Sandbox for Proposed Challenges

Question

What is the Sandbox?

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

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Answer 1

Insert Random Squares Here

graphical-outputrandomcode-golf

---

^{Related challenges.}

< Insert sales pitch here >

The Challenge

Given a width and a height, output an image filled with random squares.

Input

Your program/function is given a width and a height in pixels.

E.g.:

yourProgram <width> <height>

Output

You must display the result on the screen, or output an image file in any acceptable format.

Rules

• The number of squares to be generated is a random natural number between sqrt(w * h) / 2 and sqrt(w * h) * 2 (inclusive).
• Each square's color will be randomly generated for each with R, G, B ranging from 0-255 and with alpha values ranging from 1-255.
• Each square's width/height will be a random value between 1 and min(w, h) (inclusive)
• Each square must be placed randomly. Part of the square may be outside the output image, as long as at least one pixel of the square is visible.
  • Placement at sub-pixel coordinates (e.g. x=0.239420, y=2.8298329) is allowed but not required.
• Each possible output must be equally likely to occur.
• The output must have a white or transparent background.

Example

Input and randomly generated parameters

Width: 10
Height: 20

Maximum square height: 10

Minimum number of squares: 8 Math.sqrt(10*20)/2 = 7.0710678118654755
Maximum number of squares: 28 Math.sqrt(10*20)*2 = 28.284271247461902

Number of squares  in this example: 8

Output

Scaled 2000%:

Output with the parts of the squares that are off-screen

(Scaled 2000%.) The gray part is the part that is displayed on the screen.

Answer 2

A Fine-Grained Mesh

code-golf

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

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

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

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

Standard loopholes disallowed.

Answer 3

Flit - a simple board game for bots

king-of-the-hill

---

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

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

---

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

Overview

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

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

Neutral pieces

There are initially zero neutral pieces.

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

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

Moving

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

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

Communication

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

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

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

Specification

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

Players

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

Board

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

Initial state

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

Addition of neutral pieces

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

Bot STDIN

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

Update:

x y c

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

Move request:

M

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

Bot STDOUT

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

x0 y0 x1 y1

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

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

Time limit

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

Winning criterion

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

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

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

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

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

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

Answer 4

Musical Washing Machine

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

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

The Challenge

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

I/O coming soon to a washing machine near you

Answer 5

Make a Sierpinski triangle

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

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

Input:

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

Output:

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

Examples:

in:

0 *

out:

*

explanation:

2**0=1

in:

1 *

out:

*
* *

in:

2 *

out:

*
* *
*   *
* * * *

Winner:

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

Hint:

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

Answer 6

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

---

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

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

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

stick tip stand 
--x-- >   -5

The stick

---

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

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

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

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

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

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

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

The Tip

---

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

The Stand

---

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

Execution of the kebab

---

You can't execute a kebab without eating it!

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

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

TODO

---

• Add test cases.

• Clear a few things up.

• Make the description of execution a bit clearer?

Answer 7

Nearest neighbors in a square lattice

code-golf sequence square-lattice

Premise

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

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

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

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

Task

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

Rules

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

Here are some 1-indexed test cases:

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

Answer 8

Breaking into 3 Palindromes:

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

Challenge

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

Examples

input: 5
output: 0,0,5

input: 1234
output: 1001,222,11

input: 3141592
output: 2200022,926629,14941

Answer 9

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

Background

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

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

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

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

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

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

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

Challenge

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

• \$A, B, C, O\$: three vertices and circumcenter,
• \$M_a, M_b, M_c, G\$: the side midpoints and centroid,
• \$H_a, H_b, H_c, H\$: three feet of altitudes and orthocenter,
• \$T_a, T_b, T_c, I\$: three feet of internal angle bisectors and incenter.

Out of the 139 problems, some are solvable by construction, but some are not. The problem we'll tackle here is problem 47, where the given points are:

• \$A\$: a vertex.
• \$H_a\$: the foot of the altitude on side \$a\$; that is, the opposite side of the vertex \$A\$.
• \$T_b\$: the foot of the bisector of angle \$B\$.

Given these three points, recover the other vertices \$B\$ and \$C\$.

Scoring & Winning criterion

Every usage of the six basic constructions (shown above) counts. For the line intersections, creating each point adds 1 score, e.g. if you need both intersections of two circles, you get 2 score from the step.

The solution with the lowest score wins.

Scoring example

Task: Construct the midpoint of two points \$A\$ and \$B\$.

Solution:

• Draw circle \$C_1\$ with center \$A\$ going through \$B\$. (+1)
• Draw circle \$C_2\$ with center \$B\$ going through \$A\$. (+1)
• Draw two intersections \$X, Y\$ of two circles \$C_1\$ and \$C_2\$. (+2)
• Draw line \$f\$ going through the two intersections. (+1)
• Draw line \$g\$ going through the two given points. (+1)
• Draw the intersection \$M\$ of \$f\$ and \$g\$. (+1)

The score of this construction is 7.

