# Sandbox for Proposed Challenges

This "sandbox" is a place where Code Golf users can get feedback on prospective challenges they wish to post to main. 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.

Sandbox FAQ

## Posting

Write your challenge just as you would when actually posting it, though you can optionally add a title at the top. You may also add some notes about specific things you would like to clarify before posting it. Other users will help you improve your challenge by rating and discussing it.

When you think your challenge is ready for the public, go ahead and post it, and replace the post here with a link to the challenge and delete the sandbox post.

## Discussion

The purpose of the sandbox is to give and receive feedback on posts. If you want to, feel free to give feedback to any posts you see here. Important things to comment about can include:

• Parts of the challenge you found unclear
• Problems that could make the challenge uninteresting or unfit for the site

You don't need any qualifications to review sandbox posts. The target audience of most of these challenges is code golfers like you, so anything you find unclear will probably be unclear to others.

If you think one of your posts needs more feedback, but it's been ignored, you can ask for feedback in The Nineteenth Byte. It's not only allowed, but highly recommended!

It is recommended to leave your posts in the sandbox for at least several days, and until it receives upvotes and any feedback has been addressed.

## Other

Search the sandbox / Browse your pending proposals

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# Climbing up slippery stairs code-golfmathcombinatorics

## Challenge

You're standing in front of a stairway with $$\n\$$ stairs in total. (If you label each staircase $$\1,\cdots,n\$$, the starting point counts as the 0th staircase.) You can climb up $$\1,2,\cdots,k\$$ stairs at a time. But some stairs are slippery; if you step on it, it will cause you to slip backwards until you stand on a non-slippery one (or the starting point). In how many ways can you get to the $$\n\$$th staircase with exactly $$\s\$$ steps?

Task: Given the list of staircases of length $$\n\$$ marked with either "slippery" or "non-slippery" (you can choose any two consistent values) and the values of $$\k\$$ and $$\s\$$, answer the above question.

The $$\n\$$th staircase is guaranteed to be non-slippery, and you cannot move further than the $$\n\$$th. This implies that reaching the destination before you spend $$\s\$$ steps doesn't count.

For example, if the stairway is [non-slippery, slippery, non-slippery] and $$\k=2\$$, two possible first steps (climbing one or two stairs) will result in the same position (the first staircase), but count as two distinct possible moves. And if you try to climb one stair as the second step, you will end up not moving at all, but it still counts as a step.

You may assume $$\1 \le k \le n\$$ and $$\s \ge 1\$$. Some inputs may have no way to reach the destination at all; in that case, your code should output the value of zero for any value of $$\s\$$.

## Example and test cases

N means non-slippery, and S means slippery. 1-1-3 notation means that you can reach the top in three steps, trying to advance 1, 1, and 3 stairs at once.

N = [N, S, N, N]
k = 3
s = 1: answer = 0 (no way to climb 4 stairs at once)
s = 2: answer = 3 (1-3, 2-3, 3-1)
s = 3: answer = 4 (1-1-3, 1-2-1, 2-1-3, 2-2-1)

N = [S, S, N, S, S, N]
k = 4
s = 1: answer = 0
s = 2: answer = 2 (3-3, 4-3)
s = 3: answer = 8 (1-3-3, 1-4-3, 2-3-3, 2-4-3, 3-1-3, 3-2-3, 4-1-3, 4-2-3)


More test cases coming soon.

# ⧵begin{alignat} ... ⧵end{alignat} code-golfstring

Note: The title intentionally uses &#10741; (reverse solidus operator) instead of plain backslash, because otherwise MathJax would happily translate the entire title to... uh... a MathJax error box.

## Background

\begin{alignat}{n} ... \end{alignat} is a lesser known LaTeX/MathJax block that allows aligning multiple parts of multi-line equations.

\begin{alignat}{5}
A&=&B&\\
& &B&=&C&\\
& & & &C&=&D&\\
& & & & & &D&=&E
\end{alignat}


\begin{alignat}{5} A&=&B\\ & &B&=&C&\\ & & & &C&=&D&\\ & & & & & &D&=&E \end{alignat}

\begin{alignat}{5}
x&=&-3&a&-&2&b\\
y&=& 2&a&+& &b
\end{alignat}


\begin{alignat}{5} x&=& 3&a&-&2&b\\ y&=&-2&a&+& &b \end{alignat}

## Challenge

Implement "Poor Man's ASCII-Only Alignat", which tries to replicate the behavior of MathJax but in plain text. The spec of PMAOA is as follows:

• Let's define a "word" to be each part of a line delimited by the & character. A word can be empty, and the parts before the first & and after the last & also count as words.
• Given a multi-line string input, identify the 1st, 2nd, 3rd, ... word of each line.
• Right-align the 1st words of all lines, right-align the 2nd words of all lines, ..., and concatenate the aligned blocks horizontally. Padding is done with minimal amount of space characters. Trailing whitespace at the end of each line is optional.

Standard rules apply. The shortest code in bytes wins.

## Test cases

Coming soon.

• By saying align, is extra spaces allowed? For example, "a&b\ncd&e" -> "..a..b\n.cd..e"
– tsh
Nov 9 at 10:02
• @tsh No, the padding should be minimal. Nov 9 at 10:14

# What is the maximum value generated by interleaving?

INTERCAL has an interleave operator which does the following operation. Let left operand be asdf and right one qwer in binary, respectively. The operation produces a binary value aqswdefr.

INTERCAL internally treats data as unsigned integers, so the value of the eight-bit value represents 0 to 255 in decimal, inclusively.

If one operand has fewer bits than the other, the fewer one gets padded with zero before operation. So, asd interleaving with qwer is equal to 0asd interleaving with qwer, which is 0qawsedr: it represents 0 to 127 in decimal.

Also, INTERCAL has an extension that handles any bases. Let's assume if 3-base numbers are handled. If each operand has 1 and 3 digits respectively, the maximum value for each operand is represented as 2 and 222 in 3-base number, respectively. Interleaving them results in 020222, which is 188 in decimal.

Given an input of three unsigned integers, output the largest possible value generated by interleaving. The three integers are: number of digits for left operand, number of digits for right operand, and in what base those operands are described with.

