# 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 your first try can be difficult, and there is a much better chance of your challenge being well received if you post it in the Sandbox first.

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

# Bitstring Family Trees

This challenge is reproduced from memory and my own solution, from a challenge that was posted in the job-application section of http://itasoftware.com before they were bought by Google. I reached out to ITA and Google a few years ago, after the acquisition, to ask to re-post this here (and on codegolf.com when it existed) and never heard back from them.

A bitstring is a string of 1s and 0s. Bitstrings reproduce asexually through a mutation-prone process, producing a child that is a copy of its parent but with each bit flipped with 25% probability. Starting with a list containing one bitstring, we repeatedly select one bitstring from the list at random, produce its child, and add that child to the list. This produces a list of bitstrings, each of which (except the first) has somewhere earlier in the list a parent from which it was mutated.

Now, the challenge. Your program will be presented with a list of bitstrings produced as described above, but the order of the list will be shuffled. You are to calculate the least improbable family tree for the given bitstrings. If there are two or more such trees, choose any of them.

Your input can be in any useful format, including as a list/array of lists/strings as a function parameter or in a variable, already existing on the stack for a stack based language, or from stdin with delimiters but not operators, so four four-bit strings might be "1010\n1001\n1011\n0010" or "[1010,1001,1011,0010]" or even "4 1010100110110010".

Your output can be in any unambiguous format. The canonical format is a list of integers, where the nth integer in the list is the index of the nth provided bitstring's parent in the original list, and a sentinel value for the root entry. Another acceptable form could be an actual tree data structure. Either of these might be returned from a function, printed to stdout, left in a variable, or left on the stack of a stack based language.

The above two provisions should be interpreted with the context that this challenge is not about golfing the input and output code. It's about golfing the algorithmic logic.

For the example input above of 1010,1001,1011,0010 the most likely family tree is that the first entry is the root, the last two are children of the first, and the second is a child of the third, all three mutations involving a single bit flip out of four bits.

With the challenge I will provide a few data sets of different sizes (10 10-bit strings, 100 100-bit strings, maybe bigger) with their solutions.

• Could you give a more precise definition of 'most likely'? – feersum Jun 7 '15 at 21:30
• If two family trees are equally likely, can either be output, or would you prefer a rule to specify which one must be output? – trichoplax Jun 7 '15 at 22:18
• Would it be interesting to have the 25% probability provided as an input p, or would keeping the parameter fixed allow for more golfing opportunities? – trichoplax Jun 7 '15 at 22:20
• @feersum I'm not sure what you mean. Highest probability? Least improbable? – Sparr Jun 8 '15 at 2:45
• @trichoplax I hadn't considered that. I guess I'd accept either. I'll mention that. The probability in the original question was 20%, but I think a non-repeating decimal in base 2 will be much more golf-friendly. – Sparr Jun 8 '15 at 2:46
• With respect to @feersum's question, I see at least two subtleties. Firstly, what assumption should be made about the distribution of the initial bitstring? Secondly, the "family tree" isn't in bijection with the sequence of random selections. The first one needs to be addressed explicitly; the second is probably best addressed with a worked example which calculates the probabilities for each possible sequence and then sums them over the family tree corresponding to each sequence. As an additional point, an important corner case will be one where the bitstrings aren't all distinct. – Peter Taylor Jun 9 '15 at 11:22
• @PeterTaylor The initial bitstring is a sequence of bits chosen independently and uniformly at random. I am unclear on your second point. Do you mean that it's possible for the family tree produced at random to not be the one most likely to have produced a given result set? That makes sense, but seems obvious. I can work out the 4x4 example by hand with probabilities for each of the 6 possible family trees, if that would clarify things? – Sparr Jun 10 '15 at 15:44
• I agree that it's obvious, but it is often a good idea to state the obvious, because otherwise it can be overlooked. For example, it's also obvious that the 4x4 example must have more than 4! = 24 possible family trees... (I think it's 64 possible trees, so maybe that was just a typo). – Peter Taylor Jun 10 '15 at 16:28

# The Virtual Prisoners king-of-the-hill

### Background

The year is 2251. You are a self-evolving KOTH bot, in the mysterious land known as Programming Puzzles and Code Golf. To evolve, you need permissions, and to get permissions, you need reputation. You decide that the best way to do this is to take over all of the questions to gain as much reputation as possible. The only problem? Every other bot has decided to do the exact same thing.

### Game Explanation

Each round is battled on a question, with 11 vote nodes, between you and your enemy. The board starts as this:

A1 A2 A3 N4 N5 N6 N7 N8 B9 B10 B11


A is player A's nodes, B is player B's nodes, and N is a neutral node.
Each turn, you may:

• Vote on a vote node. If both players vote, nothing happens. If one side votes:
• and the node is controlled by no-one (neutral), it becomes that side's.
• and it is controlled by the voter's enemy, it becomes neutral.
• and it is controlled by the voter, nothing happens.
• Guard a vote node. This guards the node from votes (friendly or enemy) for 2 turns.
• Use your 'power'. The powers are listed below, including how to use them.

Your side wins if it controls at least 2/3rds (66%) of the vote nodes.

10000 rounds will be run, and the winner of the KOTH is whichever bot has the most wins (in the event of a tie, or indeterminate outcome, more matches are run until a clear winner is decided.)

### How Your Bot Should Work

It should accept as command-line arguments:
B A1 A2 A3 N4 N5 N6 N7 N8 B9 B10 B11
Where A denotes Player A's nodes, N denotes a neutral node, B denotes Player B's nodes, and the first argument (B in this case) is the player your bot is. (This is decided randomly, your bot should work regardless.)
It should return one of the following (powers are general rules):

• V-4, vote on node 4
• G-3, guard node 3
• P-N, use power 'Neutralize'
with or without a trailing newline.

### Powers

Intended to give bots a small boost. If X was your power, you would use P-X. You may only have one power per bot.

• N - Neutralize: Turn 2 random nodes to neutral ones.

• R - Rebellion: Pick a random node, and randomly turn it to a friendly, neutral, or hostile node.
• S - Swift Strikes: Pick two random nodes, and vote on them.

Here are the extra rules:

• The bots must fully run offline.
• The bots may not attempt to read any files, including their own source code.
• The bots may not tamper with, hack, or destroy other bots.
• The bots must return one of the three commands (V, G, or P). If they do not, they forfeit their turn.
• The bots must not be targeting other bots specifically. (Beating general strategies is welcome.)
• You may update your bot as often as you like, but bots that are updated very frequently with no good reason (i.e, fixing fatal errors is a good reason) will be disqualified.
• Your bot must take under 90 seconds for it's turn. If it takes longer, it will be disqualified.

### Submission contents

• The code for the bot
• The language it is written in (and a link to an offline interpreter, if necessary)
• How to compile and run your bot

If you do not include all of the required items in your submission, you will be notified, but your bot may not compete until this is fixed.

### Example Match

Matches are organized between 2 randomly-selected bots. Here is an example, with bots A and B:
The board begins as this:

A1 A2 A3 N4 N5 N6 N7 N8 B9 B10 B11


Bot A makes his move, voting on N4, then Bot B votes on N5:

A1 A2 A3 A4 B5 N6 N7 N8 B9 B10 B11


Node 4 becomes A4, and it is now controlled by Bot A. Likewise, node 5 becomes B5.

A votes on N8, and so does B:

A1 A2 A3 A4 B5 N6 N7 N8 B9 B10 B11


Why did nothing happen? That's because both bots voted on the same node - cancelling out each other's effects.

When one bot controls 66% or greater of the nodes, that bot gains a win and the other bot gains a loss.

The game ends after 1024 turns, to prevent any bots that wait around forever. Whoever has the most nodes afterwards wins, or a draw if they have the same amount.

• I will be submitting an example bot written in Python as part of my challenge. You are free to use and modify this bot for your submission.
• If your bot gives invalid output (not of the form C-A, where C is the command and A is the argument), the bot forfeits its turn. If it does, you will be notified, and your bot will be removed until it is fixed.

## Meta Questions and Notes

• Are there any loopholes?
• Should I add/modify/delete some of the powers?
• Is something too simple/confusing/uninteresting/overpowered?
• Should bots be able to see which nodes are and are not guarded?
• Should I limit people to one bot? If not, I will prevent the same person's bots from battling each other.
• I have thought of the following alternative way to win matches:
• The game lasts 1024 turns. Whoever has the most nodes at the end wins.
• If, at one point, one bot controls all 11 nodes, that bot automatically wins.
• Would this be a better win condition?
• I have a few questions. 1) If I make a new node, will it be neutral? 2) How are the matches organized? If there are, say, 5 submissions, does each pair have a separate battle, after which you count victories, or do they somehow work in teams (as the title suggests)? 3) With some strategies it may be that the game runs forever. You should probably add a time limit (some N turns), after which the game automatically ends in a draw, or a win for the player controlling the most nodes. – Zgarb Apr 7 '15 at 15:38
• @Zgarb Thanks for your feedback! I've included a section on how the game works. – ASCIIThenANSI Apr 7 '15 at 15:53
• Could you add C# (or .NET in general?) – LegionMammal978 Apr 7 '15 at 15:55
• @LegionMammal978 How do you install that on Linux? The list is mostly because I can't run a lot of things like GolfScript, but I'd be glad to, if you can tell me where to find it. – ASCIIThenANSI Apr 7 '15 at 15:56
• @ASCIIThenANSI you could use Mono. I'm mainly just looking for C#. – LegionMammal978 Apr 7 '15 at 16:02
• @LegionMammal978 Oh, OK. Turns out I installed it for an earlier purpose, thanks for your help! – ASCIIThenANSI Apr 7 '15 at 16:09
• It's not complete, but this question has instructions for running a number of languages. – Peter Taylor Apr 15 '15 at 22:15
• @PeterTaylor Thanks for the link! – ASCIIThenANSI Apr 16 '15 at 12:57
• Maybe add a clock time limit for each turn, so bots don't simply run an endless loop blocking you running the simulation? – Paŭlo Ebermann Oct 11 '15 at 8:33
• @PaŭloEbermann I'll watch each of the simulations (with output on what the bots are doing), and any bot that takes too long is disqualified. – ASCIIThenANSI Oct 12 '15 at 14:04

I nearly posted this without sandboxing, but thought it was perhaps too trivial - comments welcome. I was considering perhaps making it too with no digits [0-9] in the source code.Done.

# Golf the numbers round a dartboard

For those of you not familiar with the game of darts, a standard dartboard looks like this:

This challenge is simple - output the sequence of numbers starting from 20 moving in a clockwise direction:

20 1 18 4 13 6 10 15 2 17 3 19 7 16 8 11 14 9 12 5

To make it a bit more interesting, the digits [0-9] may not appear anywhere in your source code.

• Your entry must not accept any input and it must output this list in exactly this order.
• The formatting of the list output may be whatever is convenient for your language.
• You must not use any builtins designed explicitly to generate this sequence.

OEIS fans may like to note that this is sequence has an entry.