Tools

GeoGebra is a free online geometry tool. In addition to basic and advanced constructions, it has construction protocol feature which clearly shows the steps used to create the final image. For the above example task, the construction protocol looks like this:

Out of 9 steps in total, the points \$A\$ and \$B\$ are given, so we can confirm that seven steps are taken for this particular construction.

It also supports scripting (in GGBScript and JS) for those who want to view this challenge as code-golf or atomic-code-golf. Among many geometry commands, the Prove and ProveDetails commands may help you identify if a particular construction is indeed correct.

Notes

I'm using a relatively easy problem here, in order to see how this new challenge type is received. If it goes well, I'll propose some harder and open-ended problems later.

---

Meta

• Is this actually on-topic on PPCG? I'm asking this since this is the first challenge of its kind. I'll assume on-topic unless someone says otherwise on this meta question.
• Maybe we need to tweak the difficulty of the challenge at hand. Is it too easy or too hard? Any other suggestions? I picked Wernick's list because it's not something you may see on Euclidea or similar, and the optimal (or elegant) solutions for many of the problems are not yet known. I'll go for the task this time, and try to ramp up in subsequent challenges.

Answer 10

The max() is not enough

The max() is not enough

Answer 11

Formulize the sum: Faulhaber's formula

code-golf math polynomials sequence

Sums of the form Σkⁿ over k in 1..x can be turned into a polynomial of x whenever n is a natural number.

Examples

Σ1 = x
Σk = (1/2)x²+(1/2)x
Σk²= (1/3)x³+(1/2)x²+(1/6)x

Criteria

You will take n as a non-negative integer input and output the coefficients in reduced fraction form of the resulting polynomial from leading coefficient down to the last non-zero coefficient.

This is code-golf, shortest code wins.

Test cases

0 #=> 1
1 #=> 1/2 1/2
2 #=> 1/3 1/2 1/6
3 #=> 1/4 1/2 1/4  0
4 #=> 1/5 1/2 1/3  0 -1/30
5 #=> 1/6 1/2 5/12 0 -1/12

(extra spacing here is just for clarity and is not necessary.)

Answer 12

The Hungry Moose

code-golf

Inspiration.

Moose face harsh conditions during the winter. According to one source:

Their winter foods are lower quality than what they eat in summer and provides less energy, consequently, they need to eat more of it. During harsh winters, having both extreme cold temperatures and deep snow, moose expend more energy than they take in and many can starve.

Challenge

At noon on day 1, a hungry moose starts at a food source (the top left corner). Each morning, the moose may either walk to any 8-adjacent square or stay in place. Each evening, the moose clears the food and snow from its location (adding its net nutritional value to its calorie store and setting that value in the array to 0), and before the end of the day loses 1 calorie to the extreme cold.

The moose dies when its calorie store falls to 0 or below at the end of a day. In particular, if the value at the upper-left corner is 1, 0, or negative, the moose dies on day 1.

Input

A 2D array of integers. Negative numbers represent calorie-negative deep snow.

Output

The maximum number of days the moose can survive (counting day 1 as a full day).

Test cases (add)

6 0 -2 3
0 0 -5 -5
0 0 -1 3
8

42 -100 1
-100 -100 2
3 4 5
42

5 -3 1
1 -9 9
12

Answer 13

Extremely small data compressor

In 2014 Jarek Duda at Purdue University wrote a paper containing several ideas for encoding computer data, entitled “Asymmetric numeral systems: entropy coding combining speed of Huffman coding with compression rate of arithmetic coding". The paper is available at Cornell University Library’s ArXiv project: https://arxiv.org/abs/1311.2540

One of the many fascinating things about this paper is that it begins by describing an extremely simple data compression algorithm, using the concept of the "Uniform asymmetric binary systems (uABS)". In fact, it is so simple, that you can implement it in only a few lines of code! Basically it attempts to interpret a sequence of input bits as a single integer - but by interpreting that integer using an alternative to our place-value binary number system, one can "shrink" the size of the input data. In other words, more 'likely' sequences of data will tend to map to 'smaller' integers.

Challenge

You will implement the simple uABS compression algorithm, so that given a sequence of 0s and 1s, your program will compress them into a (usually) smaller sequence of 0s and 1s.

Pseudocode

The algorithm in psuedocode is as follows:

   Begin with an integer X, and set it to 1
   The input data is a sequence of symbols, each 0 or 1, called Input
   Find the probability P that any given symbol in Input is 1
   For each symbol S in Input,
      set X to the output of the function Encode( X, S, P )
   Output the final integer X as a sequence of symbols, 0s and 1s
   End

The Encode function itself can be described as follows:

$$ C(x,s,p)= \left\{ \begin{array}{11} \big\lceil\frac{x+1}{1-p}\big\rceil-1 & \mbox{if } s = 0 \\ \big\lfloor\frac{x}{p}\big\rfloor & \mbox{if } s = 1 \end{array} \right. $$

Where

$$ \begin{array}{11} C \text{ is the encoding function} \\ s \text{ is a symbol, either 0 or 1} \\ x \text{ is an integer} \\ p \text{ is the probability that any symbol in the Input data is 1 } \\ \text{ (the number of 1s divided by the total number of symbols)} \\ \lceil \rceil \text{ is the mathematical ceiling function } \\ \lfloor \rfloor \text{ is the mathematical floor function } \end{array} $$

Input and output format, notes, goofs and gaffes

• The input is a sequence of symbols, each symbol being 0 or 1, in any method that is available in your chosen language. Examples include a sequence of ascii characters '0' '1', an array of integers, etc.