## Restrictions

• Base shall be 2 or greater.
• Each operand has at least 1 digit.

## Rules

• In either function or a program.
• Standard I/O rules apply, as long as every input and output value is represented as same base or same representation.
• So varying output base is not allowed.
• If input is represented as a list-like format, any orders of arguments or input values are fine.
• No standard loopholes.
• Shortest code wins

TODO.

# meta

• Am I missing any appropriate tags yet?
• The I/O rules seem fine. I'd suggest changing the title to something like 'What is the maximum value generated by interleaving?' Also, 'output what the possibly largest value interleaving generates' -> 'output the largest possible value generated by interleaving'. Nov 12 at 4:14

# Constructing Solar Panels from Squares part 2 code-golfnumberoptimization

Thanks to all your generous contributions of code, my horde of minions can now precisely calculate how to construct solar panels of any size, but there's a problem.

The logistics department used these results to calculate how many square panels they would need for every size up to 1,000,000, which is way too many panels. As it turns out, larger panels are more expensive than cheaper ones, so I've decided we need to try to use the largest square panels we can wherever possible.

To make matters worse, my team of scientists tell me that we should avoid using multiple panels of the same size in our configuration, except for our tiny 1x1 panels, to make sure the panels don't fall apart.

## The Challenge

Given a positive integer n, output a list of square numbers that sums to n containing the largest squares possible such that no square number other than 1 appears multiple times.

A square number is any integer that is the result of multiplying an integer by itself. For example 16 is a square number because 4 x 4 = 16 This is A000290

For example: For n = 12, you could achieve the desired size with 4 panels of sizes [9, 1, 1, 1]. As 9 is the largest square possible in this configuration, this is the best answer. For n = 13, you can achieve the desired size with only 2 panels: [9, 4]

If n is a square number, the output should be [n].

## Input

A positive integer n representing the total desired surface area of the solar panels. Note that 0 is not positive.

## Output

A list of square numbers that sums to n containing the largest squares possible.

### Testcases

1 -> [1]
2 -> [1,1]
3 -> [1,1,1]
4 -> [4]
7 -> [4,1,1,1]
8 -> [4,4]
9 -> [9]
12 -> [9,1,1,1]
13 -> [9,4]
18 -> [16,1,1]
30 -> [25,4,1]
50 -> [49,1]
60 -> [49,9,1,1]
70 -> [64,4,1,1]
95 -> [81,9,4,1]
300 -> [289,9,1,1]
1246 -> [1225,16,4,1]
12460 -> [12321,121,16,1,1]
172593 -> [172225,361,4,1,1,1]


# Sandbox

I don't think this challenge is similar enough to part 1 to be considered a dupe, as while some answers from part 1 could be trivially modified to work for part 2, they would likely be out-golfed by better approaches.

That said I'm not sure how well-worded the output requirement is. a list of square numbers that sums to n containing the largest squares possible such that no square number other than 1 appears multiple times. feels poorly worded, but I'm not sure how I could word it better.

• The challenge is unclear. I think you copied part 1 but forgot to edit testcase and example of challenge
– okie
Nov 17 at 1:04
• such that no square number other than 1 appears multiple times - test cases don't agree. Nov 17 at 5:24
• I did generate new testcases when I wrote this, but I guess I messed up when putting them in. I'll re-run and update the testcases now Nov 17 at 22:15
• 8->4,4 having 2 4
– okie
Nov 18 at 0:43
• Am not sure if this question may be solved by modify the previous one trivially. But there would be many answer be very similar though. I'm not sure if it would be a duplicate to that one in such case.
– tsh
Nov 18 at 3:59
• @okie yeah, the problem is with the wording of the challenge, not the testcases. Not sure how best to word it... Nov 18 at 14:07
• So only the largest and 1 can appear multiple time?
– okie
Nov 18 at 23:27

# Fully matched numbers sequence

For the context of this challenge, a matched group is a digit $$\n\$$, followed by $$\n\$$ more matched groups. In the case of $$\n = 0\$$, that's the whole matched group.

For example, 3010200 is a valid matched group, as:

3       # 3, capturing three elements...
0      # a 0 (group 1)
1     # a 1 (group 2), capturing...
0    # a 0
2   # And a 2 (group 3), capturing...
0  # a 0
0 # and another 0.


A fully matched number is simply any valid matched group.

The list begins:

0, 10, 110, 200, 1110, 1200, 2010, 2100, 3000, 11110, 11200, 12010, 12100, 13000, 20110, 20200, 21010, 21100, 22000, 30010, 30100, 31000, 40000


(As usual, these are hand-generated :P)

Standard and rules apply.

## Testcases

(getting the 0-indexed numbers)

0 -> 0
1 -> 10
4 -> 1110
6 -> 2010
9 -> 11110
13 -> 13000
18 -> 22000
22 -> 40000


(These are based on the above list; if I've stuffed this up, it's because I stuffed those up)

# Implement Unix Timestamp to Daytime

Given an unsigned integer that represents a timestamp since 1970/01/01 00:00:00 (which is Unix epoch time), output one of these to represent the daytime in GMT timezone:

• An array that stores year, month, date, hour, minute, second.
• A string in format YYYYMMDDHHmmss.
• Or whatever similar, as long as it complies with standard i/o rules.

# Rules

• Implement the function or the full program from vanilla.
• So no built-ins nor libraries that has the fuctionality (see next section).
• Implement leap year, too; but don't leap second (although leap second is not supported).
• You just need to support up to 2038/01/19 (so input range shall be 0 to 2147483647 (inclusive)).
• Standard loopholes apply.
• Standard I/O rules apply.
• Input and output format should be consistent and not ambiguous.
• So, for example, if output is a string like 1970121000, it's unqualified, as it can be recognized as 1970/01/21 00:00:00, 1970/12/01 00:00:00, or 1970/01/02 10:00:00.
• Shortest code wins.