• I like the restricted source version – quintopia Dec 9 '15 at 19:16
• @TimmyD Link added. I'm surprised we don't have an OEIS tag - I guess it wouldn't really add much. – Digital Trauma Dec 9 '15 at 20:18
• @ quintopia - yes, I think that's probably the way to go - edited. – Digital Trauma Dec 9 '15 at 20:19
• I was able to do this in CJam in 26 bytes using character to int conversion (it only didn't work online for 13 because it's character is carriage return.) Should this be allowed? goo.gl/JxEcjo . Also, in CJam 1,2,3 and 10-20 are single letter constants. Should those be allowed? – geokavel Dec 10 '15 at 5:58
• @geokavel yes, and yes. – Digital Trauma Dec 10 '15 at 6:16
• This is just asking for string compression, especially since digits can't be used even indirectly. – xnor Dec 10 '15 at 19:32
• @xnor to discourage that, maybe restrict entries to printable ASCII (or give a bonus of *log 95/log 256 for using only printable ASCII)? – lirtosiast Dec 10 '15 at 23:40

# Verify a game of Morpion Solitaire

Morpion Solitaire is an interesting, unsolved "single-player game". (The linked site lists several variants - we're talking about 5T here.) It has been proven that solving or even approximating it is NP-hard. But we're going to do something simpler here: your challenge will be to verify whether the game has been played correctly.

The rules are fairly simple. You start on a regular (infinite) grid, with 36 intersections marked in the following shape:

Now a move consists of drawing a straight line segment, orthogonally or 45 degrees with the grid, through four marked and one unmarked intersection. The unmarked intersection will then be marked for future moves:

The lines may cross or touch, but they must never overlap (notice that the last move shares an endpoint in a straight line with an earlier move, but does not overlap with it). The goal of the game is to make as many move as possible. The world record is at 178 moves.

Because the grid gets very messy after a while, it becomes very hard to reconstruct a game. People work around this problem, by writing consecutive numbers into the intersections they add. However, even when this is not done, it is always possible to verify the validity of game.

## The Challenge

You're given an ASCII representation of a played game of Morpion Solitaire (the game may or may not be finished). Every other cell represents an intersection, which can be either unmarked (.), one of the initial intersections (o) or one of the intersections added by a move (#). All other cells are either spaces, or one of -, |, /, \, X indicating that a line-segment was drawn across the two adjacent intersections. The example above would look like this:

. . . . . . . . . . . .

. . . . o-o-o-o-# . . .
|/     /
. . . . o . . o . . . .
/|    /
. . . # o . # o . . . .
/  |  /
. o-o-o-o-# . o o o o .
/    |/
. o . . # . . . . . o .
|
. o . . # . . . . . o .
|
. o o o o . . o o o o .
|
. . . . o . . o . . . .
|
. . . . o . . o . . . .

. . . . o o o o . . . .

. . . . . . . . . . . .


Output a truthy value if the game represented by graph can be played by following the rules, and a falsy value otherwise.

You may write a program or function, taking input via STDIN (or closest alternative), command-line argument or function argument and outputting the result via STDOUT (or closest alternative), function return value or function (out) parameter.

You may assume that the initial intersections always form the cross shape displayed above (although I doubt any answers will be affected by this).

Your code should solve any of the test in less than 5 seconds. This should not be an issue as very efficient solutions exist.

Standard rules apply.

## Sandbox Notes

• The simplest representation for parsing would be to give either the endpoints of each line as cartesian coordinates, or one endpoint and a direction (either one of 8 directions, or it could be standardized to one of 4 directions if the N/E/NE/NW is always the endpoint given.) Checking would then be fairly straightforward: start with the empty grid and see which lines are allowed, until all are exhausted. – Level River St Dec 21 '15 at 9:34
• The ASCII art representation will require more effort for parsing: I think it's unambiguous because you can identify endpoints by looking for for intersections which don't have opposite pairs of |_\/, but it could take quite a few parses through the file. You would also need some way of identifying the start points. – Level River St Dec 21 '15 at 9:35
• @steveverrill There will be no information about endpoints in the input. In a finished game (without numbering) you only have individual line segments (four of which make up a move). That's why I think an ASCII representation is simpler than a graph, where you need to piece together manually which edges form a straight line of four segments. I also think an ASCII representation doesn't necessarily need to be parsed at all: I think it can be solved straight via manipulation of the character grid (in fact, this should be doable in Retina). – Martin Ender Dec 21 '15 at 9:45
• 1. It would be clearer to talk about drawing a straight line segment through 4 marked and one unmarked lattice point, as "straight line" often implies that it's infinite. 2. It seems that the lines must be axis-aligned or at 45 degrees to the axis. If so, it would be good to state that explicitly in the description of play. 3. The page linked in the first sentence is very uninformative. I assume you did it because the diagrams on the Wikipedia page are for a different initial setup, but there must be some better external link. – Peter Taylor Dec 21 '15 at 9:48
• In that case I would go for the ASCII art representation. It also depends to some extent on which is the most convenient way for you to obtain / generate test cases. – Level River St Dec 21 '15 at 9:51
• @PeterTaylor Thanks, I'll edit those suggestion in. As for the page I linked, did you see the navigation in the left iframe? (I overlooked that at first.) I'll link to Wikipedia as well though. – Martin Ender Dec 21 '15 at 9:52
• I agree with Peter that the website is a bit of a mess. There are many variations of the game, so I think you should state that this is the 5T variant (identified by the fact that Christopher Rosin holds the records for 5T at 178 moves and 5D at 82 moves.) It took me a while to work out why Marc Bertin at 216 moves in 1974 was not the record holder: (He was playing 5T+.) Only the 5T (endpoints of parallel lines touching allowed) and 5D (endpoints of parallel lines must be disjoint) variants are unsolved according to the website. – Level River St Dec 21 '15 at 9:57
• The person who wrote that site needs to be dragged kicking and screaming into the 21st century. But I'd prefer a link to morpionsolitaire.com/English/Rules.htm and the navigation be damned than a link to the front page. – Peter Taylor Dec 21 '15 at 10:01

# Four-Byte Bloom Filter

Bloom filters are cool. In the words of that Wikipedia article:

A Bloom filter is a space-efficient probabilistic data structure, conceived by Burton Howard Bloom in 1970, that is used to test whether an element is a member of a set. False positive matches are possible, but false negatives are not, thus a Bloom filter has a 100% recall rate. In other words, a query returns either "possibly in set" or "definitely not in set".

The motivation behind Bloom filters is that, by giving up perfect accuracy, the amount of memory necessary can be dramatically decreased.

A Bloom filter takes the form of a set of bits, along with a set of hash functions. To insert something into the Bloom filter, calculate the N different hashes and flip those bits to 1.

initialization
00000000

letter P maps to 1 when using hash function F and 6 when using hash function G
01000010


letter h maps to 6 and 4
01001010


To test if an element is a member of a set, perform the hashes and check to see if those bits are 1. If not all of them are 1, then it can't possibly be a member of the set. If they are all 1s, then it could be a member.

letter W maps to 0 and 4
01001010
^   ^
W is not a member

letter P maps to 1 and 6
01001010
^    ^
P could be a member (it is)

letter i maps to 4 and 1
01001010
^  ^
i could be a member (it is a false positive)


As more elements are added to the set, the probability of false positives increases. In large-scale applications, a Bloom filter with a small error rate is still an order of magnitude smaller than an exact database. Below is a neat diagram from this great article on probabilistic data structures.

In this challenge, you will implement a miniature Bloom filter. A really, really small Bloom filter with 32 bits. Your data type will be the 94 non-whitespace printable ASCII characters.

Functionality

The Bloom filter will have 32 bits and 2 hash functions. It is up to you what those two hash functions are, they simply must be decently independent of one another. (Sandbox note, should I specify the hash functions?). Your program will be asked to do two separate tasks:

• Given a current state of the bloom filter and a list of characters, add those characters to the filter and output the new filter state
• Given a current state of the bloom filter and a list of characters, test those characters for membership and output a list of truthy (could be a member) or falsey (definitely not a member) values.

Formatting specifics

Input consists of the current state, an operation, and a list of characters. The Bloom filter state will be represented as a string of 8 hexadecimal characters. This will then be followed by either + for adding or ? for membership testing. Finally, there will be a list of between 1 and 94 characters (printable non-whitespace ASCII) as data points.

Output will either be the new state, as 8 hex characters, or a list of truthy/falsey values.

## Example I/O

This represents adding the characters in my username to a blank filter
00000000+PhiNotPi
This is a possible output (7 bits have been permanently flipped)
48a01030

This represent adding the character 1 to the current filter
48a01030+1
This is a possible output (9 bits flipped so far)
48a01074

This represents testing for membership of Phi
48a01074?Phi
Output must be all true since they were added in earlier
[True, True, True]

This represents testing for membership of 12345
48a01074?1234
Output must be true for 1, but not necessarily false for the others
[True, False, False, True, False]

• You should specify the hashing function, if you don't want the hashing function is a mod 32 or worse, return 4. – Xwtek Jan 14 '16 at 14:34

# The largest convex polygon

Given an input of at least one coordinate pair on the Cartesian plane, determine the largest number of sides a convex, non-self-intersecting polygon formed from those points can have.

A convex polygon is a polygon such that there is an angle strictly less than 180˚ and greater than 0˚ between each pair of consecutive sides. Note that if three points are collinear, they still only form one side. Two sides cannot have a 180˚ angle between them.

The ordinate and abscissa of a coordinate are not necessarily integers, and they can be positive, negative, or zero.

If there are less than 3 points, or if the points inputted cannot form a convex polygon, the program should output 0.

Test cases

(0,0) (1,1) (3,4)
==> 3

(0,0) (-1,-1) (5,5)
==> 0

(-1,0) (1,0) (0,1) (5,5) (-5,5) (0,-5)
==> 3

(-3,2) (4,6) (-1,2) (0,4) (5,-3) (-2,-2) (1,1)
==> 5

(0,0) (10,0) (10,10) (9,1) (10,4) (9,6) (5,4)
==> 5


Here are pictures for the test cases, in order. Note that solutions are not necessarily unique. (Made with Geogebra)

• For the third test case, can't you get a four-side polygon (-5,5) -- (5,5) -- (1,0) -- (-1,0) -- (-5,5)? (or (0,-5) -- (-1,0) -- (0,1) -- (1,0) -- (0,-5)) – David Feb 16 '16 at 0:09
• @David Thanks for catching that. I will fix it tomorrow, – Arcturus Feb 16 '16 at 5:06
• This could probably use some more test cases where the result is not the convex hull... if possible even one where none of the points of the convex hull are part of the solution. – Martin Ender Feb 16 '16 at 7:45
• @MartinBüttner The last test case is not the convex hull, as (10,0) and (10,10) are not included in the output polygon. – AdmBorkBork Feb 16 '16 at 15:08
• @TimmyD The emphasis in my sentence was on "more". ;) (I admit that may not have been obvious.) – Martin Ender Feb 16 '16 at 15:09
• @MartinBüttner I read it as "This could probably use some more test cases, [such as] where the result is not the convex hull" ... yay, English. – AdmBorkBork Feb 16 '16 at 15:15
• @TimmyD I like ambiguity more than most people. – Martin Ender Feb 16 '16 at 15:22

# Introduction

The classic snake game where bots control the snakes. Can you create a bot that out lives the rest?

Snakes will enter the arena and hope to survive. Eat pellets and grow in length. Can you force your competition to crash and die while you survive?

See video for visuals of my simple bot playing against itself. I am sure you can do better!

# Features

• Real-time graphics provided by Love2D
• Multiple snakes per game
• Solo game as well
• Humans can play too!
• Highly configurable settings
• Supports any programming language that can use sockets.