• The output will be a sequence of symbols in the same format as the input sequence. The output sequence represents the compressed version of the input data.

• Empty input data has undefined behavior.

• Input data containing only 0s has undefined behavior.

• When testing, note that some times input data may not be shrunk, and sometimes will grow. This typically happens when the number of 1s and 0s is relatively even. Data with an unbalanced number of 0s and 1s results in better compression.

• You may assume that the number of symbols in the output is less than or equal to the number of bits in your language's largest integer type. The test cases outside this range can be ignored for your language.

• Note that if you are trying to test this by 'decoding' or 'decompressing' the compressed data, and compare it to the original, one would have to store additional information, such as the length of input and probability P, but for simplicity this has been left out of the challenge.

Example Input and Output

Short examples:

Input             Output    
10                101
10010100000       1011101001
1111              1
11111111111       1
10000000          11011
10011111010101    10110000100101    

Longer examples:

Input  11111110110111110111111111011111
Output 11111000011110110

Input  000000000001000000010000000000001100000000001
Output 1110000101100111000011111

Input  000000000001000000010000000000001100000000001000000000000000000000000000000000000000000000000000000000000000001
Output 1010100110111110010111011110110101010

Scoring

• Have fun!

• The program with the fewest number of characters wins!

Answer 14

Inscriptio Labyrinthica

In the burial place of King Silo of Asturias there is an inscription that reads SILO PRINCEPS FECIT (King Silo made this).

The first letter is found in the very middle, and from there one reads by going in any non-diagonal direction radiating outward. The final letter is found on all four corners. In this challenge, you'll generalize the process to make them.

Input

A string (or equivalent), and an integer. You may make the following assumptions about the input:

• The string will have an odd length.
• The integer will be an odd number between 1 and one less than twice the length of the string.

Output

An inscriptio labyrinthica for the string, using the integer for the height (see models). Output should be each letter with no spaces, line break as default to your system/language.

Test cases

Note that an input of 1 or (length * 2 - 1) will result in a horizontal or vertical palindrome.

 Input: FOO, 3    Input: BAR, 1    Input: BAR, 3    Input: BAR, 5

Output: OOO      Output: RABAR    Output: RAR       Output: R
        OFO                               ABA               A
        OOO                               RAR               B
                                                            A
                                                            R

 Input: ABCDE, 5   Input: ABCDE, 3   Input: *<>v^, 3

Output: EDCDE     Output: EDCBCDE           ^v>v^
        DCBCD             DCBABCD           v><>v
        CBABC             EDCBCDE           ><*<>
        DCBCD                               v><>v
        EDCDE                               ^v>v^

Scoring

This is code-golf so shortest answer in bytes wins. Standard loopholes forbidden.

(I feel like I've seen one similar, but searching around I couldn't find it, and I happened to be reading about this king when I got the idea).

Questions

In my original proposal, I had listed as a bonus to draw reading lines, but feedback was bonuses in code golf are discouraged. I still like that idea and am thinking about integrating it as a a main part of the challenge, but don't know if that would over complicate it or actually make it more interesting. The output for REI, 3 in such a case would be

I←E→I
↑ ↑ ↑
E←R→E
↓ ↓ ↓
I←E→I

The idea is that it would prevent simple flipping of data after calculating a quarter or half of the but still perhaps allow for some creative ways (I can think of some creative ways to do it shortly in some languages, but maybe it'll be overly complicated for others).

Answer 15

Golf the truth and null values

In many programming languages there is a null and/or other special values. Sometimes they don't follow the normal rules of boolean operations. They may not even agree with the values of the same name in other languages.

Here are some different kinds of the "extended" boolean values, either borrowed from some languages or invented myself:

• False.
• True.
• Absent. All operations between absent and another operand return the other operand.
• Whatever. All operations between whatever and another operand returns whatever (itself).
• Partial. If the result can be decided using the other operand, return that. Otherwise return partial (itself).
• Error. An error as the first operand works like whatever, and an error as the second operand works like partial, except that "itself" means error. It has higher precedence than whatever and partial.

Your task is to define all these values in your language, and the 2 operations and or.

To be clear, the 2 operations should work exactly as in the following tables. The left column represents the first operand, and the top row the second operand.

and F T A W P E       or F T A W P E
  F F F F W F F        F F T F W P E
  T F T T W P E        T T T T W T T
  A F T A W P E        A F T A W P E
  W W W W W W W        W W W W W W W
  P F P P W P E        P P T P W P E
  E E E E E E E        E E E E E E E

Rules

You could use anything distinct and consistent to represent these values. You don't have to use a truthy value to represent true, or a falsy value to represent false. You are allowed and encouraged to use values that contain useful code, i.e. this loophole is not forbidden.