# Test cases

0
-> 1970/01/01 00:00:00
999999999
-> 2001/09/09 01:46:39
1145141919
-> 2006/04/15 22:58:39
1330500000
-> 2012/02/29 07:20:00
1633773293
-> 2021/10/09 09:54:53
2147483647
-> 2038/01/19 03:14:07


# Hint

Here are implementations:

# Meta

• I once posted here but it's closed.
• TODO. define what builtins are.
• The most problem is that that KSH answer has a function that directly converts to the objective string; should I prohibit it?
• Maybe I wanted to say no date objects allowed.
• Is what is so-called date object ambiguos?
• Unix Timestamp does not support leap seconds. So there is nothing to do to require someone implement leap second support for an Unix Timestamp.
– tsh
Oct 12 at 6:28
• Am I required to support year above 2038? As, you know, support only 1970~2038 would avoid some leap year issues for 2100 or 2200.
– tsh
Oct 12 at 6:31
• @tsh 1. Thank you for pointing out leap seconds. 2. I clarified to support until 2038. Oct 12 at 12:27

## Permutation of all the number which separated by ':' and ','

• Welcome to Code Golf and thanks for using the Sandbox! This is a great challenge, but as it stands it's a little unclear from the instructions what's being asked. For example it's clear from the example that 1-2,11,44:110-113 means output every permutation of 1,2,11,44 on the left column and 110,111,112,113 on the right column, but that's not explained in the instructions. Nov 12 at 20:52
• @Mayube Thanks for your comment, I've updated the instructions. Nov 12 at 22:02

# Print random characters indefinitely

Continuously print a random character (a-z, A-Z, 0-9) not separated by a newline (\n).

### Expected output

b7gFDRtgFc67h90h8H76f5dD55f7GJ6GRT86hG7TH6T7302f2f4 ...


Note: output should be randomised.

## Requirements/Rules

1. Output must be continuous (i.e. never ending),
2. Output may not comprise of newlines,
3. Output must be random,
4. Output must be only composed of characters: a-z, A-Z, 0-9.
5. No loopholes, regarding programming language version(s). Use only the tools available with that programming language, no third-party packages, modules, or other addons.

## Points

• Smallest file size (in bytes)

### Notes

Concerns: None at the moment...

• I think this would count as a duplicate of this. It's a language specific version, and indefinite, but making something loop forever isn't really the hard part of the challenge I think. Nov 29 at 0:51
• @Rɪᴋᴇʀ no, not because different. Nov 29 at 0:51
• Is "creativity" part of the scoring? If so, there's no way to objectively determine how creative something is, so you can't use that as a scoring criterion. You should probably clarify Python 3.8 is the only allowed language, or just drop that entirely (which I'd strongly recommend). Nov 29 at 0:52
• @RedwolfPrograms and Riker thank you for the tips, i'll make the suggested edits to the criterias ASAP. Nov 29 at 0:57
• Not limited to python, this might be different enough. I consider something a duplicate if the more specific challenge doesn't really encourage any different approaches than whatever worked for the previous ones, but limiting to alphanumeric and forcing an infinite stream is probably good. You should probably check if there's any other ones tagged [random] that look too similar though. Nov 29 at 0:59
• @Rɪᴋᴇʀ Understood. Thanks again! Nov 29 at 1:01
• No problem! It's an interesting challenge, and if it really hasn't been done before then I think it would be quite fun to do. Nov 29 at 1:13
• Ok! Will post this in ~22 hours... Nov 29 at 1:16
• We've had similar versions of this challenge before, and they've all been closed as a dupe of this and/or this. Personally, I would hammer this closed as a dupe of those two, as I don't think this adds anything that they don't - it's just a trivial combination of the two Nov 29 at 1:20

# Find Maximum number of 4+ letter words from Scabble Tiles

The challenge is to find the most words with 4 or more letters you can make with one set of scrabble tiles.

The tile distribution is as follows:

2 Blank Tiles
A 9  N 6    +====+===========+
B 2  O 8    | 01 | K J X Q Z |
C 2  P 2    | 02 | B C M P F |
D 4  Q 1    | 02 | H V W Y * |
E 12 R 6    | 03 | G         |
F 2  S 4    | 04 | L S U D   |
G 3  T 6    | 06 | N R T     |
H 2  U 4    | 08 | O         |
I 9  V 2    | 09 | A I       |
J 1  W 2    | 12 | E         |
K 1  X 1    +====+===========+
L 4  Y 2
M 2  Z 1


Valid words are any words that are 4+ that are available in this file, the official scrabble dictionary.

Tiles cannot be used twice. This means you can only have 1 word with a K, J, X, Q, and/or Z unless you use a blank tile to represent one of these letters.

I'm not sure how I'd do scoring on this. I want shorter code to score better, but I don't want a short piece of code that finds a lot less words to score better than a longer piece that finds many more words.