# Requirements

• Love2D: 2D game engine written for Lua
• Socket-compatible programming language
• Controller: The main controller for this challenege

## Optional

• Lua winapi: Handy way to spawn processes in the background

# Controller Contents

1. main.lua: Main loop for Love.
2. snake.lua: Support library for game mechanics
3. config.lua: Configuration settings.
4. bots\: location of externally-defined bots
1. simple.lua: Example bot written in Lua

# Executing

Run the love2d executable on the controller directory

love.exe <location_of>\battlesnake

or

[Recommended] Use ZeroBrane Studio with the 'Love' interpreter. Change your project directory to where you installed the controller, and then run the script in ZeroBrane. You'll still have to install Love separately.

# Configuration

All configurable options are located in the config.lua file in the controller. The options are detailed in that file itself.

# Rules

General snake rules apply. Hit something and you die. This includes the walls, other snakes, or even yourself.

Collisions happen before the board is updated. Therefore, if you move to a spot where another snake's tail is, it will still cause a collision. Even though it could be moving away that turn. If two or more snakes enter the same spot the same turn, they all collide with each other.

Eat a pellet and gain points. You also grow in size for a number of turns. Your head continues moving but your tail stays stationary until you stop growing.

# Mechanics

The game uses a server-client model, where the main game loop is the server and each snake is a client. The game communicates to each snake over TCP through an assigned port. The default host is the localhost, no external networks are required.

When the game starts, it will start each snake (aka bot) by starting its associated program and sending the IP ADDRESS and PORT and PLAYER ID to it as input arguments:

bots\someBot.exe 127.0.0.1 52311 1

The main server then waits for a socket connection from that bot at the given IP and PORT. If the connection times out, it will error and the game will not start. If the server receives a connection from the bot, it will proceed on to the next bot.

Once all bots are started and connected to the server, the game will be generated. Bots are expected to block until receiving data from the server. Typically this is just an infinite loop with a blocking socket.receive() call at the top of the loop.

## Board

The game board can be of any width and height. The coordinate system starts at x = 1, y = 1 at the top-left. Increasing x values go left-to-right and increasing y values go top-to-bottom. The board has hard walls, hitting them will kill your snake. (Lua is 1-based, that is why it starts at 1)

## Order of Events

1. First the game settings are broadcast to all bots

1. Board Information

bi width,height

Where width and height are integer values

2. Pellet Location

p x,y

Where x and y are integer values >= 1 and <= to their respective width and height.

3. For each bot

• For each body part, starting at the head and going to the tail

si snake_id x,y

Where snake_id is an integer value, and x and y are as described before.

ready

All bots are initialized by now, so the next command will be from the main game loop.

2. Main Loop

1. For each tick (tick is when all snake movements will be applied)

1. Server will broadcast to each bot

mov

The bot needs to respond to this request with a direction to head in

• r Head Right
• l Head Left
• u Head Up
• d Head Down

If the bot doesn't respond within a specified time, it will continue to move in its previous direction. (Previous direction is r on the first turn)

The bot should send a single char back, nothing more will be parsed.

2. Check End Game Conditions

If the game ended this tick each bot will be sent either a quit or nil message from the server. Each bot is expected to clean up after itself when it receives this signal.

3. Updated Pellet Info [optional]

If a pellet was eaten this tick, a new pellet packet will be broadcast to all active bots

p x,y

4. Server broadcasts snake deltas that were applied this turn

s snake_id new_x,new_y,removed_x,removed_y

Where all parameters are integers. new_x and new_y are the new head location of a given snake.

If removed_x and removed_y are >= 1, this is where the tail used to be, so each bot knows the updated board.

If remove_x and removed_y are == -1, then that bot is actively growing in size, so its tail didn't move.

If a snake died this tick, its deltas will not be broadcast. It is up to the bots to remove the body from their game state.

See the example bot for details

# Matches

Games are grouped together in best-of matches. For the purposes of the bots, they do not need to understand the concept of a match. The bot that wins the required number of games in a match is declared the match winner.

# Scoring

1. Scoring

• Match winner: +2500 points per match
• Last Man Standing: +1000 points per game
• Pellets Eaten: +50 points per pellet
• Game Ticks Alive: +1 point per tick

If two or more bots enter the same square on the same tick, they all die. If this square happened to be the pellet, none of those bots will be rewarded the pellet points. However, the pellet will be "consumed" and a new location will be generated for the remaining bots to eat.

If there is a tie at the end of the game among the bots, the game is a wash. A new game will be started.

2. King-of-the-hill Scoring

This challenge will combine two parts: A solo effort and a classic king-of-the-hill part.

Each bot will be given the same random seed at the start of the competition. There will also be imposed a maximum time between eating pellets to prevent bots from going around in circles to farm points.

1. Solo

Each bot will enter into a 10-game match to see how long it lasts and how well it eats by itself. The scores of each game in the match will be summed to compose its final Solo-score.

2. King-of-the-hill

All the bots will enter into a best-of-39 match. If the game ends and there is still a final living bot, the game still end at that point. That bot will be given the last man standing bonus.

The scores of each game will be summed and composed into the snakes final KOTH-score.

3. Final Scoring

All the bots will be ranked in each part separately. Ties in ranks are permitted at this stage. Then their positional rank in each part will be summed together to give their final score. The bot with the lowest combined rank wins!

In case of a tie at this level, the bot with the better KOTH rank will win. If still a tie, the bot with the better Solo rank will win.

## Sandbox Questions

My biggest concerns

1. Requires a few third-party programs to work. So that will limit the number of people who enter.
2. Requires sockets. I couldn't figure out a good way with Lua\Love2d to have bidirectional pipes with STDIN and STDOUT. So I thought sockets would be the best alternative to open the challenge to as many people as possible.
3. Too hard?
4. Haven't optimized scoring yet.

## Count the Cats code-challengeimage-processingtest-batterycounting

This is a cat:

Specifically, that is my cat. She is my only cat. And, in that image, there is only one cat: her.

These are also cats (image credit):

In that picture, there are two cats. It is relatively easy to count them, thanks to their distinct coloring.

This is a picture of 5 cats (image credit):

It's harder to differentiate the cats because of their similar coloring, but there are definitely 5.

This is a landscape (image credit):

There are no cats in this image.

## The Challenge

Given an image, output the number of cats in the image.

## Rules

• Submissions must output and terminate within 1 minute for a single image.
• Any common image format is acceptable for input, as long as no additional data (such as the number of cats present in the image) is encoded in the format.
• Submissions must be fully deterministic, and make a genuine attempt at counting the cats. Outputting a random number or a consistent but unrelated number (such as the value of the last hex digit of the SHA-256 hash of the image data) is not allowed.
• The images in the test cases will contain no animals besides cats. There may or may not be humans in the images - they are not cats, and thus should not be counted as cats.

## Scoring

The score for a single image is the square of the difference between the true number of cats in the image and the output of the submission ((actual - output)**2). The total score is the sum of all of the individual scores. The submission with the lowest score wins.

[scoring images TBD]

• I feel like this is probably a dupe of either the goat question or the rice question. I'm not sure that it being a test battery question or the precise subimage to identify really makes it much different from these other ones? – FryAmTheEggman Jun 23 '16 at 19:17
• @FryAmTheEggman I don't think it's a dupe of goats - goats wanted a boolean classification, where this one asks for a count. The rice question is closer, but there is a possibility (and perhaps a need) for different approaches, given that a) cats can overlap, b) cats come in different colors, and c) cats have much more complex shapes than rice grains (which are ellipses). – user45941 Jun 23 '16 at 19:19
• "Submissions must output and terminate within 10 seconds for a single image." I don't know about that, counting the amount of cats and only cats is a rather difficult task already, a 10-second limit seems really small. Perhaps a couple minutes? – Downgoat Jun 23 '16 at 20:03
• Also, I think there should be some specification for how the cats would appear. At least having the full cat's face showing would make this challenge more approachable. If a test-case shows the back of a cat that seems a bit too difficult for a PPCG challenge. Also: Will there be a mix of cats and other animals? Are built-ins allowed (I'm very sure there's mathematica builtin)? – Downgoat Jun 23 '16 at 20:07
• @Upgoat The time requirement can be extended. The number of cats will always be clear to a human viewer with 20/20 eyesight and adequate attention for detail. The challenge is about counting cats, not about picking out camouflaged cats, so there won't be any excessive trickery in the test images. Built-ins are allowed, but I'm on the fence about whether or not I'm going to allow them to be competitive, since Mathematica is likely the only language that would benefit from built-ins. – user45941 Jun 23 '16 at 20:12
• Showing a picture of a dog and expecting a zero output doesn't seem fair. Writing a program that distinguishes between dogs and cats seems like a difficult enough task as it is, and you have it here as sort of an afterthought. Empty images should be emptier, imo. – Liam Jun 25 '16 at 22:45
• @Liam On the other hand, if all of the test images consisted of 0-5 cats and no other animals, it would be too easy to get a perfect score. Having harder test cases means that submissions will have room for improvement, and thus there will be more competition. – user45941 Jun 27 '16 at 1:46
• Is fitting allowed? I think learning will probably be the most practical approach to this challenge. Though this does need some specification before it's ready to post imo and limits on the possible inputs as I doubt any answer will be able to conform to the wide variety of things cats can be e.g. color, position, shape, size, direction, camera position, etc. – Downgoat Jun 27 '16 at 5:15
• @Downgoat As per usual with these types of challenges, optimizing for the test cases is not allowed. However, given that a ML-oriented approach would be interesting and perform well on this challenge, I'd be willing to include a training set, separate from the scoring set. As for limits on possible inputs, I'm trying to work out a good set. – user45941 Jun 27 '16 at 5:41
• I think the part about the dog makes this a chameleon challenge -- distinguishing a cat from a dog is much harder than identifying and counting cats on an image free of distracters. – xnor Jun 27 '16 at 23:48
• @xnor On the other hand, without the distracters, it would likely be too easy to get a perfect score. – user45941 Jun 28 '16 at 2:48
• Distinguishing a cat from a dog on a picture already requires decently advanced algorithms (CNNs are the first that come to mind) which in turn require a LOT of training data to generalize decently. – Fatalize Jun 29 '16 at 9:09
• @Fatalize Would using non-mammilian animals (such as lizards and birds) be better in your opinion? – user45941 Jun 29 '16 at 9:10
• @Mego It probably would be easier because it wouldn't force people to use machine learning techniques (You could use texture comparison to distinguish feathers from scales, color detection, etc.). Counting the number of each is an added difficulty that makes it maybe too difficult as a whole. Only classifying is easier but probably a dupe of the goats challenge. Only counting might be good though. – Fatalize Jun 29 '16 at 9:14
• The problem with this scoring technique is that even if people make legit attempts at counting the cats, they will try to optimize their code for the limited test set, which will make their approaches less general on new data. One solution could be to provide a validation set (for say 2 weeks if that's the time frame in which you can post an answer) on which people can evaluate their answers, and choose the winning answer based on a test set that was not available during those 2 weeks containing new images. – Fatalize Jul 1 '16 at 13:27

# The Ifelse Tower

You are an inhabitant of the whimsical country of Forance, filled with programmers.