You are allowed to use actual errors or exceptions to represent some of the values. In this case the definition of that value should throw the same error, instead of represent the caught error. But the caught errors or the output messages should be distinct and consistent. Alternatively, you may choose to include STDERR in the output of your code, and use the printed message string as a normal value.

You may choose to pass functions generating and returning the values but doing nothing else to your code as input, in place of the values themselves, without counting the extra code.

You may use different ways of input/output for different values, as long as it is consistent for each kind of value, and it is possible to tell apart the first and the second operand.

You are allowed to use builtin functions and operators without boilerplate, in any argument order, even if you cannot save them in something callable in your language.

There could be some common code shared by all the 8 definitions and appear only once as header/footer. Other than that, the 8 definitions of operations and values must work independently from each other. The only way you can call something defined in the values in the operations is through a valid input method (e.g. you cannot set a variable in a value and read it in an operation).

Your score is the length of common code * 12 + the total length of the 2 operations * 6 + the total length of the values. Smallest score wins. The length of a value is either the length of the code generating it, or the length of itself unquoted if all the values are strings and you choose this way.

---

Abandoned rules

You are allowed to use operators, or chains of operators and values to represent the 2 operations, even if you cannot save them in something callable in your language. You may require the operands to appear at specific positions, but each operand must appear exactly once and be grouped together. You may choose whether to save operands in variables previously, and don't count the assignment if it doesn't add new information in the assignment (e.g. by changing its type). This makes it possible to use the built-in operators with short-circuit evaluation in languages that don't allow redefining them and preserve this characteristic, and may also make it shorter in some other languages.

Previous scoring: total length of the 2 operations * 50 + the total length of the values.

Possible follow-up

Original title: All the weirdness about the nulls

Extended tables including Valid in a previous version, Reverse aka Opposite by Zgarb, and Possible.

and T F N O W E V R P     or T F N O W E V R P
  T T F T O W E ? F T      T T T T T W T T T T
  F F F F F W F F F F      F T F F O W E ? T F
  N T F N O W E ? ? ?      N T F N O W E ? ? ?
  O O F O O W E ? O O      O T O O O W E ? O T
  W W W W W W W ? W W      W W W W W W W ? W W
  E E E E E E E ? E E      E E E E E E E ? E E
  V T F ? O F F ? ? ?      V T T ? T F F ? T ?
  R F F ? O W ? ? ? ?      R T T ? O W ? ? ? ?
  P T F ? O W ? ? ? ?      P T F ? T W ? ? ? ?

Other potential additions:

• Default, that is opposite to Opposite.
• Merge Possible with Valid.

Sandbox questions

1. Will this be too easy in some languages that already have all of them?

   In languages that has True defined to be -1 and unifies bitwise and logical operations, most integers would works as Partial. GCD/LCM in APL is similar to this. SQL null is Whatever Partial. Most languages that has shortcut evaluation has errors as Error. Not sure about Absent, though.

   (Maybe the easiest way to find out is to post this question. It doesn't make the answer bad. But it's just some consideration in the sandbox for me to decide whether I'll post a stronger version.)

2. Allowing "operators and chains of operators" seems to open a can of worms. Should I just remove this rule?

Answer 16

Knight's tour

code-golf chess

---

A knight's tour is a sequence of moves of a knight on a chessboard such that the knight visits every square only once. For those who are not aware of how knights in chess work, knights are capable of moving in an L shape:

Tours generally apply to a regular chessboard of size \$8\$ however, it can be calculated for other sizes. For example, for a chessboard of size \$5\$, a possible knight's tour is:

Each grid size has quite a few combinations, for example, when \$n = 5\$, there are \$1728\$ possible tours and for a regular chessboard (where \$n = 8\$), there are \$19591828170979904\$. This is OEIS A165134.

Challenge

Write a program/function that takes a grid size \$n\$ and outputs a possible valid board of integers.

Specifications

• Standard I/O rules apply.
• Standard loopholes are forbidden.
• \$n > 4\$
• This challenge is not about finding the shortest approach in all languages, rather, it is about finding the shortest approach in each language.
• Built-in functions that compute this sequence are allowed but including a solution that doesn't rely on a built-in is encouraged.
• Explanations, even for "practical" languages, are encouraged.

Test cases

Yet to come.

Answer 17

Babel on and on (working title...)

Background

Babel is a cornerstone of modern web development. It takes Javascript using new or proposed ECMAscript features and "transpiles" it into an older language version, so that browsers can run it without updates. In order to do this it inserts its own shim methods, and own custom transforms.

The Challenge

Your objective is to write the Javascript code which produces the largest babel output in characters. Your code must be less than or equal to 128 bytes in length

Babel has an online, interactive compiler which you can access HERE. It's highly recommended that you use this to form your answer. If you work locally, you are restricted to modifying only the settings that the babel website allows you to modify.. There is a guide on installing babel at the end of the question.