• Meh. I don't like dependency on external files; are we allowed to load it, or even embed it into the source code? Dec 17 '13 at 20:00
• as for finding more vs. shorter code, you could demand all words be found Dec 17 '13 at 20:19
• @JanDvorak Any way to use it. It's a text version of the official scrabble dictionary, it seemed to be the most fitting word list for the task. "All words being found" might be hard, considering there are probably many combinations of words that would deplete all the tiles. It's a maximum of 25 words, (25 words, 4 letters each, 100 tiles), but I don't know if it's possible to use all tiles with just 4 letter words. After so many words, you might not have enough tiles to make an actual word, which means you'd either have to go back or accept that you're not using all the tiles.
– Rob
Dec 17 '13 at 20:23
• As currently described, this is a no-input task, which means that the answer can be precomputed and then the program only needs to decompress it. Consider rewriting it to take input (either of the word list or of the tiles available). Dec 18 '13 at 8:01
• I suggest taking a list of tiles as input, loading the list of words from a predefined file and requiring all combinations / best combination to be found. Of course, if the input is the full list of tiles, the computation is going to take ages. I might allow preprocessing the word list outside the program itself (up to a certain point; a linearithmic growth?) Dec 18 '13 at 8:32
• I suggest modifying this so that input is a list of tiles, limited to a full rack or less (therefore 4-7 tiles, since our minimum word length is 4). Input should be assumed to be valid based on the standard set of tiles (e.g.: it wont' have something like 3 J's or 4 G's). This would have some practical use for a player in a scrabble game to figure out their next move (though it does not take into account tiles available to them which are already on the board).
– Iszi
Dec 18 '13 at 21:14
• Alternative mode: Input is a list of tiles, maximum 96 (so that at least 4 are remaining in the set). Output only includes words (minimum 4 letters) which can be created without those tiles. This would be interesting as it provides words that may yet be created (though, again, not taking into account usable tiles on the board) at a given point in the game.
– Iszi
Dec 18 '13 at 21:15
• Output needs to be decided as either a list of all possible words, or only the highest-scoring word(s). Another enhancement may be to require that the list be sorted descending in order of score (if output is all words), then ascending alphabetically. There's no reason to take each program's output into account for scoring. Since everyone is expected to use the same dictionary, all programs' outputs should be identical (except perhaps in sorting, if that's left out of the spec). So, this should be Code Golf.
– Iszi
Dec 18 '13 at 21:15
• It's also worth noting that, as currently written, the task could just be to filter the given dictionary down to words which have 4 or more letters. By its very nature, the Scrabble dictionary should already exclude any words that cannot be made with a Scrabble set.
– Iszi
Dec 18 '13 at 21:18
• @Iszi it's not "what are all the words you can make", it's "what are all the words you can make, where every letter used depletes a tile". There's a max of 25 words if you can use all 100 tiles.
– Rob
Dec 19 '13 at 16:40
• I think I misunderstood the problem, then. I thought it was "all the words possible using a set of tiles" not "all the words possible, using only one set of tiles". Still, my point about code golf remains. There is an absolute maximum to the number of words (each with 4 or more letters) you can make with a single Scrabble set, and a finite number of permutations which can be used to hit that maximum. Every program written with this goal should end up with the same (or nominally similar) output.
– Iszi
Dec 19 '13 at 16:56

Known Issues:

• Some rules seem a bit unclear to some users.
• Clarification may be needed on what is needed to qualify for the "win percentage" bonus.
• Win percentage bonus may not be enough to be a real incentive. (This may just depend on the language or implementation.)
• Perhaps the win percentage bonus should be eliminated entirely, or maybe it should just be made a mandatory part of the spec.
• It's been suggested to use a simple 1-9 numbering system for the board positions, instead of any sort of X,Y coordinates.
• May want to allow some flexibility on the input format. (i.e.: Input must still specify the sequence of moves thus far, using whatever addressing scheme is specified in the spec, but leave the delimiters - or lack thereof - up to the developer.)
• Exactly what is expected of the program, such as how it can figure out whose turn it is or what the output should be, seems to need some clarification.
• Some test cases should probably be added.
• Clarification may be needed on the matter of what parts of the game we can assume have followed the guide already.
• Some flaws exist in the chart. (Two already mentioned in comments on the original post.) These should be identified and addressed so that proper expectations for those conditions are clearly set.
• Original post said we would not have to account for null input (i.e.: X asking what their first move should be) but this might be a good enhancement to add.

I personally think this is a great challenge. So far, I've had a very hard time finding a lot of room for optimization and got up to probably 400 characters in PowerShell before I gave up (not even half-way through the chart yet) due to some of the above issues. I'd really like to see what some more serious golfers could do with this, once the spec is properly hammered out.

## Overview

This is the XKCD tic-tac-toe cheetsheet:

It's rather big, I know. But it's also your most valuable resource in your challenge.

## The challenge

Create a program (in your language of choice) that uses the Optimal Move Cheatsheet (henceforth OMC) to output the optimal move when given a sequence of moves.

## The input

Your program will be fed a series of moves in the following fashion:

A3 A2 B2 C2 ...


Where the first combination is always X, the second O, and so on. The letter is the Y coordinate (A-C, A at the top) and the number is the X coordinate (1-3, 1 at the left).

You may assume that the given combination is following the OMC's suggestion for each move at least for the player asking for a recommendation. You can also assume that the input will never be null (at least one move has been made). You must:

1. Figure out whether the next move is for X or O (you don't need to output this)
2. Use the OMC to decide the next move
3. Print the next move in the standard format A3

## Optional:

You may also include the player's chance of winning (as a percentage) for 50 character discount on your score.

• I think a 1-9 system would be easier than any XY system, but not by too much. The biggest issue I think is that if you go by the chart (rather than formulating your own algorithm that plays the same way) you have a ton of data to enter (there are several hundred squares in the two charts). Perhaps limit the input to only sequences starting A1 B2 (or 1 5 if you use telephone keypad numbering)? That's the center square in the X chart and the top left square in the O chart. Dec 23 '13 at 5:14
• @Blckknght Limiting the scope of the challenge makes it less interesting. Part of the challenge (if not the entire challenge) here is to find ways to shortcut the flow while still putting out accurate results. As for the 1-9 system, the simplification may be relatively trivial but it does help clear out some otherwise unneeded bloat since everyone will probably build in some conversion to a 1-9 system anyway to shorten the code. It also enables some other shortcuts where the same move suggestion applies to multiple situations which are mathematically related.
– Iszi
Dec 23 '13 at 19:47
• My point is that the chart data so dominates the code size that winning answers will pretty much have to ignore the data in the chart and use an AI. So the challenge becomes "write a Tic-Tac-Toe AI that plays exactly like this chart", which seems less interesting to me than "use (part of) this chart to make an AI with trivial code". I already have working code for the problem and bonus in about 200 non-golfed characters of Python, but it will require many 1000s of characters of data, even if I exploit some symmetries. Even if I was willing to type all that data, an AI will beat it, I'm sure. Dec 23 '13 at 20:55
• @Blckknght I'm pretty sure even a fairly straightforward implementation of the chart can be fit within about 5,000 characters - especially in a proper golfing language. IRRC, I'd finished the X portion of the chart in about 400 characters with PowerShell before I gave up on my first go at it. Even then, there was still plenty of room for optimization, and that's in a language which is far from optimal for golfing. Certainly, it's nice when you can bang out a quick answer in 15 minutes. But not every challenge has to fit in 500 characters or less.
– Iszi
Dec 23 '13 at 21:12

# Test for Irreducible Complexity (Check for Redundant Characters)

I may need some additional help coming up with the full spec for this competition. As of right now, this is just a concept.