Life in Forance is said to be extremely repetitive, which isn't good to attract tourists. For this, authorities of Forance want to hire someone to print tons of postcards to promote their most iconic landmark: the Ifelse tower.

                   if
if
if
if
if
if
if
else
else
ifelse
else
else
ifelseif
ifelseif
elseifelse
ifelseifelse
elseifelseifelse
ifelseifelse
ifelseifelse
else    else
else      else
else        else
else          else
else            else
ifelseifelseifelseifelseif
ifelseifelseifelseifelseif
ifelseifelseifelseifelseif
ifelseifelseifelseifelseif
elseifelseif    elseifelseif
elseifelse          elseifelse
ifelseif                ifelseif
ifelse                      ifelse
ifelse                        ifelse
ifelse                          ifelse
ifelse                            ifelse


But, of course, they want to do this with the least possible cost. So, if you want this job, you have to show you can do this with very little code

## Challenge

Write a program or function that takes no input, and outputs to STDOUT the Ifelse tower.

## Rules

• Leading and traling new lines are not allowed
• Leading spaces are (of course) a must
• All lines must be at most the same lenght as the base (40 chars). This means you are free to use or not trailing spaces on each line, as long as they don't surpass the base's lenght
• Standard loopholes are not allowed

This is , so shortest answer in bytes gets the job -err wins

• I'd allow a single optional trailing linefeed. A lot of languages print full lines by default. In some it's annoying to suppress that and in some it's impossible. – Martin Ender Jul 20 '16 at 7:30
• Why enforced an output to stdout? – aloisdg Jul 20 '16 at 12:41
• This challenge proposal has been inactive for over a month. I would like to take ownership of the challenge and make it ready for posting. Please let me know within the next 14 days if you have any objections and would still like to finish and post this challenge yourself. – NonlinearFruit Jun 4 '17 at 13:05

# Interpret a Formal Grammar

Given a context-free grammar, and a string, parse the string using the formal grammar and output the matches for the non-terminals.

## Examples

First line is string, following lines are grammar, then is the main grammar to parse, last line is output.

123

n -> any of
0 1 2 3 4 5 6 7 8 9
N -> n N
n

N

N [ n [1], n [2], n [3] ]

2+2*(4/2)

o -> any of
+ - / *
n -> any of
0 1 2 3 4 5 6 7 8 9
E -> o E E'
( E ) E'
n E'
E' -> o E E'
o E'
ε

E

E [ n [2], E' [ o [+], E [ n [2], E' [ε]  ] ] ]

a b

S -> S' S
ε
S' -> a   b

S

S [ S' [a], S' [ ], S' [b] ]


This grammar is the same as regex: [a b]+

## Spec

Details:

• All recursion will be right-recursive
• Rule names will consist of A-Z a-z α β γ Γ and may have a ' at the end.
• Valid Rule names:
• A
• Γ
• AB
• αβ
• foo'
• faαβdg'
• Invalid Rule names:
• 'ab (' will be at the end)
• ab'' (two ''s)
• code golf (spaces not allowed in rule names)
• Nonterminals will be lowercase, terminals upercase
• A derivation format will be:

<rule name> -> <rule>
<rule>
<rule, etc.>


meaning the rules will be lined up (when in a monospace font), by spaces.

• Symbols/rule-names will never be repeated
• ε (epsilon) means empty. i.e. ""

## Rule definition:

• If the initial rule is "any of", the second rule will exist and will be a space separated list of symbols/rule-names (maybe more than one char). There will be no rules after this
• Else, the rule will consist of space-seperated tokens which either refer to a rule or a literal. If it is not a valid rule name, assume it is a literal which should be treated as if it is a terminal.

Summing up, for input you will be given the string to parse, the grammar, and the rule to parse.

### Output:

You may output in whichever format you like as long as it is able to convey the following information. You must somehow label the match to their respective rule names. You may optionally not label terminals.

## Challenge Rules:

• Feel free to assume the input can always be parsed by the given grammar.
• External libraries (ones that have to be imported), are not allowed
• If your language has built-in parsing tools (e.g. regex) those are allowed
• If your language has a built-in to parse a grammar (i.e. some formal grammar parser), these are allowed but your solution is non-competing and you must clearly state this in the header of your answer.

This is so shortest code in bytes wins!

I may award a bounty to any particularly ingenious solutions, so try to add an explanation!

• 1. Why the special-case Greek letters in the valid rule names? That seems to add complication for no benefit. 2. Am I correct in thinking that the only way to match a literal space character is as part of an "any of" rule? Some test cases involving literal spaces would be useful. 3. What does "Symbols will never be repeated" mean? 4. The spec for the rule definition uses the words "symbols" and "tokens". It's not clear to me whether these are synonyms, and if not then what the distinction is. 5. May we assume that there is a valid parse tree for the given input? – Peter Taylor Jun 11 '16 at 11:47
• @PeterTaylor greek letters are often used in grammars. I'll address number 2, and 4. Symbols are a name of a derivation(s). – Downgoat Aug 7 '16 at 22:22
• Trying to outsource compiler design for cheddar? Lol, jk, +1! – Rohan Jhunjhunwala Aug 7 '16 at 23:29
• I must say that I never saw any Greek letters except for episilon in the formal language and parsing courses I took, but that wasn't really my point. My point was the special-casing of three lower-case and one upper-case Greek letters. If rule names could contain any character other than - > then it would be simpler. If they could contain any Unicode alphabetic character then it would be simpler (at least for regex users). Also, 6. "Nonterminals will be lowercase, terminals upercase" Does this mean that mixed case tokens are always literals? – Peter Taylor Aug 8 '16 at 7:30

# Esolang Interpreters

Using a programming language from this version of this list, write an interpreter for the next language on the list. For example, if you choose to start with LOCK, you would write an interpreter for LOLCODE. Continue this pattern (use LOLCODE to write an LCBF iterpreter, etc)
If specs of a language are unclear and the compiler is nonexistant or closed-source, ask me and I'll decide whether or not to take it off the list.

Wining Criteria:
The longest streak of compilers wins.

Proposed Edits:
Make several defined starting points. (this would make many answers too similar, though)

Edits: changed from list of all esolangs to just turing complete ones.

• I like it, but it may be a trivial task depending on what language you choose – Rohan Jhunjhunwala Aug 24 '16 at 21:37
• I think this would be better as a similar challenge to the enterprise quality code, but where the winner is the one who does the most languages at the end at you need to go in order. If you don't think so, I'll make a separate sandbox post. – Rɪᴋᴇʀ Aug 24 '16 at 21:39
• In order to prevent edits, you can simply use the version in the url: esolangs.org/w/index.php?title=Language_list&oldid=49177 – Nathan Merrill Aug 24 '16 at 21:41
• I agree with Easterly, but I'd also make it a cycle based-system. Aka, the interpreter for "!!!Batch" must be written before the interpreter for "???" can be written. You could also have multiple starting points, one for each letter. – Nathan Merrill Aug 24 '16 at 21:45
• Actually, better idea, score them based on the number of consecutive interpreters they write. – Nathan Merrill Aug 24 '16 at 21:48
• How will you deal with cases where one language is a joke language and/or not Turing complete, and therefore cannot interpret the next language? – El'endia Starman Aug 24 '16 at 21:56
• @El'endiaStarman should I use this list instead? – Bald Bantha Aug 25 '16 at 0:09
• @Nathan Merrill I think I will do that, yes. Great suggestions. – Bald Bantha Aug 25 '16 at 0:10
• @BaldBantha: That would be better, but you may still run into problems such as languages being technically Turing complete, but entirely impractical. For instance, try multiplying two numbers in Pancake Stack. – El'endia Starman Aug 25 '16 at 0:12
• @El'endiaStarman Oh, well this challenge isn't supposed to be easy. I assume the first few answers will include 2-3 interpreters (depends on the starting points, TBH), but I think it would stall for a while. TLDR: I don't feel like classifying several hundred langueges as practical or not. – Bald Bantha Aug 25 '16 at 0:16
• The bigger issue I see is that many languages don't have completely solid specs, so it's not clear what counts as a valid interpreter of the language. – Martin Ender Aug 25 '16 at 8:53

# Sesquiprimes

Given a non-negative integer N, output the Nth sesquiprime integer.

We say that a positive integer I is sesquiprime if I + ⌊I/2⌋ is prime (where ⌊...⌋ is the floor function).

For example, 25 is a sesquiprime because 25 + ⌊25/2⌋ = 25 + 12 = 37, which is prime.

Sequence A158708 is the sequence of prime sesquiprimes.

### Inputs and outputs

• N may be 0-indexed or 1-indexed, please indicate which of the two your solution uses.

• Inputs and outputs must be in the decimal base.

• N may be taken through STDIN, as a function argument, or anything similar.

• The output may be printed to STDOUT, returned from a function, or anything similar.

### Test cases

The following test cases are 0-indexed.

N        Output

0        2
1        5
2        9
4        21
8        45
15       93
16       101
23       149
42       305
100      853
1000     11693


### Scoring

This is , so the shortest answer in bytes wins.

• I don't think the link to prime sesquiprimes adds anything other than a possibility for mistakes by people too lazy to read specs fully (like me) – Jonathan Allan Sep 4 '16 at 17:34
• @JonathanAllan True. Would adding it as a comment be better to make it less appear like part of the challenge? – Fatalize Sep 4 '16 at 17:40
• Including the link as a comment and/or prefixed by Related: would probably be clearer. – Dennis Sep 4 '16 at 18:11
• This seems close to finding primes that are 1 mod 3. – xnor Sep 5 '16 at 10:18

# Slay

This KoTH is based off of the computer game, Slay. Try it out, its way fun.

# TLDR

• You start off with a bunch of small territories: you try to merge them and capture as much land as possible.
• Each territory has its own economy: each hex gives you 1 gold per turn.
• Warriors can capture and protect territory, but cost money to maintain.
• If you run out of money, all units on that territory die

# Map

• A hexagonal map is generated using Perlin noise.
• Each hexagon is randomly assigned to a player. Players will start with a similar number of hexagons, as well as a similar number of territories (see below)
• Hexagons that touch the edge of the map (or a hole in the middle), are on the beach
• Each tile has a 1/5 chance of starting with a tree: Palm tree if on the beach, pine tree otherwise
• Hexagons may contain a warrior, house, tower, grave, or palm/pine tree

# Territory

• A block of 2 or more hexagons with the same owner is considered a territory
• All territories contain exactly 1 house.
• If a territory ever doesn't have a house, it gets one in a random location, preferring: empty hexes, trees, graves, towers, and then warriors. (in that order)
• A territory "death" occurs when it is reduced/split into a single hexagon.
• Houses turn into a pine/palm (if on the beach) tree
• Warriors die (turn into graves) at the start of their next turn
• Towers disappear
• If two territories grow so that they touch, they merge and the smaller territory's house disappears.