Rules

• For consistency, you may use a Babel version between 7, but not above 8.* (when it eventually comes).
• You may change the interactive REPL's settings, source type, presets, options, and env-presets. You may change these settings locally if you are using a local installation of babel.
• You may only provide one input file.
• You may not exceed 128 bytes in your input file.
• You may not add your own plugins.
• You may not use the loophole listed below, or any of the standard loopholes.
• You may not use error output as a result. babel must transpile the code successfully under one of the allowed configurations.
• Neither your input or output need to run, or halt. The compilation just needs to output something.

Examples

41 in, 1075 out

{t: [...(function*(){let [a,b]=[1,2]})]}

32 in, 1101 out

export class b{d=function*(){}}

125 in, 7336 out

const b = function*(){return function*(){return function*(){return function*(){return function*(){return function*(){}}}}}};

Scoring

You must provide both the code and the settings you are using. For users of the online REPL, a link with the settings set in the URL suffices. The answer with the largest output with an input less than or equal to 128 bytes wins. Unlike many challenges of this nature, settings do not cost any bytes of input.

Setting up a local environment (OPTIONAL)

Most of the people doing this challenge will probably use babel's online transpiler to complete it. In the event that the website is taken down in the future or made inadequate for the challenge, it can be completed locally. Make a folder for the challenge, and in a shell in that folder, try something like the following:

Install Babel (globally - you could do it locally)
sudo npm install -g @babel/core @babel/cli
Set your .babelrc with a preset (in this case env)
echo '{"presets": ["@babel/preset-env"]}' > .babelrc
Install babel's dependencies
npm install --save-dev @babel/preset-env @babel/core

Then, given an input file test.js, you can figure out your output score with

babel test.js | wc -c

Happy Hunting!

Questions

This is my first time ever posting one of these. Does everything look on the up-and-up?

Also, should this incorporate "the less characters of input, the better?". I kept trying to think of ways to reward a large output for a small input, but every way I considered changed the tone of the challenge significantly.

Also also, I know that codegolf users don't like being constrained to one language. Is this bound to be an exception or will that stop the question in its tracks?

Proposed Tags: [BUSY BEAVER], [Javascript], [CODE CHALLENGE]

Answer 18

Castilian Numerals

A little known (but actually real) number system are the Castilian numerals. They were an odd mix of a digital and positional counting system used in Spain in the late middle ages. There are certain qualities about them, however, that make them not entirely straight forward to generate when you have lots of them in a group, in particular the fact they would be aligned by thousands places. Your challenge will be to print a vertical list of numbers, correctly spaced.

Description of the Numerals

A Castilian numeral is, in effect, a Roman numeral, but only uses 1-999, uses additives for 4 (IIIJ), 9 (VIIIJ), and 900 (DCCCC), and subtractives for 90 (XC) and 400 (CD). Both methods were commonly used for 40 (XL, XXXX). Additionally, final Is were written as Js, such that the sequence 1-6 goes J, IJ, IIJ, IIIJ, V, VJ. (This means standard Roman numeral generators will likely not be much help.) They were generally written lowercase, but for this challenge we'll use all uppercase.

For values under between 1-999, the fact that the letters indicated numerals was made clear by the presence of a symbol that looks like a U. Generally the numerals themselves were right aligned:

1          U           J
2          U          IJ
999        U DCCCXCVIIIJ

For values between 1000-999999, everything we would place to the left of the comma would be rendered as if it were its own independent 3-digit number and romanized, and the reminder placed to the right, such that

  1,000    J U
  1,001    J U          J
 21,030  XXJ U        XXX
500,444    D U CDXXXXIIIJ

For values 1,000,000-999,999,999, an additional separator was used, Q^to, but for our purposes, we'll just use Q. It would only be used if the number was over 1,000,000, unlike the U that always separated it.

  1,000,000       J Q       U
  1,000,001       J Q       U            J
  1,001,000       J Q     J U
  1,001,001       J Q     J U            J
123,456,789  CXXIIJ Q CDLVJ U DCCLXXXVIIIJ

As should be noticed, within each grouping of three (arabic) digits, everything is right aligned, with the thousands/million separators all in alignment. Because 0 didn't exist, it would just be left blank.

Input

A sequence of integers in whatever format you feel gives you the best advantage (a list, an array, a series, etc). You may assume that the integers are between 1 and 999,999,999.

Output

A printed list of Castilian numerals, properly aligned on different lines. Note the restrictions on 4/9: mandatory additives are 4,9,900; mandatory subtractives are 90 and 400; 40 is valid either way. The numerals for 1-999 should be right aligned, with a single space on either side of Q or U (there may be padding spaces, but the single longest numeral in each grouping will have the single space). Newlines may be whatever is native to your system/language.

Rules

This is code golf. Fewest bytes wins. Standard loopholes forbidden.

Test cases

Comments/observations are given after # and not part of the output.