Many interesting questions, such as the "42" question in this sandbox, involve finding the longest program which is not reducible. This means that no set of characters can be removed and still allow the program to function as desired.

The basic idea is that your program will test a Base Program to make sure that it contains no redundant characters. The input will consist of:

• Expected Output

Your program will simply evaluate all possible subsequences of the Base Program and verify that none of them give the Expected Output.

This challenge actually has a utility value to several other challenges. For example, it verifies the results of a "longest non-reducible"-type challenge. In addition, it could make sure that a golfed solution cannot be golfed further.

I assume that the winning criteria will be fastest program, as cycling through all the possibilities takes a long time.

## Problems

A sequence of length N has 2^N subsequences. Even if each evaluation is done very quickly, it might be unfeasible to test any program with more than 20 or so characters in a reasonable amount of time.

• Problem: some subsequences of legitimate answers may be pretty dangerous to the environment. You don't want to eval just everything. Dec 23 '13 at 16:59
• @JanDvorak Yes that actually is a serious problem. To what extent is it possible to fix that? Dec 23 '13 at 17:04
• Forbidding any program with dangerous subsequences? :-) Dec 23 '13 at 17:05
• A more reasonable (but very difficult) solution would be the requirement to implement a sandbox. Dec 23 '13 at 17:07
• Even without dangerous behavior, the halting problem will be an issue: it's hard to tell whether a shortened program will terminate at all, especially for every conceivable input.
– MvG
Jan 7 '14 at 23:49
• Are you sure this is possible? The problem of testing if two functions/programs/turing-complete things are equivalent is undecidable - I'm fairly sure it's reasonable easy to constract a brainfuck program that you can't tell if you can remove even a single character. May 16 at 4:44
• Extending on my previous comment - Let's assume you have a solution to this. Take a brainfuck program you want to test if halts. Let it reduce it, now you have an equivalent irreducible program. Add +. in the end of it, and then try to reduce it again. If the code never halts, that +. is reducible and when you'll run it again it will be removed. Otherwise it's important, so it will be kept. The halting problem is undecidable, therefor this is undecidable. May 16 at 4:54
• You can also get its undecidablility from that in Unary it will tell you if a given program is minimal, which is known to be undecidable as well May 16 at 5:25

# Wordlist detector

You are to write a program which, given a list of words, constructs a regular expression to match all these words but nothing else. Both your program and the constructed regular expressions are to be as short as possible.

## Input and Output

Input comes on standard input and consists of one line giving n, the total number of words, followed by n lines with one word each. The number of words will be less than 1000, the length of each word less than 30. Words will consist only of lower case ASCII letters, i.e. a-z. You may choose to ignore the first line and use EOF instead to end the list.

Output shall be written to standard output. It consists of a single line, giving a POSIX extended regular expression to match these words and no others. Since input for this regex is not restricted to letters only, elements like . or [^…] won't make too much sense, which limits the language in a natural way. You may choose whether you want to terminate the line with a newline or not. Programs may choose to print multiple lines of output, in which case only the last one will be used for scoring. So you might print intermediate results and continue searching for improvements.

## Test cases

Each submission may be accompanied by one regular expression. When scoring the submissions, I'll use this regular expression to reconstruct a word list from it. The code to do this reconstruction can be found at the end of this post. The reconstructed word list must fit the input specification above in terms of word count and length. It would be nice if your own program would be able to regenerate that regular expression from the word list, but that is not a strict requirement. But please don't paste bogus programs just to submit a challenging regular expression, though.

These test cases will be collected and fed to all programs for scoring.

## Scoring

The final score of each program will be the program size plus the size of all its generated regular expressions for the inputs collected from submitted answers, including the example from this question. So short code which produces too long results might get beaten by longer code which generates shorter expressions.

Does this still qualify as ?

Submissions which generate an incorrect regular expression for one of the test cases will be disqualified, as will those which don't terminate in the allotted time. You can use the input reconstruction program below to check whether a produced regular expression does encode the correct word list.

## Requirements

All submissions are welcome, but in order to include your submission in the tournament, it must be executable with reasonable effort on my Linux machine. It shouldn't depend on any exotic libraries, or any specialized ones which take too much work away from your own program. It must operate in reasonable time, say no more than five minutes per input. Your output must be reproducible, so if you use randomization at some point, please seed the randomizer, and please don't terminate an improove loop by a timer measuring execution time or some such.

## Tournament times

I'll run the first major tournament two weeks after posting this question. I'll include a table of the results in this question. I'll try to run tournaments repeatedly as late submissions arrive, but I'll not promise any regular schedule.

## Example

An very simple example application would be in Python 3 (53 chars):

print('|'.join(input() for i in range(int(input()))))


And here is a test case which could be posted along with the program, although this program obviously doesn't generate exactly this concise output:

bann?ana|ap(fel|ple)|s[ou]n|[hs](a|ou)nd


The expansion of that expression could be turned into the following example input, which need not be posted as part of an answer since it can be deduced from the regular expression:

10
banana
bannana
apfel
apple
son
sun
hand
hound
sand
sound


## Regex expander program

And here is a program to turn regular expressions into word lists, again written in Python 3.

#!/bin/env python3
concat = set(('',))
altin = set(('',))
altout = set()
prev = None
stack = []
regex = iter(input())
for ch in regex:
if ch == '(':
stack.append((concat, altin, altout))
altin = concat
altout = set()
prev = None
elif ch == ')':
concat.update(altout)
prev, altin, altout = stack.pop()
elif ch == '|':
altout.update(concat)
concat = altin
elif ch == '[':
ch = regex.__next__()
cls = []
while ch != ']':
if ch == '-':
crange = range(ord(cls[-1]), ord(regex.__next__()) + 1)
cls.extend(map(chr, crange))
else:
cls.append(ch)
ch = regex.__next__()
prev = concat
concat = set(w + c for w in prev for c in cls)
elif ch == '?':
concat.update(prev)
prev = None
elif ch >= 'a' and ch <= 'z':
prev = concat
concat = set(w + ch for w in prev)
else:
raise Exception("Illegal input")
if stack:
raise Exception("Unclosed group")
concat.update(altout)
words = sorted(concat)
print(len(words))
print('\n'.join(words))


This is restricted to the part of regular expression syntax which I expect for this answer. If you have good reason to use something I did not consider, feel free to do so although I will likely have to update this code to cope with it. If you find a bug, please let me know.