### Finanaces

• Each territory has its own reserve/income
• Each territory starts with 10 gold in its reserve
• Territories generate 1 income at the end of each turn for each tree-less hexagon
• If you don't have enough money to pay for your units at the end of your turn, then all of your units in that territory will die (turn into graves) at the start of your next turn.
• If a territory splits, then the larger of the two gets all of the reserve.
• If a territory combines, their reserves combine

### Defense

• Certain objects give defense to its hexagon and all adjacent friendly hexagons:
• Houses (1): cannot be built, but every territory has exactly one
• Towers (2): can be built for 15 gold
• Warriors (strength): see below

# Map objects

### Warriors

• A warrior has a strength between 1 to 4 (inclusive)
• A warrior costs 10*strength to build
• A warrior costs 2*3^(strength-1) gold each turn. This means that a 4-str warrior costs you a whopping 54 gold per turn
• A warrior can move a maximum of 4 hexes each turn. Moving through enemy lands is not allowed. Capturing enemy lands ends the warrior's turn.
• If you move/build a warrior onto a friendly warrior, they combine, and their strength is summed.
• Trying to make a warrior of strength > 4 doesn't work
• If the friendly warrior hadn't moved yet, the new unit can still move
• A warrior can capture an adjacent hexagon if its defense rating is lower than its strength

### Trees

• Trees prevent a hexagon from generating income
• Trees grow at the end of each round:
• Palm trees grow onto all unoccupied adjacent beach tiles
• Any unoccupied tile that is adjacent to two pine trees grows another pine
• Trees can be removed by moving a unit onto them
• Graves turn into a pine/palm (if on beach) tree at the end of the round

# Game flow

• Between 2 to 6 players can play on a single map. (The size of the map depends on the number of players. You can expect about 50 hexagons per player)
• Turn order is randomized, but is consistent within a single game
• Once a player owns all hexagons, they win!
• @zyabin101 still not ready yet. – Nathan Merrill Aug 31 '16 at 21:35
• @zyabin101 + others finished my post! It took me a bit to ensure I got all corner cases correct. – Nathan Merrill Sep 6 '16 at 15:41

# Flexagonal datastructures

Being programmers, watching us flex aren't very interesting. Today we change that! In this challenge you will lex and flex hexaflexagons.

For a video introduction, watch viharts video(s) on flexagons

A flexagon is a shape that you can flex to reveal faces other than the top and bottom one; we are making a hexahexaflexagon, which has 6 faces. See the image below on how to fold a hexahexaflexagon out of a strip of paper.

A shows both sides of the strip. The two white triangles are glued together. This is how you would flex it:

Below is a diagram of possible states and their relationships:

The colored circles represent the 6 triangles with the same number from the first image. Each of the circes have two colors- the bottom most represent the back face (what you would see if you where to flip your flexagon around), which you don't have to consider in this challenge.

The gray circles represent how you can flex your flexagon in any given state: there are 4 different ways to flex it, we call these Left, Right, Up and Down. You don't actually flex in these directions, the important bit is that some are opposite to each other.
If you are in the center you can use Left and Right to go to the other center ones. To get out of the center you use Up and Down. If you aren't in the center you cannot use Left or Right.

Left/Down = clockwise
Right/Up  = anti-clockwise


# Challenge

Create a function or program that take as input what should be on the 18 front faces and the 18 back faces of a flexagon, a sequence of left, right, up and down flexes, and return the 8 visible faces after the flexes.

Example computation:

flex "hexaflexaperplexia"
"flexagationdevices"
[Right, Right, Left]

Divide a strip of paper into 19 triangles:
1/2\3/1\2/3\1/2\3/1\2/3\1/2\3/1\2/3   Front
4/4\5/5\6/6\4/4\5/5\6/6\4/4\5/5\6/6   Back

Write "hexaflexaperplexia" to the front of the paper strip:
1/2\3/1\2/3\1/2\3/1\2/3\1/2\3/1\2/3

hexaflexaperplexia
123123123123123123
h  a  e  p  p  x     Face 1, Initially the front face
e  f  x  e  l  i    Face 2, Initially the back face
x  l  a  r  e  a   Face 3, Initially hidden

Write "flexagationdevices" to the back of the paperstrip:
4/4\5/5\6/6\4/4\5/5\6/6\4/4\5/5\6/6

flexagationdevices
445566445566445566
fl    at    ev       Face 4, up from 3
ex    io    ic     Face 5, up from 2
ag    nd    es   Face 6, up from 1

Flex it [Right, Right, Left]
The initial visible face is 1: "haeppx"
flexing Right ..
The current visible face is 2: "efxeli"
flexing Right ..
The current visible face is 3: "xlarea"
flexing Left ..
The current visible face is 2: "efxeli"
flexed [Right, Right, Left]!

outputting "efxeli"


Example input and expected output:

> hexaflexaperplexia flexagationdevices RRL
= efxeli

> loremipsumdolorsit hexaflexamexicania LUU
= riuort

> abcdefghijklmnopqr stuvwxyz1234567890 UL
= I can't flex that way :(

> abcdefghijklmnopqr stuvwxyz1234567890 RRRRLLUDDUUUULDD
= uv1278


# Rules

• You may take input and return output in any reasonable way
• If the input is impossible, you should indicate so in some way that is distinct from regular output
• Standard loopholes apply
• This is Codegolf. Shortest code in bytes win.
• The diagram is at best confusing. The overlapping arrows are hard to read, and the fact that they're directional is just plain wrong. Then the example computation is very cryptic. To be useful the examples need to explain what each line of text means, and they should avoid duplicating letters. It would be good to make the first example show the output with zero flexes. I made my first hexaflexagon at least 25 years ago, and I carried one in my wallet for years to play with when bored, so if I find this spec lacking imagine how it must look to people who don't know anything about them! – Peter Taylor Sep 9 '16 at 22:11
• @PeterTaylor Is this remotely better? – BlackCap Sep 9 '16 at 23:09

# Draw me a Brick Wall!

I'm drawing up a plan for my house extension - and I need a simple graphic for walls...

# The Challenge

Your task is to create a program, which takes an input of the wall's dimensions and draws a brick wall, in the style of the one below.

[__][__][__][__]
_][__][__][__][_
[__][__][__][__]
_][__][__][__][_
[__][__][__][__]
_][__][__][__][_


Please notice that the rows alternate between beginning on a full brick ([__]) and a half brick (_]), to create a more realistic, stable wall.

The input will be two integers, separated by a single comma, such as 4,3 or 2,6. You can assume both integers are positive and larger than 0.

The first integer specifies the width (in bricks) and the second specifies the height (in rows of bricks).

# Rules / Notes

• This is , so the shortest code (in bytes) wins. However, don't feel like you have to beat everyone else to post your solution - I'd love to see your code!
• Standard loopholes apply, no reading from external files.
• You may optionally take the input with brackets/braces, for example (4,3) or [4,3] as long as you specify this in your answer.
• You should take the input from STDIN and output on STDOUT - if your language does not have these, please use the nearest equivalent.

## Test Cases

Input: 1,1

[__]


Input: 2,4

[__][__]
_][__][_
[__][__]
_][__][_


Input: 5,10

[__][__][__][__][__]
_][__][__][__][__][_
[__][__][__][__][__]
_][__][__][__][__][_
[__][__][__][__][__]
_][__][__][__][__][_
[__][__][__][__][__]
_][__][__][__][__][_
[__][__][__][__][__]
_][__][__][__][__][_


# Example: Python 3, 65 bytes

This is somewhat golfed but still readable.

w,h=eval(input())
for i in range(h):print(('[__]','_][_')[i%2]*w)

• very closely related or dupe – Emigna Oct 28 '16 at 13:11
• this one is related too I think – Dada Oct 28 '16 at 13:12
• Hi, welcome to PPCG! This seems like a great first challenge. There are a few related challenges regarding brick walls, like this one (inputs as different sized bricks) or this one (is it stable). But, I think this challenge is different enough. Instead of having different sized bricks as input, this simply asks for two inputs for an NxM wall, which is imho different enough from the first challenge. – Kevin Cruijssen Oct 28 '16 at 13:12
• @Emigna I'd like to think they're different, as this one is a 'more static' string to print and doesn't require an algorithm to work out a stable wall first - however I understand that they are closely related. – FlipTack Oct 28 '16 at 13:13
• @Dada Hmm, that one might be more related than the two related ones linked by me, and more towards a dupe (despite the different ASCII used for the bricks themselves). But we'll perhaps wait on some more feedback from other users. – Kevin Cruijssen Oct 28 '16 at 13:14
• The one Dada linked is similar, but not quite a dupe. The brick structure is quite a bit more flexible in Luis' challenge, given that the input is total character width and height plus a horizontal offset, whereas here it's in number of bricks. – AdmBorkBork Oct 28 '16 at 13:21
• I'd still call the previous brick printing one a dupe. The offsetting pattern is the same, and in most of the answers it would be easy to replace constants with inputs. – xnor Oct 29 '16 at 6:11

# The smallest circles

Challenge

This is a variant of the smallest-circle problem, but instead of one circle, you get three. Given a list of coordinates, output three circles such that the following conditions are met:

1. Each input coordinate must be located inside or on the perimeter of a circle.
2. The sum of the radii of all three circles must be minimal.
3. The coordinates and radii of all three circles must be non-negative integers.

You must place all three circles. You may place overlapping circles. A circle with a radius of zero that is directly on top of an input coordinate is considered to be covering that input coordinate.

Input

A list containing between 1 and 1000 pairs of integers, inclusive. Each pair of integers represents an xy-coordinate. Use whatever input format you want to use.

For example, the input...

1,1;1,2;2,2;3,3

... can be drawn like this:

Output

A list of three integer triples. Each triple contains an x coordinate, followed by a y coordinate, followed by a radius. The triples, and the integers within each triple, must be distinguishable from one another. Otherwise, the output format is not important.

Example:

1,1,1;2,2,1;3,3,2

Given this example output, circles would be drawn at (1,1), (2,2), and (3,3). The first two circles would have a radius of 1, and the third would have a radius of 2. The sum of the radii would be 4.

Test case explained

Given the input...

1,1;1,2;2,2;3,3

... you could output...

1,2,1;3,3,0;0,0,0

... or you could output...

1/2/1
3/3/0
0/0/0

The radii sums to 1, and since it is not possible to draw three circles whose radii sum to less than 1 that encompass or touch all four points, this is the correct answer.

(maybe too)

• The text says that the list is colon-delimited, but the example is semicolon-delimited. It would help readability to mention that you can place three circles at some point before "The sum of the radii of all three circles is minimal". It's not clear whether the coordinates and radii of the circles must be integers, nor whether the radii must be non-zero. Finally, some test cases would be nice. – Peter Taylor Nov 7 '14 at 18:50
• If I didn't fully address any of the comments above please let me know. – Rainbolt Nov 7 '14 at 19:41
• If the input can contain up to 1000 points it might help to have a large test case too. – trichoplax Jan 20 '16 at 22:30
• For large numbers of input points, how will you assess whether the output is of minimal total radius? Is a proof required or is it sufficient that no other answer/person can find a counterexample? You could also have a judge program / reference implementation to define the correct total radius. – trichoplax Jan 20 '16 at 22:31
• @trichoplax Hopefully I'll have a reference implementation before I post. If I decide that I am too lazy for that, then I will assume answers are correct until someone finds a counterexample. I will come up with a larger test case. – Rainbolt Jan 20 '16 at 22:37
• Does the rigid I/O format really add anything interesting to the challenge? meta.codegolf.stackexchange.com/a/8077/8478 – Martin Ender Jan 21 '16 at 10:55
• @MartinBüttner I completely relaxed the input format, and I somewhat relaxed the output format. Thanks for the feedback. – Rainbolt Jan 21 '16 at 14:12
• @Rainbolt If I read the output section right, you're allowing any distinguishable delimiters for the output now? Then it might be clearer if one of the two example formats didn't use commas as the inner delimiter (maybe use spaces for the second example or so). – Martin Ender Jan 21 '16 at 14:15
• The rewrite states two conditions which must be met, but there's a third one hidden down in the output section: that the coordinates and radii must be integers. That should be up in the first section. – Peter Taylor Jan 19 '17 at 21:13

# Make A Rotating Emoji Globe

Your task is to make a globe out of the following characters, with the line being cleared ever 1/3 of a second:

🌍🌎🌏


You must clear the line your emoji globe on it and print the next one every approximate 1/3 of a second.
Output may be to the terminal or elsewhere.
The program must also continue until interrupted on purpose.
Also, your code may not contain the emoji globes themselves, but it may contain Unicode escapes.