Given: 1,2,3
U   J   
U  IJ
U IIJ   # one space between U and I

Given: 1,1000,10,100
  U J
J U     # trailing space not required
  U X
  U C

Given: 123,4,5678,111111111,90,12345,6789012
                U    CXXIIJ
                U        IV
              V U DCLXXVIIJ   # single space between U and the longest numeral
CXJ Q       CXJ U       CXJ   # Q only appears if >= 10^7
                U        XC
            XIJ U  CCCXXXXV   # also valid CCCXLV 
 VJ Q DCCLXXXIX U       XIJ   # single space between Q and the longest numeral

Answer 19

Polyglot wrappers

Many polyglots are a disastrous mess of unmaintainable code. Let's make this different.

Challenge

Make a polyglot "wrapper" such that code from two or more languages may be embedded in the file without modification.

Example

Consider the following polyglot wrapper for Bash and Python:

'''true'
B
exit 0
#'''
P

This wrapper can be used such that B can be replaced by an arbitrary bash script, and P can be replaced by an arbitrary python script.

After the scripts have been injected into the wrapper, running the resulting polyglot via either interpreter (bash or python) will result in functionally identical behavior as the original input scripts.

Rules

1. Your wrapper must support the injection of 2 or more languages
2. Your wrapper can use arbitrary markers for the string->script replacement
3. The markers must be at least 1 byte in size (no line number tricks)
4. Assume the replacement will be done by first replacing all markers with sufficiently long and random data, such that conflicts between the marker literals and contents of the input code cannot exist. However, your markers cannot conflict with the contents of the wrapper itself.
5. The behavior of the original input programs must not be altered by the wrapper. Ex: an input program that returns 0 must return 0 when run from your wrapper. An input program that crashes must still crash.
6. The winner is the polyglot wrapper that supports the most languages, with a tie breaker of smallest size (in bytes).
7. Allowances shall be made for a program that accesses itself on disk. Obviously no polyglot wrapper could correctly return identical output for a script that outputs its own file size.

Question for the sandbox

Is this sufficiently unique and understandable? Are there any loopholes I haven't covered?

Answer 20

Hexagonify™ a String Block code-challengestringascii-art

Answer 21

Rennab

Reverse banneR

In the language of your own choosing write a program or function that takes as input the output of the super-handy-for-the-farsighted tool banner. And simply outputs the original text.

Example 1a of banner output on Linux:

> banner 'Code Golf'

   XXXX              XX                    XXXX            XX       XX
  X    X              X                   X    X            X      X
 X                    X                  X                  X      X
 X        XXXXX   XXXXX   XXXXX          X        XXXXX     X     XXXX
 X       X     X X    X  X     X         X       X     X    X      X
 X       X     X X    X  XXXXXXX         X   XXX X     X    X      X
 X       X     X X    X  X               X     X X     X    X      X
  X    X X     X X    X  X     X          X    X X     X    X      X
   XXXX   XXXXX   XXXXXX  XXXXX            XXXX   XXXXX   XXXXX   XXXX

Example 1b of rennab program that runs on Linux and takes input from stdin as lines of strings, and outputs to stdout, and supports the characters: [' ', 'C', 'G', 'd', 'e', 'f', 'l', 'o']:

> banner 'Code Golf' | rennab
Code Golf

Example 2a of banner output on Linux:

> banner ':-)'


                   X
                    X
                    X
    X                X
                     X
         XXXXXXX     X
                     X
                     X
    X               X
                    X
                   X

Example 2b of rennab program that runs on Linux and takes input from stdin as lines of strings, and outputs to stdout, and supports the characters: [':', '-', ')']:

> banner ':-)' | rennab
:-)

Choose what ever characters (minimum of 3) you want to support but that effects your score (see Rules below).

Rules

• Program or function - your choice.
• Input the output of banner in whatever format you'd like (eg 2d array of characters, list of strings, reading from stdin straight from the horse's mouth, &c).
• For this challenge we'll use Cedar Solutions' open-source GNU/GPL banner implementation common on Linux. Prints horizontally only with a fixed size.
• Output the original text in whatever format you'd like, return character at the end optional (eg as a string, a list of characters, as output to stdout, &c).
• You can assume only the characters supported are input.
• You must support a minimum of 3 characters.
• Score is calculated by this formula (where \$n\$ is the number of code bytes and \$c\$ is the number of characters supported): \$n - 8c\$.
• Scores can be negative.
• No standard loopholes.
• Lowest score wins.

Questions

• Has this been done before?
• Is the score formula any good? Any and all suggestions welcome.
• Is the question any good? Any and all feedback welcome.

Answer 22

Reversed Iota's code-golf

I didn't invent this challenge, but I find it very interesting to solve.

For every input number, e.g.:

4

Generate a range from 1 to that number:

[1 2 3 4]

And then, for every item in that list, generate a list from 1 to that number:

[[1] [1 2] [1 2 3] [1 2 3 4]]

Then, reverse every item of that list.