• This is just Meta regex golf under the constraint that the two lists between them cover all possible words. Given that some people are tackling that existing question on that basis, this would qualify for closing as a duplicate. Jan 8 '14 at 8:45

## Rhymalator

(at the point, it's just something that came to me before i wake up, so it may need some adjusting, and i'd like some feedback as to if this could be fun)

The code challenge is to write a program that takes as input a calculation in Reverse Polish Notation and outputs the result. It must at least implement + - * /. It So far so easy, but to make it fun and "artistic", the following restriction applies:

• The source code must rhyme when read. Example in PHP

$iterator = str_split($a);
foreach ($iterator as$key=>$value){ if ($key > 3){
++$virtue; } }  (the rhyme is on value-virtue) • Lines whitout readable characters count as whitespace (the two lines with } in the example) • How does that example rhyme...? – Doorknob Mod Jan 25 '14 at 12:54 • @DoorknobofSnow well, i'm not really a poet, that's why i propose it as a challenge for others :p. if you have a better example i'll replace it Jan 27 '14 at 15:58 # Implement Kalah code-golf The game of Kalah is a two-player board game in the Mancala family. Your implementation must: • Identify the active player ("Player 1" or "Player 2") • Display board state (in format specified below) • Accept input to allow that player to move (using index system below) • Announce a winner ("Player N wins") # Overview Each player has a line of six spaces, called houses, and one additional space called a store. Each space holds seeds, which move from house to house in a counter-clockwise direction. The objective is to fill your store with seeds. You must represent the board in the following two-row format with stores offset, where HH is a house and SS is a store: SS HH HH HH HH HH HH HH HH HH HH HH HH SS  The top row represents the number of seeds in player #1's spaces, and the bottom row represents the seeds in player #2's spaces. The S in each row is the respective player's store (player #1's is top-left, #2's is bottom right). Single-digit values should include a leading space. In this challenge, user-input will identify each house numerically. Use a left-to-right, indexed-from-one scheme for both sides: S 1 2 3 4 5 6 1 2 3 4 5 6 S  Note that the players' stores are not numbered, because seeds placed in the store never move out. ## Rules Wikipedia has a good summary of the game and its rules: 1. At the beginning of the game, three seeds are placed in each house. 2. Each player controls the six houses and their seeds on his/her side of the board. His/her score is the number of seeds in the store to his/her right. [Clarification: from our perspective, player 1's store is to the left, player 2's store is to the right.] 3. Players take turns sowing their seeds. On a turn, the player removes all seeds from one of the houses under his/her control. Moving counter-clockwise, the player drops one seed in each house in turn, including the player's own store but not his/her opponent's. 4. If the last sown seed lands in the player's store, the player gets an additional move. There is no limit on the number of moves a player can make in his/her turn. 5. If the last sown seed lands in an empty house owned by the player, and the opposite house contains seeds, both the last seed and the opposite seeds are captured and placed into the player's store. [Clarification: moves that end on an opponent's empty house end normally without a capture.] 6. When one player no longer has any seeds in any of his/her houses, the game ends. The other player moves all remaining seeds to his/her store, and the player with the most seeds in his/her store wins. # Example (Parenthetical text should not appear in actual output.) Player 1 0 3 3 3 3 3 3 3 3 3 3 3 3 0 > 2 (prompt arrow and line break are purely optional) Player 2 1 1 0 3 3 3 3 4 3 3 3 3 3 0 > 4 Player 2 (P2 gets a bonus turn from rule #4) 1 0 3 3 3 3 3 4 3 3 0 4 4 1 > 5 Player 1 1 0 3 3 3 4 4 4 3 3 0 0 5 2 > 4 Player 1 (P1 captures P2's seeds in space 1) 6 0 4 4 0 4 4 0 3 3 0 0 5 2 ... Player 2 12 0 0 10 0 1 0 0 0 0 0 0 1 13 > 6 Player 1 wins (because the non-finishing players gets all remaining seeds on their side, it's 23-14)  Meta question: Would this be improved by removing some of the rules? • Do the players run the game once and then take it in turns to take moves, with the process ending only when the game ends? Or do they run the program once per move? Jan 30 '14 at 10:06 [This is the first time I'm using the sandbox. I want to get feedback/suggestions before posting the question.] Make a spider web (standard, orb type) that fills frame in the ratio of n:m, where n, m are input integers. You may use the example below as a model (but you don't need to use labels). Your web should have multiple radii, at least 4 of which attach directly to the frame. The remaining radii should attach to the outer outline (perimeter) of the web. The web should have at least 15 radii. The mesh spacing should be more or less uniform spacing (although occasional weaving mistakes" or crossings are encouraged and will receive a bonus). This is code-golf, so the shortest code (minus bonuses) wins. Bonuses (to be removed from the number of characters in your code). Bonuses are awarded for the following features that reflect the architecture of an actual web (as opposed to a perfectly symmetric rendering). They are somewhat greater than usual as an incentive for attention to detail and realism. -mesh spiral instead of concentric circles: 40 pts -assymmetric web: 31 pts. (e.g. height of capture area greater than width) -irregularly spaced radii: 42 pts -distinct segments between radii (straight or crooked, but not the arc of a circle): 32 pts -outer and inner outline clearly distinct from the spiral: 41 pts -irregular outer outline: 20 pts -2 or more easily observable reverses in spiral: 40 The accept will be awarded on Feb. 20, 2014. • If there are bonuses then it isn't code-golf, by definition. It's not clear what output formats are acceptable. I'm not sure what you mean by "distinct segments between radii". "2 or more easily observable reverses" seems problematic: the ease of observing reverses is subjective, and might in addition depend on input and/or on the random numbers obtained. The weighting for the bonuses seems very arbitrary: is there any justification for it? Feb 3 '14 at 11:49 • Re: bonuses, I should probably decide on the features I want