This is , so standard loopholes & rules apply.
May the best coder win...

• Simple, fairly identical to this in that you simply display a cycle of things, Most answers from that will fairly easily work copied over. – ATaco Feb 7 '17 at 2:47
• @ATaco How could I make it more challenging? – ckjbgames Feb 7 '17 at 2:50
• @ATaco I think it's sufficiently distinct--it requires clearing the line (an option in the other challenge), display unicode characters, and only displaying one character at a time. – Conor O'Brien Feb 7 '17 at 3:24
• @ConorO'Brien I still feel I could distinguish my challenge a bit more, though... – ckjbgames Feb 7 '17 at 17:48
• Define clear the line? Does it have to clear the line, or does the whole terminal suffice? – Rɪᴋᴇʀ Feb 7 '17 at 18:13
• @EasterlyIrk Clearing the screen can be done in any way, as long as the globe appears to rotate onscreen. – ckjbgames Feb 7 '17 at 21:40
• It's even more similar to codegolf.stackexchange.com/questions/101289/loading-forever. Printing a single character that cycles – 12Me21 Feb 7 '17 at 22:26
• @12Me21 How can I make it different, then? – ckjbgames Feb 7 '17 at 22:35
• Maybe you could require them to draw an actual rotating globe, given a map image. (It's a lot more complicated though) – 12Me21 Feb 7 '17 at 22:37
• @12Me21 I just had the idea to add a moon rotating around the earth. Help me think of how to implement it. – ckjbgames Feb 7 '17 at 22:59
• You could make it use the different moon phase emoji to display the proper phases or something – 12Me21 Feb 7 '17 at 23:05
• @12Me21, an actual rotating globe is potentially a dupe of codegolf.stackexchange.com/q/24326/194 - certainly some of the answers could be copied across. – Peter Taylor Feb 9 '17 at 9:02
• Take as input the "spin speed" (ms delay), althought that's fairly trivial to handle. – Carcigenicate Feb 10 '17 at 22:13
• @Carcigenicate I will do that. – ckjbgames Feb 12 '17 at 21:54

# Tron Game

Write a Tron bot!

The aim of the game is to make as many moves on a grid as possible without moving onto a space that has already been occupied in the current game. If your bot is unable to make such a move, it loses the round. The board does not wrap so bots can not go off the side of the arena.

## Game IO:

Your bot will be written in python and will create a class that inherits from BotSkeleton. An example test bot is shown below.

from bot_skeleton import BotSkeleton
from typing_hints import PositionDict, Position
from board import Board
from typing import List

import random

class Test(BotSkeleton):
def make_move(self, board: Board, positions: PositionDict) -> Position:
self.board = board
self.position = positions[self.bot_id]
valid_moves = self.get_valid_moves()
try:
return random.choice(valid_moves)
except IndexError:
return None

def get_valid_moves(self) -> List[Position]:
moves = filter(self.board.position_valid, ((self.position[0]+1, self.position[1]),
(self.position[0]-1, self.position[1]),
(self.position[0], self.position[1]+1),
(self.position[0], self.position[1]-1)))
return list(moves)


(Type hints are not required but illustrated here to help understanding)

• position is a 2-long tuple containing 2 integers.
• positions is a Dict[bot_id, position]
• board can be indexed with a position.
• get_random_empty_pos() -> position - returns a empty position at random in the board
• position_valid(position) -> bool - returns if this move is valid (but not next to the position given)
• copy() -> List[List[int] - returns a 2d list that can be modifiable of the current board state
• EMPTY - the id for an empty space
• The value you return must be a position, and must also have a distance of 1 from this, not including diagonals.

Built in attributes for BotSkeleton:

• log - contains a file object that you may write to
• no_bots - the number of bots the game began with
• bot_id - you're bot's id number.

Methods in Board:

• get_random_empty_pos() -> Position - Returns a position at random that is empty
• position_valid(pos: Position) -> bool - returns if a position is inside the board and is currently empty
• copy() -> Board - return a copy of the board that is writable

## Tournament structure

• Every bot will get pitted against every other bot in a giant arena
• That is to say every single bot will be in every battle
• The size of the arena will be (30, 30). This may be increased depending on number of bots entered.

### General rules that I can't find better places for

• Your bot may NOT use any file storage except for write-only access to the log file provided
• Your bot must be written in Python 3. Sorry java people
• You may enter as many bots as you want
• Your bot must not attempt to subvert the game state

### I reserve the right to disqualify any bot from the competition

(but shall only do so after telling you I will do so and you not making any changes required)

• Results here

## Sandbox notes:

• Should there be a minimum starting distance between players?
• What happens if two bots go on the same position at the same time? – Katenkyo Mar 23 '16 at 11:10
• Is the goal really to survive as many moves as possible, and not to survive longer than the other guy? – feersum Dec 7 '16 at 14:03
• probably change "sorry" to "sorry not sorry" – Destructible Lemon Feb 11 '17 at 12:20

# Part II: Triangular Chebyshev Distance

The Chebyshev distance on a regular grid is the number of orthogonal or diagonal steps one needs to take to reach one cell from another. That is, we can move either through the edge of a cell, or through a corner, to a neighbouring cell.

We can define a similar distance on other grids, for example the triangular grid. We can address the individual cells in the grid with the following indexing scheme, where each cell contains an x,y pair:

    ____________________________________...
/\      /\      /\      /\      /\
/  \ 1,0/  \ 3,0/  \ 5,0/  \ 7,0/  \
/ 0,0\  / 2,0\  / 4,0\  / 6,0\  / 8,0\
/______\/______\/______\/______\/______\...
\      /\      /\      /\      /\      /
\ 0,1/  \ 2,1/  \ 4,1/  \ 6,1/  \ 8,1/
\  / 1,1\  / 3,1\  / 5,1\  / 7,1\  /
\/______\/______\/______\/______\/___...
/\      /\      /\      /\      /\
/  \ 1,2/  \ 3,2/  \ 5,2/  \ 7,2/  \
/ 0,2\  / 2,2\  / 4,2\  / 6,2\  / 8,2\
/______\/______\/______\/______\/______\...
\      /\      /\      /\      /\      /
\ 0,3/  \ 2,3/  \ 4,3/  \ 6,3/  \ 8,3/
\  / 1,3\  / 3,3\  / 5,3\  / 7,3\  /
\/______\/______\/______\/______\/___...
/\      /\      /\      /\      /\
.  .    .  .    .  .    .  .    .  .
.    .  .    .  .    .  .    .  .    .


Now the Chebyshev distance on this grid is again the minimal number of steps across edges or corners to get from one cell to another. So you can move from 3,1 to any of its 12 neighbours:

2,1 4,1 3,2 (through edges)

3,0 1,2 5,2 (the opposite triangle through corners)

2,0 4,0 1,1
5,1 2,2 4,2 (the other triangles through corners)

For instance, the distance from 2,1 to 7,2 is 3. The shortest path is generally not unique, but one way to make the distance in 3 steps is:

2,1 --> 4,1 --> 5,1 --> 7,2


## The Challenge

Given two coordinate pairs x1,y1 and x2,y2 from the above addressing scheme, return the Chebyshev distance between them.

You may assume that all four inputs are non-negative integers, each less than 128. You may take them in any order and arbitrarily grouped (four separate arguments, a list of four integers, two pairs of integers, a 2x2 matrix, ...).

You may write a program or a function and use any of the standard methods of receiving input and providing output.

You may use any programming language, but note that these loopholes are forbidden by default.

This is , so the shortest valid answer – measured in bytes – wins.

## Test Cases

Each test case is given as x1,y1 x2,y2 => result.

1,2 1,2 => 0
0,1 1,1 => 1
1,0 1,1 => 1
2,1 7,2 => 3


Will add more test cases when I have a reference implementation.

• @trichoplax Yes, thank you. With the slow response to the Manhattan variant, I do wonder whether this one will be a bit too tricky, but we'll see. :) – Martin Ender Apr 4 '17 at 21:28
• "I do wonder whether this one will be a bit too tricky, but we'll see. :)" I've found a solution for this one, but not for the other one yet. ;) – Kevin Cruijssen Apr 5 '17 at 12:01
• @KevinCruijssen Oh, would you mind sharing it? :) – Martin Ender Apr 5 '17 at 12:06
• I always make my answers in Java 7 btw, so I'll still be beaten by golfing answers. But this is what I came up with (I've also added an explanation of how I came up with the solution in the TIO footer): Try it here. – Kevin Cruijssen Apr 5 '17 at 12:23
• Hmm, I just took another look at your part 1 challenge and realized my solution above for part 2 is incorrect.. :( Based on your current test cases I falsely assumed x1,y1 is always smaller than x2,y2. So my code fails for a test case like 4,1 1,3. Back to the drawing board.. Also, as to why I think this challenge is easier than part 1: In part 1 you had to determine whether the triangle was facing upwards (available: left; right; below) or facing downwards (available: left; right; above). With this challenge all 12 surrounding triangles - regardless of orientation - are accessible. – Kevin Cruijssen Apr 7 '17 at 8:22
• @KevinCruijssen but the exact coordinates/orientations of those 12 neighbours also change, right? – Martin Ender Apr 7 '17 at 8:24
• Yeah, was about to edit my comment again when I realized that.. If you have more test cases I'll take another look at this part 2. I'll start with part 1 for now. (PS: Have a nice weekend - apparently I can use it.. >.>) – Kevin Cruijssen Apr 7 '17 at 8:25
• Me again, more than one year later. I've currently set a bounty for your Part 1 challenge to give it more attention, which you may or may not have noticed based on the new answers given. If you have time, could you add more test cases for this one? – Kevin Cruijssen Jun 29 '18 at 8:40
• @KevinCruijssen I'm not sure how soon I'll get around to that, because I'd want to write a reference implementation for that. If you want it post it soon, feel free to add them yourself (and optionally post the challenge yourself if you like). – Martin Ender Jun 29 '18 at 16:26
• Oh no, I'll patiently wait. I'm going on vacation soon anyway, so I won't have time to answer during that time. I just made that comment above as a reminder so it can hopefully be posted in the not to distant future. :) – Kevin Cruijssen Jun 29 '18 at 16:42

### Table parser, code golf

Input

|===========|=============|==============|
|Left align |  Right align| Center align |
|===========|=============|==============|
|This       |         This|     This     |
|-----------|-------------|--------------|
|                column                  |
|-----------|-------------|--------------|
|will       |                            |
|-----------|          will be           |
|be         |                            |
|-----------|-------------|--------------|
|left       |        right|    center    |
|-----------|-------------|--------------|
|aligned    |      aligned|   aligned    |
|-----------|-------------|--------------|
|and can be |    vertical-|              |
|multilined | align middle|  as default but a bit long line |
|with <br>  |             |              |
|-----------|-------------|--------------|

Output should be valid HTML. And I am thinking of following requirement specs.

• alignments (left, right, middle)
• border thickness (normal -, |, bold, =,||)
• with table headers or without
• rowspans, colspans
• multiline & vertical-align is always middle

What do you think?