[[1] [2 1] [3 2 1] [4 3 2 1]]

Notes:

• 1 being a loose item is allowed, since flattening will not matter with this anyway.
• To preserve the spirit of the challenge, the range has to be 1-indexed.

Answer 23

Is it a doubling sequence?

Posted here:

Is it a doubling sequence?

Answer 24

Posted to main.

Answer 25

Is it a Happy Number? code-golf decision-problem

A repost of this challenge (if I got the policy right).

Given a single positive integer (which can also be taken as a list of digits or a string), output whether the number terminates at 1 . Truthy/falsy follows the language's convention, or you can choose exactly one value for truthy and another for falsy. (This sequence is A007770.)

Your program should theoretically support all non-negative integers; however, if your language doesn't support unbounded integers, you may only support integers up to 2147483647.

Procedure

Suppose you have the number 193.

• Square every individual digit in the number. Therefore the number's individual digits becomes:

[1] [81] [9]

• Sum all these individual digits:

92

• Repeat this procedure until it stabilizes at 1 or a 37-cycle like the following:

37-58-89-145-42-20-4-16-37

It has been shown that the procedure will always produce either one of these two outputs.

Test cases

Here is a sample program generating the test cases. Here is a step by step reduction of all input between 1 and 100.

1 -> true
2 -> false
3 -> false
4 -> false
5 -> false
6 -> false
7 -> true
8 -> false
9 -> false
10 -> true
11 -> false
12 -> false
13 -> true
14 -> false
15 -> false
16 -> false
17 -> false
18 -> false
19 -> true
20 -> false
21 -> false
22 -> false
23 -> true
24 -> false
25 -> false
26 -> false
27 -> false
28 -> true
29 -> false
30 -> false
31 -> true
32 -> true
33 -> false
34 -> false
35 -> false
36 -> false
37 -> false
38 -> false
39 -> false
40 -> false
41 -> false
42 -> false
43 -> false
44 -> true
45 -> false
46 -> false
47 -> false
48 -> false
49 -> true
50 -> false
51 -> false
52 -> false
53 -> false
54 -> false
55 -> false
56 -> false
57 -> false
58 -> false
59 -> false
60 -> false
61 -> false
62 -> false
63 -> false
64 -> false
65 -> false
66 -> false
67 -> false
68 -> true
69 -> false
70 -> true
71 -> false
72 -> false
73 -> false
74 -> false
75 -> false
76 -> false
77 -> false
78 -> false
79 -> true
80 -> false
81 -> false
82 -> true
83 -> false
84 -> false
85 -> false
86 -> true
87 -> false
88 -> false
89 -> false
90 -> false
91 -> true
92 -> false
93 -> false
94 -> true
95 -> false
96 -> false
97 -> true
98 -> false
99 -> false

Answer 26

Hamming distance traveling salesman problem fastest-code

The Hamming distance between two strings is the number of positions they differ at.

You are given a set of binary strings. The task is to find the length of the shortest route that visits all of them at least once and ends where it started, in a metric space where the distance between two strings is the Hamming distance between them.

The sandbox proposal for this used to be about Levenshtein distance, but then I noticed that somebody claims this is NP-complete as well...

Let \$N\$ be the number of input strings and the string length. There are 3 test cases for every \$N\$. The strings are created from random bits, and the random bits are obtained from an acceptable random number generator. A RNG is acceptable if the program's performance does not rely on me not replacing it with a RNG I like more.

A program's score is the largest \$N\$ it can correctly solve all 3 tests for within 60 seconds. The higher the score, the better. A tiebreaker is the posting time (older answer wins)

Submissions will be timed on two devices: a laptop with an AMD Ryzen 5 2500U CPU and integrated graphics and a PC with an old AMD FX-4350 CPU, but a (cheap but relatively modern) AMD Radeon RX 550 GPU. Of course, your score is the higher one.

Answer 27

Metagolf: Catlike Piet

The goal of this is to write a catlike program, which would be executed (in a Unix environment, though you needn't stick to that) by the following:

yourprogram < file > output
piet output

where piet output writes the contents of file to stdout. That is, you're to generate a Piet program which prints the input to yourprogram.

One-liners

Straight line programs can be written in Piet... in straight lines. If you're willing to take a hit to your score, your output can take the form of a string of commands:

=  none (continue color block)
|  push
^  pop
+  add
-  subtract
*  multiply
/  divide
%  mod
~  not
>  greater
.  pointer
\  switch
:  duplicate
@  roll
$  input number
?  input character
#  output number
!  output character

which is trivial to convert to a Piet program with the following (partially golfed) Python code:

def P(s):
 h=v=0;l=len(s)+1;R="P3 %i 2 255 192 0 0 "%(l+2)
 C=[1,3,2,6,4,5];V=[0,192,192,255,0,255]
 for x in map("=|^+-*/%~>.,:@$?#!".find,s):
  C=C[x//3:]+C[:x//3];V=V[x%3*2:]+V[:x%3*2]
  for i in [1,2,4]:R+="%i "%V[(C[0]//i)%2]
 return R+"255 "*4+"0 0 "+"255 "*l*3+"255 0 0 "*2

The dimension of said program is (n+3) x 2 if there are n characters in the string.