included in the web, thereby eliminating bonuses altogether. Distinct segments means that there should be 2 straight mesh segments between radius n and radius n+2 (not sure whether this should be required in instructions to be updated.) Will give reverses more thought. Feb 3 '14 at 12:02 ## Write a PHP Code Golfer code-challenge Since my currently daily programming is in PHP, I tend to try the challenges on the site using that language, but frequently I large program because of the verbosity of the language. And then I have to strip it for presentation... But this is not a tips question, it's an eviscerating challenge. The objective is to write a program in the language of your choice that takes a PHP file and outputs a golfed valid PHP file with the same functionality. The scoring will be the average reduction in percent of the result of running the program with 3 selected files (not yet selected, I was thinking of some open source library) The output file should run on at least 5.4 (so shorthand arrays, function dereference, traits are available) Since the score is the difference between the ungolfed and golfed files, techniques beyond minifying are encouraged, such as using code subtitution, eval, compression,$$(variable variables), dereferencing... Scoring example: The 3 sources have 450, 1200 and 3500 chars respectively Answer 1 results lenghts: 250, 1000, 3300 reduction: 200, 200, 200 (44%, 17%, 6%) average: 22% Answer 2 results lenghts: 350, 1050, 3150 reduction: 100, 150, 350 (22%, 13%, 10%) average: 15% In this case Answer 1 would win, even tough both answers got the same total reduction (-600 chars) • It's a specialisation of codegolf.stackexchange.com/q/3652/194 , so would likely be closed as a duplicate. Feb 4 '14 at 22:44 • @PeterTaylor I saw it. is similar, but I include an objetive goal and score. have any idea on how to make it more unique? Feb 5 '14 at 2:43 • "Making it shorter" is too broad, can I just delete some comments? If not, can I only shorten one variable and it's ok. It's not very interesting like this... Feb 5 '14 at 9:56 • @Fabinout the objective is golfing the code. If you only remove some characters, I doubt you'll get a good score Feb 5 '14 at 15:27 • Alright, the criterion is the size of the output source code. good clarification. Feb 5 '14 at 15:55 • Sum the bytes with the percents or separately? Also, no matter what sources you choose, make sure to paste the code into your questions; who knows when the code in the library will change? Feb 6 '14 at 19:11 • i'll edit the bit about scoring (with examples) tomorrow (when i come back to work). I'll post the test sources as a pastebin, but I'll wait to choose them until the question is polished enough and someone consider it interesting enough Feb 6 '14 at 19:34 • Is there anyone more with questions? is still possible that it will be marked as a duplicate? or can i choose the sources and publish it? Feb 13 '14 at 19:22 # Create diagonal code Your task is to create a program that outputs d=s*sqrt(2). Specs: • Your program must be at least 4 lines long; • d=s*sqrt(2) cannot be hardcoded as is (so using ascii, compression, encoding, etc. is allowed and encouraged); • For each line of code n, pick up the nth character. The string obtained this way must be a valid program in a programming language of your choice, that must be different from the one you used for the main program. The obtained program must compile successfully, but it can throw errors, exceptions, etc.; • If at the nth line there is no nth character, you can consider that character as a whitespace or a newline. This cannot be done for the first 4 lines, which must be long at least n non-whitespace characters. • Your main program must end successfully (no errors, exceptions, etc.); • Internet access is forbidden; • Most upvoted answer in 2 weeks wins. Happy coding! I was unsure about making this a with several bonuses (polyglot answer, secondary program still valid, etc...). ### Some bonuses for the code-challenge version: Your valid answer starts with 0 points. You gain: +10 if the secondary answer hides a third answer in it; +15 for any other hidden answer; +5 for every hidden answer that runs and ends successfully, without any problem; +10 if your main answer is a polyglot; +15 for every hidden answer that is a polyglot; Which version would you prefer? Is there something you would change/improve in this question? I personally like the one, but the KISS principle (Keep it simple, stupid!) reminds me that I may be wrong. • It's trivial to make the diagonal program be just whitespace (many scripting languages will accept this as a program) or H  (valid program in H9Q+). Feb 26 '14 at 9:26 • Nowhere does it say that the diagonal program must output your magic string: it doesn't even have to execute correctly. Your amendment doesn't really fix things: I can now have the second line be #H, the third be #HH, etc. Feb 26 '14 at 9:37 • You're right; Don't know why, on a second read I messed up the meaning of your comment. Anyway, I suppose this excludes code-challenge unless I/we don't find a way to avoid such trivial solutions. I guess popularity-contest would still be ok, since more interesting solutions could be found, right? Feb 26 '14 at 9:41 • I think my views on popularity-contest in general are well known. On further reflection, there are enough languages in which any string of bytes is a valid program that I don't think this question can work as is. If you want to save it, I think you need to look at doing something like a very difficult double-quine. Feb 26 '14 at 9:49 • Thinking about quines and diagonals (which was the "spirit" of the question), what about a sort of mini-quine? The main program would have to display d=s*sqrt(2) only, and its diagonal must reproduce the code used to display the magic string (no comments allowed). It could be tagged code-golf or code-challenge. Feb 26 '14 at 11:04 # Create a Karnaugh-map calculator Given an input of a truth table, generate a corresponding K-map. Input: Input will be of the form 10110001 where each bit is a row of a truth table. Count from the left to the right; so that input would be a table of: i2i1i0 f 0 0 0|1 0 0 1|0 0 1 0|1 0 1 1|1 1 0 0|0 1 0 1|0 1 1 0|0 1 1 1|1 Max 4 variables will be inputted K-maps (a small explanation): K-maps are a way of simplifying boolean-algebra expressions. Let's say we have 4 variables: a, b, c, d. Let the truth-table be 1110101001111111 (and the columns on the truth table be labeled, from left to right: a, b, c, d). Arrange the