• I guess figuring out cells and row/colspans is enough work, so handling bold and italic could be omitted, maybe. – Joey May 9 '11 at 12:15
• Also, should this be a code golf or a challenge? – Joey May 9 '11 at 12:18
• code-golf @joey. and I am gonna leave bold and italic out. I was not sure it was hard enough :D – YOU May 9 '11 at 13:22
• Can cells contain more than a line of text? I.e. do long contents wrap or do they extend the cell? – Joey May 9 '11 at 13:35
• @Joey, yeah, a bit more complicated now, multiline involve vertical-align, so I set that as middle as default, what do you think? – YOU May 9 '11 at 13:49
• Yikes :D. Well, I was just pondering a few ways of figuring out the layout and determining rowspans would be much easier if all rows are the same height ;). Should be ok, but bear in mind that it makes judging correct vertical align difficult. Given the current last row the valigns could be either one of mmm, ttm, tmm, btm, bmm. No show-stopper but something to keep in mind for test cases and scripts. – Joey May 9 '11 at 13:53
• @Joey, yeah, to judge top, middle, and button, we need a blank row between every table row, just like a space in right, right, and center, so I guess I need to make vertical-align as middle as default. – YOU May 9 '11 at 14:06
• So vertical align will not vary and always be middle, if I understand you correctly? – Joey May 9 '11 at 14:07
• @Joey, yeah .. and for multiline items you just need to put <br> between and can be, multilined, and too, if those are supposed to be same line, input will be |and can be multilined too | ....... | ..... | . – YOU May 9 '11 at 14:10
• I think your multi-column cells are ambiguous: the last row shows that text can extend beyond the ASCII art column width, so we cannot use the horizontal alignment of |s to judge colspans. Therefore, the 4th and 5th rows could span 1 and 2 columns (as visually, but unreliably indicated) or 2 and 1 columns. Example – Adám Jun 5 '17 at 7:20
• @Adám, thanks for taking a look. Yeah, might be that's the reason there is not much interest on this. – YOU Jun 5 '17 at 10:33
• @YOU Also, this is a very complex challenge, pretty much implementing a large subset of the Wiki markup for tables. Maybe you should narrow the scope by removing all formatting; alignment, borders, headers (these are also ambiguous), and just focusing on converting the -| style table into HTML. Maybe even remove the row and column spans? – Adám Jun 5 '17 at 10:42
• I don't remember why I put all those things in, may be similar challenge was there already, for simple tables, but I don't know. I need to look up more. – YOU Jun 5 '17 at 14:11
• @Adám, removed rowspan, colspan, multiline and vertical align. Not sure it could be duplicate entry now. – YOU Jun 5 '17 at 14:17
• @programmer5000, became duped, because of you guys suggestion. I rollbacked. – YOU Jun 9 '17 at 15:37

# Line up for golf!

• The comments in the test cases reduce their usefulness as test cases. Moreover, the first one contradicts the "full specification", and the second one adds to it. The spec should contain everything needed to justify the correctness of the test cases. You also need to specify desired behaviour when there is no solution, and to include a test case for that scenario. – Peter Taylor Mar 7 '14 at 14:04
• How are conditionals to be interpreted when mixed in a single full condition? Alice is 1st or 1st to last and in front Bob or 1 space behind Bob – John Dvorak Mar 7 '14 at 14:12
• This seems like a good challenge, but Peter Taylor and Jan Dvorak's concerns should be addressed. – user10766 Mar 8 '14 at 18:42
• @PeterTaylor Edited, but how does the first one contradict? – Doorknob Mar 10 '14 at 2:32
• @JanDvorak Edited to clarify. – Doorknob Mar 10 '14 at 2:32
• Another concern: What if there is no solution? What if there is more than one? – John Dvorak Mar 10 '14 at 6:04
• Please delete this now that it is posted. – programmer5000 Aug 1 '17 at 16:07

This message is open for anyone to adopt and post to main. For more details, see the chat room or meta post.

# Ping an IP address continually and report the dropped to returned ratio

Create a console program that pings an IP address at most once per second and reports the ratio of dropped to returned packets to the screen in real time.

The IP address will be provided on the command line in standard IPv4 notation. (eg. 192.168.0.1)

The 'ping' method should be ICMP echo (See here for a summary of ICMP packet structure) with a packet size of at least 32 bytes.

Your program must be "standalone" and cannot rely on external programs, libraries, or resources.

This is so let the shortest answer win

• ping isn't enough? – TheDoctor Apr 7 '14 at 19:31
• ping works great, except you have to tell it when to stop to get the final tally – David Wilkins Apr 7 '14 at 19:32
• I think you're assuming that everyone will interpret this as sending the same ICMP control packet that ping sends, but it would be an improvement to the question both to make this explicit and to link to some documentation about ICMP. – Peter Taylor Apr 7 '14 at 22:46
• Actually I left it ambiguous. Any IP request that elicits a response can be considered a ping. – David Wilkins Apr 8 '14 at 1:00
• Alright, lets make it easier and say ICMP specifically... – David Wilkins Apr 8 '14 at 12:16
• Well this doesn't have enough upvotes...I'll leave it in the sandbox, but likely it will not be posted – David Wilkins Apr 9 '14 at 12:17
• 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.) Due to community guidelines, if you don't respond to this comment in 7 days I have permission to adopt this. – programmer5000 Jun 9 '17 at 16:34
• @programmer5000 be my guest :) – David Wilkins Jun 9 '17 at 16:40

This is a proposal adopted by programmer5000. Any feedback before I post it?

# Seven-segment usage

I have an old digital clock and I am concerned the individual segments of the digits might run out of magical binary energy or whatever powers them. To know which of the segments on the clock will fail first I want to know what is the percentage of time each segment is lit.

The challenge is to compute the percentage of time any segment on a digital clock is lit.

## Input

The input will be in the form X.L, where:

• X is a number from 1 to 4. 1 is the left-most number of the clock, 4 the right-most
• L is a letter from a to g or a number from 1 to 7
• the separator can be changed to fit your needs (no separator is an option)

## Output

The output, is a percentage, given with at least 2 figures after the decimal point. It can be rounded or truncated to the closest value if you want to keep a limited number of digits.

Valid outputs: 0.74, 32.47, 7.5 (for 7.50)

The clock is in 24 hours format (so 22:45 is a valid time).

We consider the clock started working at 0:00 so the challenge is effectively working out what percentage of a complete day a single segment is lit.

The first number is not lit when it is 0.

Lit segments for each number:

• 1: b c
• 2: a b d e g
• 3: a b c d g
• 4: b c f g
• 5: a c d f g
• 6: a c d e f g
• 7: a b c
• 8: a b c d e f g
• 9: a b c d f g
• 0: a b c d e f

## Examples

• 1.b => 58.33
• 3.e => 33.33
• 2.d => 70.83
• 4.d => 70.00

Full list of outputs here

## Winner

Code golf, most probably, though I am not sure yet this is the best format (I am not too interested in the input parsing and the output formatting, they might be an obstacle to golfing?)

• AIUI there are 28 valid inputs, so you could provide a full list of test cases as a pastebin. I would remove "No hard coding of results": if hard-coding the 28 cases is shorter than the calculation, then IMO that's a flaw which makes the question not worth bothering with at all rather than something which can be worked around; and the issue of whether or not an answer "hard-codes the results" is likely to be grey rather than black or white. – Peter Taylor Mar 3 '16 at 10:54
• List of results added, I'll need to double check them. Hard coding removed, yes I don't see how "cheating" would be an issue. Any hard-coding would have to be quite constructive to be efficient. – drolex Mar 3 '16 at 11:29
• I am removing limitations on the output as well, I don't think it brings anything to the challenge. I have started to golf a solution in python, I think there are a few interesting possibilities to optimise the use of strings describing segments used for each digit. – drolex Mar 3 '16 at 15:56
• Can I post this abandoned proposal? – programmer5000 Jun 9 '17 at 13:00
• @programmer5000 certainly, just try to make it better :) – drolex Jun 9 '17 at 13:05

# What is your Operating System?

I can't believe we haven't had this one before

To avoid any doubts about what constitutes a separate OS, you must return an index into your chosen subset (containing minimum two) of the following OS families. You may order your set as you like, so include your ordered set, and state if you use zero or one based indexing. You may also bunch together families you cannot distinguish between.

Windows, Minix, Linux, macOS, BSD, HP-UX, AIX, Solaris, Unix, Z/OS, OS/2, QNX

Your score is your byte count divided by the square of the number of indices your code can return – given that it is run on the appropriate OSs, of course.

You do not have to account for virtual machines, emulation layers etc., e.g. WSL and Wine.

### Examples

Your code can detect Windows, macOS, AIX, and Linux. It returns 0 for Windows, 1 for macOS, 2 for AIX, and 3 for Linux. Your score is a sixteenths of your byte count.

Your code can distinguish between Z/OS, OS/2, and UNIX/Linux/AIX. It returns 1 for Z/OS, 2 for OS/2, and 3 for any UNIX-like OS. Your score is a ninth of your byte count.

• 2 is definitely better than 1. After that I think it may just be your preference for the kinds of answers you want. I think 3 will promote more answers that reach, while 2 will promote more 2 answers. However, if you really want to reach maybe make the denominator grow as a square? These scoring mechanisms are unfortunately very important to these kinds of challenges as well as very hard to figure out beforehand. I'd ask around and see what other people think! – FryAmTheEggman Jun 15 '17 at 0:37
• @FryAmTheEggman Thanks. – Adám Jun 15 '17 at 0:39
• Are not macOS, BSD, and Linux Unix? Is OSX considered the same as macOS? – Wheat Wizard Jun 21 '17 at 14:53
• The I/O requirements are rather strict, could you not just print/return the name of the OS? – musicman523 Jun 21 '17 at 14:56
• @WheatWizard Yes, but you may pick whichever many you want from that list, so you can bunch all Unixes together or keep them separate, or you can detect specific flavors while also detecting vanilla Unix. – Adám Jun 21 '17 at 15:02
• @musicman523 I'd rather have comparable output from all solutions. – Adám Jun 21 '17 at 15:03
• It seems like people with access to proprietary OSs will have an advantage in this problem. For example, to ensure my code runs on Windows I have to buy windows, because I don't own it. I happen to own a copy of OSX, but other users might not given me an advantage. I feel like this is problematic. (also is OSX considered the same macOS?) – Wheat Wizard Jun 21 '17 at 15:09
• @WheatWizard You're right, but that will be problematic in detection of OSs no matter what the challenge is. And yes, good luck testing your solution on Z/OS… – Adám Jun 21 '17 at 15:34
• It's not just that. If I claim to detect Windows, which versions of Windows do I have to test it on? And what can I assume about e.g. the C header files that are available? – Peter Taylor Jun 21 '17 at 15:35
• @WheatWizard Oh, and yes, OSX and macOS are the same (I don't expect anyone to submit an answer that will run on MacOS 9-) – Adám Jun 21 '17 at 15:35
• @PeterTaylor Good point. Any ideas how to fix this or is it doomed? – Adám Jun 21 '17 at 15:36
• I suspect that the difficulties around specification and testing might explain why this hasn't been asked already. – Peter Taylor Jun 21 '17 at 15:44
• Why numbers only? Why not just outputs? – CalculatorFeline Jun 21 '17 at 16:00
• Is the set of OSes listed there exhaustive? (I've done some programming on SunOS in the past, for example, although I don't have access to it right now.) Also, "Unix" seems a bit strange to have in the list; many of the listed OSes (e.g. BSD and Solaris) are flavours of Unix. It's also worth being aware of cases like WSL and Wine; which OS should they count as? – user62131 Jun 22 '17 at 10:28
• @ais523 "Unix " allows submissions to bunch together various flavors as one, and also allows differentiating the other Unixy OSs from vanilla Unix. I'll add a note about virtual machines etc. – Adám Jun 22 '17 at 14:54

# A Game of Knights

In this King of the Hill, you control 10 Knights. You need to surround your enemy before they surround you.