Scoring

Your code will be judged on the maximum dimension of the images that it outputs.

• Part 1: Take the maximum score taken over all ascii codes (that is, single-character inputs), discounting EOF.

• Part 2: Take the score for the input "Hello. My name is Inigo Montoya. You killed my father. Prepare to die."

Your score is the product of the scores in part 1 and part 2.

Punishment: Double your score if you write one-liners as above (that is, if you don't output an image).

Bonus: If your program is written in Piet, take the square root of your score above.

Answer 28

Chess move

The Challenge

Write a program that gets a string containing a chessmove and a chessboard as input, and then outputs the chessboard.

Requirements

The chess move will have this format:

<from square><to square>[<promoted to>]

Examples:

d2d4
f8g7
a7a8R

The chessboard format is not fixed, but there must be a 1 to 1 relation between the board and the string to represent the board. Also the format of the input must bet the same as the format of the output. Two suggestions of what it could look like:

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR

rnbqkbnr pppppppp 00000000 00000000  00000000  00000000 PPPPPPPP RNBQKBNR

It is not required to store anything except the location of the pieces, and validity of moves can be assumed.

Scoring

Base score is character count (assuming your program can move pieces for all moves)

Bonus multipliers:

• If the program updates the promoted piece, divide by 2
• If the program also moves the rook when castling, divide by 2
• If the program also removes the pawn when capturing en passent, divide by 2

The moves, and castling & en passent in particular are explaned on Wikipedia.

So basically writing a 100 character solution for the base problem gives the same score as an 800 character solution with all bonus multipliers.

Examples

If you would choose to use one of the board formats above, your input would look like one of these strings:

e2e4 rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR

e2e4 rnbqkbnr pppppppp 00000000 00000000  00000000  00000000 PPPPPPPP RNBQKBNR

Your corresponding output string would then be one of these:

rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR

rnbqkbnr pppppppp 00000000 00000000  0000P000  00000000 PPPP0PPP RNBQKBNR

Answer 29

code-golf game board-game algorithm

Black Box

Your task is to analyze a given situation for the game Black Box. Given a sequence of guesses and answers, your program is to either print the solution or suggest the next move.

The game

The board consists of 8×8 cells, with edges labeled like this:

I'll probably create nice images here, particularly to make sure that the squares of the board are really square.

 abcdefgh
i        I
j        J
k        K
l        L
m        M
n        N
o        O
p        P
 ABCDEFGH

The player shoots rays into the interior of the box, where they might get deflected, reflected or absorbed. He is told the position where the ray leaves the black box again, and from that has to deduce the positions of 4 atoms inside the black box.

I'll have to include more of the game rules here, but for now see Wikipedia.

Input and output

Input is a sequence of line, each consisting of two characters. The first denotes the point where the ray of light enters the black box, the second the place where it comes out again. In the case of a reflection, both characters will be equal. In the case of a hit, the second character will be -.

If the input is enough to fully determine the locations of the atoms, then output should be four lines giving the coordinates of each atom. The lines should be two lower case characters each, the first giving the row and the second giving the column of the found solution. The atom positions must be printed in lexicographical order.

If the input is consistent with more than one set of atom positions, then the output should consist of a single line containing a single character, which is the location where the next ray should be shot. That location has to be chosen in such a way that it can help find the solution. This is the case unless all of the atom positions consistent with the input so far would produce the same output for this next ray as well.

Your output has to be terminated by a newline character.

Examples

Let's take the atom configuration the Wikipedia article uses as an example as well:

 abcdefgh
i        I
j        J
k O    O K
l        L
m        M
n   O    N
o        O
p      O P
 ABCDEFGH

If the input were

cf
D-
Em
HH
Co

then the output should be

kb
kg
nd
pg

but if the input were only

Em
HH

then the output might be for example

K

Scoring

This is code golf, so shortest answer wins. However, I'll only accept answers which are practical in so far as they compute their result in reasonable time. I'd say no more than five minutes on my system where I'll evaluate the answers, and I'll simply hope that correct solutions will be much faster and incorrect ones much slower, so that the speed of my system doesn't make a difference. A submission which gives a wrong answer for one of my test cases will be disqualified until it gets fixed. I will probably point out the problem in a comment to that post.

Answer 30

Create a program with "exact repetition" in its source code

The task is to create a program, with the following restrictions placed on the printable ASCII characters in the source code: choose some k > 0.

• Every non-alphabetic character has to appear exactly k times.
• Every alphabetic character has to appear at most k times.
  • This rule differs from the former in order to avoid boring dummy identifiers while still making it a challenge to choose good library functions to call.

Character set definitions used:

• Non-alphabetic characters are !"#$%&'()*+,-./0123456789:;<=>?@[\]^_{|}~ and '`' (backtick).
• Alphabetic characters are ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz.

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

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

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

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

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Example answer (C)

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

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

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