at 16:28