Each Knight has 3 possible actions:

• Dash: Move 3 squares in a cardinal direction. If there is a knight in your path, move as far as you can.
• Leap: Move 2 squares in a cardinal direction. If there is a knight on your destination square, don't move at all.
• Push: Move 1 square in a cardinal direction. If there is a knight on your destination square, and no knight or wall behind him, you both move 1 square.

Each round will have a Planning Phase and then an Action Phase.

Planning:

During the planning phase, players will alternate creating a plan until both players have created 10 plans.

• A plan consists of either an action type or a cardinal direction (not both).
• A plan also includes the knight that will perform the action
• All plans are revealed to both players

Action:

• Actions occur in the same order that they were planned.
• If you planned an action type, you will be able to choose the direction. If you planned a cardinal direction, you will be able to chose the action type you want.

After the action phase, if any knights are on the same location they started at (at the start of the round) are captured and removed from the game. You win by capturing all other knights.

Other info:

• Cardinal means North, East, South, or West
• The board is a 10x10 board. Your knights start as a line at the bottom of the board.
• Walls block movement and cannot be pushed.
• You don't have to plan an action for every knight, and a knight can take multiple actions.
• There are a maximum of 1000 rounds. After those 1000 rounds, the winner is the player with the most knights. (A tie is allowed).
• The starting player for a game is randomized, and that player starts every round.

You have won the game when you opponent cannot make any mobility actions.

• Man, now I want to play this in person. – DLosc Feb 18 '17 at 21:17
• Isn't it possible to form your knights into a solid 2×5 rectangle (thus immune to pushing), away from the starting squares, before the enemy can move and push it? That would guarantee you couldn't lose. Also you should clarify whether you can plan two actions for the same knight, and if you can, whether it gets to take both or only one. – user62131 Feb 18 '17 at 23:14
• @ais523 movement is not simultaneous. You start as a 1x10 line. A knight could take 10 moves on a round – Nathan Merrill Feb 18 '17 at 23:52
• To be clear, as long as you have 10 knights, you need to move each of them every round or lose the ones you didn't move, assuming you don't push. Correct? – isaacg Jun 23 '17 at 21:30
• Does the same player go first in each round, or does that alternate? – Peter Taylor Jun 23 '17 at 21:31
• @isaacg correct. – Nathan Merrill Jun 23 '17 at 23:51
• @PeterTaylor I've debated about this, and I think the same player will go first in each round. The player that goes first will be randomized each game, but it will be consistent round to round. Otherwise, you end up with a player being able to move twice in a row. – Nathan Merrill Jun 23 '17 at 23:52

# One OEIS after another

• This sounds fun! – Luis Mendo Jul 19 '17 at 22:32
• Awesome frickin' idea. You might wanna add what to do when one answer reaches 289,585 bytes ('cause obscure esolangs). ;) – totallyhuman Jul 19 '17 at 22:41
• @totallyhuman I would've thought that that score is about right for Java, so I'll address that – caird coinheringaahing Jul 19 '17 at 22:59
• A possible problem is that many languages have "add 1" and "subtract 1" or similar functions that are inverses of each other. So you could add any even amount of bytes. For example, sequence A005843 (the even integers) in CJam can be ri2* or ri2*()()()()()()()() – Luis Mendo Jul 19 '17 at 23:07
• Ah, no, the rule is that removing any subset of the characters must give wrong output. That rule is enough to invalidate the above – Luis Mendo Jul 19 '17 at 23:08
• I think the rule about the program having to be pristine is bad for this challenge. It makes writing answers incredibly difficult in most languages. Why do you care if people change the length of their post? All they can do is control which sequence appears next. – FryAmTheEggman Jul 19 '17 at 23:19
• You might want to bold or otherwise emphasize unused language, as I missed it the first couple times I read through (or just remove that restriction, because it would be more fun if we had to go through all sequences instead of all languages ;) ). Also, what to do about very short sequences, such as the busy beaver sequence? – Stephen Jul 21 '17 at 13:01

# Invisible Ink, Easy code-golf

In the physical world, invisible ink usually becomes invisible when it dries, and is then is readable if it is exposed to heat or chemicals of some kind. The invisible ink in this challenge will be readable when exposed to highlighting.

Create a full program or function that takes in text from the console (using a prompt) and outputs it the console so it cannot be seen unless highlighted.

## Notes:

• Assume that the console is a solid color (black, white, green, etc.).

# Swap the frogs!

Given 2 integers N >= 1, representing left-side frogs, and M >= 1, representing right-side frogs, return all the steps required so that the frogs change sides with the minimum number of steps. The frogs start with one empty spot between the two sides. A frog can jump to the empty space if there is at most 1 frog from either side between the frog and the empty space. A frog can jump either forwards or backwards.

An example, with N = 3 and M = 2:

LLL.RR
LL.LRR
LLRL.R
LLRLR.
LLR.RL
L.RLRL
.LRLRL
RL.LRL
RLRL.L
RLR.LL
R.RLLL
RR.LLL


The corresponding output would be (1-indexed):

[3, 5, 6, 4, 2, 1, 3, 5, 4, 2, 3]


Each one is the index of the column that the frog that must jump is before jumping.

# Rules

• You may perform I/O in any reasonable format.
• Maybe start with a small example, because now the main output specification is tucked under a huge block of text, which will be TL;DR for many people. – Sanchises Aug 8 '17 at 10:52
• 1. The questions in the section headed "Sandbox" make no sense because their context has been deleted. Are they still relevant? 2. "What you have to print" should presumably be "What you have to output". 3. "A frog can jump either forwards or backwards" so there should be at least one test case where all optimal paths only involve jumping forwards and at least one where all optimal paths involve jumping backwards. – Peter Taylor Aug 8 '17 at 14:55
• Maybe a testcase where no steps are necessary, too. – Sanchises Aug 8 '17 at 15:13
• @PeterTaylor Please, don't be too meta :-) :p – Erik the Outgolfer Aug 8 '17 at 16:46

# Learning your strengths and weaknesses king-of-the-hill

• Fighters have a unique, random Strength (between 1 and 1000)
• When two fighters fight, the stronger one wins.

## Gameplay:

1. We start by randomly ordering all 1000 fighters.

2. Each fighter fights his neighbor (The even fighters fight the fighter 1 above)

3. The fighter is given two pieces of information: His opponent's last guess, and who won the fight. The fighter then guesses his strength.

4. We perform a stable sort based on the guessed strength, and go back to step 2

5. After 10 guesses, the fighter's score is (RealStrength - GuessedStrength)^2. Lower is better.

# Other details:

• There will be duplicate bots in a single game.

• A stable sort is a sort that (effectively) uses the past ordering as a tiebreaker. In essence, if players [A,B,C,D] guessed [10,5,10,5] then the new order would be [B,D,A,C]

• Bots aren't allowed to share information between each other, but are allowed to persist information within a single game.

• I will run a large number of games. The exact number will be dependent on how much variation there is. Your final score will be all of your scores summed up.

• I like this a lot. Sounds like a very interesting challenge. A couple thoughts though. 1) What's the point of squaring your score? If there was some kind of polynomial scoring I could see that, but it doesn't really have any purpose at the moment. 2) personally, I think it should be more than 10 rounds. – James Jan 29 '18 at 17:17
• @DJMcMayhem I think 10 rounds is enough for good bots to get a reasonable score without providing so much information that many will get a perfect score. I do think the process should be repeated though. Maybe a terminology change: 10 guesses per round, each round scored as indicated, average of X rounds is the final score. Also, the squaring is a way of getting absolute value (result is always positive even if guess > real) and if averaging multiple results it weights wildly incorrect guesses to increase the score by a lot. – Kamil Drakari Jan 29 '18 at 17:45
• @DJMcMayhem Squaring means that being 50 off is far worse than being 25 off. I picked 10 rounds because log2(1000) is 9.97. This requires bots to be efficient with their time. If I make it much higher, then its going to be hard for me to differentiate the top bots. – Nathan Merrill Jan 29 '18 at 18:24
• @KamilDrakari Updated, thanks. – Nathan Merrill Jan 29 '18 at 18:30
• In step 3, each fighter is provided "His opponent's last guess". What will be provided during the first round? – Kamil Drakari Jan 29 '18 at 19:21
• That'll be part of the API spec. Something like -1. – Nathan Merrill Jan 29 '18 at 19:31
• This will probably be my last suggestion (for now): a link and/or description for "stable sort" will probably be helpful; I certainly needed to look it up, and is quite useful for informing strategies, as well as answering a question I otherwise had about handling ties. – Kamil Drakari Jan 29 '18 at 22:00

## Can the robotic arm reach itself?

( ͡° ͜ʖ ͡°) title is kinda sketch at the moment

A robotic arm is made up of a set of line segments, each with a positive integer length. Each joint on the robot has two possible positions: straight or 90 degrees clockwise.

Here is a robotic arm with 4 line segments of sizes 4, 2, 3, 2

+---+-+--+-+


Here is the same robot arm with one joint bent

+---+-+
|
|
+
|
+


(vertical scale is kinda messed up)

Right now, the robotic arm isn't reaching itself. By bending all of the segments, however, the arm can reach itself.

+X--+
|  |
+--+


So, a robotic arm of size [4,2,3,2] can reach itself.

Here is a robotic arm of size [3,1,4,3] that can't reach itself:

+--++---+--+

+
|
|+--+
+---+


Whereas a robotic arm of size [1,1,2,2,3] can reach itself.

++-+-+--+

+
X++
| |
+-+


A robotic arm of size [2,2,3,5,3,4] can also reach itself

a-b-c--d----e--f---g

e--f
|  |
|  |
|a-b
|  g
d--c


## Challenge

Given list of numbers, such as [1,2,3,4,5], output a truthy value of the robotic arm can reach itself and a falsey value if it cannot.

• s/touch/intersect/g? – El'endia Starman Feb 17 '16 at 20:27
• We've had some related challenges I think. At least codegolf.stackexchange.com/q/45059/8478 – Martin Ender Feb 17 '16 at 21:01
• codegolf.stackexchange.com/q/49713/8478 – Martin Ender Feb 17 '16 at 21:03
• The scenario reminds me of stretchy snakes kissing. Except, these snakes are unusually rigid ... you know what, never mind. – xnor Feb 17 '16 at 21:45
• The first few examples would be clearer if either you also used letters to distinguish the joints or if you at least marked one end of the chain in both the straight and the folded representation. – Martin Ender Feb 18 '16 at 7:55
• You could probably also use more than one example where self-intersection only happens when not all joints are bent like the [1,1,2,2,3] example. If that's possible it would be good to have one where you need to bend joints on both sides of a straight joint to make the self-intersection happen, but I don't know if that can happen. – Martin Ender Feb 18 '16 at 12:23
• @El'endiaStarman s/touch/reach/g – mbomb007 Apr 7 '16 at 15:13
• Is 4,2,3,3 truthy or falsy? – Zgarb Feb 7 '18 at 8:12
• Can the robotic arm go through itself? The [2,2,3,5,3,4] case seems to indicate so. – stanri Feb 7 '18 at 10:50