variables like so:  cd ab\ 00 01 11 10 00 01 11 10  Note the grey-code counting scheme. Fill in the table with the corresponding values from the truth table:  cd ab\ 00 01 11 10 00 1 1 0 1 01 1 0 0 1 11 0 1 1 1 10 1 1 1 1  Group the values in rectangles whose dimensions are the largest possible powers of two. Note that this table signifies a torus, so wrap over the left and right edges. The expression for the truth table is the ors of the and of the unchanging elements. For this, that would be: Purple group: ¬b ∧ ¬c (for 0's, make them 1 by notting the value) Green group: ¬a ∧ ¬d Black group: a ∧ d Blue group: b ∧ ¬d Expression: (¬b ∧ ¬c) ∨ (¬a ∧ ¬d) ∨ (a ∧ d) ∨ (b ∧ ¬d) Output: • Generate a 2D K-map (for more variables, add on either side) and show the grouping. K-map must be of the form I used. For less variables, remove rows or columns and change the list on the top left corner. • assume alphabetical ordering on the variables, that is, the first variable is a, second: b, third: c, and so on. • Also show the expression. Rather than use the unicode characters, the following is permissible: ~ instead of ¬ * instead of ∧ + instead of ∨  Edit: Possible duplicate: More fun with gates: Karnaugh simplification • I think the grouping is not unique and therefore I might choose the most basic grouping (i.e. none). Feb 26 '14 at 9:02 • Although @Howard's concern is partially answered by "rectangles whose dimensions are the largest possible powers of two", it's not obvious to me why you haven't also circled the entire row 10 and the bottom-right quadrant. Feb 26 '14 at 9:29 • @PeterTaylor You're right - didn't read that line. But still my main concern is correct: it is not unique. Or as your remark shows it is not optimal if you choose all rectangles. Feb 26 '14 at 9:33 • Also for higher number of variables you have to either go to n dimensional K-maps or you won't find all possible rectangles (they are no longer adjacent in the matrix). Feb 26 '14 at 9:38 • @PeterTaylor In priority: Biggest rectangles, then least number. That is a big rectangle, but it is redundant with the others because every 1 in it is already circled. Feb 26 '14 at 16:44 • @Howard Good point. I'll restrict it to 4 or less variables. Feb 26 '14 at 16:47 • For the expression: rather than using A and V, why not * and +? That's fairly conventional use of field notation to represent GF(2). Feb 26 '14 at 17:11 • Ahem. OR is, of course, not the same as + in GF(2). But * and + is still the conventional notation for operations over the Boolean semiring. Feb 28 '14 at 15:31 Title: Implement ROT-13... in ROT-13 Content: Challenge: Implement ROT-13 in code that works as both itself and as the ROT-13 version of itself. ### Scoring: Your score is calculated as a percentage of used, ROT-13 eligible bytes in total of both versions of the program divided by total bytes (all characters) of both versions. A used, ROT-13 eligible byte is any character that is not part of a comment or ignored by the compiler/interpreter. For example, any character in a brainfuck program that is not +-<>[],.  is not considered a used byte, and any character in a C program including and after // or inside /* */ is not considered a used byte. All special symbols in APL are not considered used, as are all characters in a Whitespace program (sorry). Example scoring: ### C: 21/32 = 65.625% main(){printf("Hello World!");}  • Originally this question was ROT-47, not ROT-13. The rules are chosen so that choice of language doesn't easily determine the winner; otherwise, whitespace would easily win. When I changed it to ROT-13 I made only [A-Za-z] count so that a language like golfscript or brainfuck would not automatically score 100%. Looking for thoughts on how to capture the idea without making it too "choice of language" dependent. Mar 3 '14 at 21:13 • Just saying, I have a C answer for the 47-version: qp.mniip.com/p/tz pick either of the lines Mar 3 '14 at 21:29 • @mniip Okay I undeleted it :) Mar 3 '14 at 21:48 # Convert input to ASCII Semaphore With monitor resolutions getting higher and font sizes getting lower, a good programmer has to make efforts to ensure that output is accessible to the visually impaired. This can be problematic when the only display is in text. Toward this end, your assignment (if you choose to accept it) is to write a program that converts text input into ASCII art flag semaphore. ## Input 1. Your program must accept any letter in the ASCII character set from A to Z (case insensitive) and spaces. 2. The program can accept input in any way that is convenient for the language it is written in (stdin, command line, file, etc.). ## Output 1. The program should output an ASCII art representation of the input string in flag semaphore. Follow this link to see the expected encoding. 2. Line feeds and carriage returns should be interpreted as spaces. 3. Numbers and other non-letters in the input may be ignored. 4. You may use whatever ASCII art representation of the semaphore sender you like, but it must contain a person holding two flags and have distinct arms, legs, head, and flags. It must be at least 10x10 characters. 5. Output may be either horizontal or vertical. ## Example Input: Hello Output:  ### ### # _____######## | | ### |__| #### # ### # ### / # # /\ # # / \ # # \ / # # \/ ## ## /\ / \ /\ / # \/ ### # ### # # # #### # ### # ### # ### # ### | # # |__ # | |# |__|# ## ## /\ / \ /\ / # \/ ### # ### # # # ### #### # ### # ### # ### / # # /\ # # / \ # # \ / # # \/ ## ## /\ / \ /\ / # \/ ### # ### # # # ### #### # ### # ### # ### / # # /\ # # / \ # # \ / # # \/ ## ## /\ / \ \ /\ \/ # # ### # ### # # _____######## | | ### |__| ### ### ### # # # # # # # # ## ##  ## Scoring This is code golf. Shortest code wins. • define "easily recognisable". Would a simple 3x3 compass (say, with a head if not covered) do? say:.o. -|. /|. ; or even: ... xx. x.. (read by lines, dots represent spaces) Mar 6 '14 at 20:16 • @JanDvorak Good catch. Edited to include distinct items that must be present and a minimum size. I'm not exactly sure how to make that rule more clear. Mar 6 '14 at 20:34 • Define "person holding two flags". Is what I drew a person? Is this a (lying, due to formatting issues) person: o--? Are three x's on a vertical line a person? Mar 6 '14 at 20:43 • @JanDvorak Ack! had to many tabs open and forgot to save my edit. I think number 4 for output should cover that. Mar 6 '14 at 20:47 • Define "distinct arms, legs, head, and flags." But I suggest allowing very small figures as well, otherwise this will turn into a kolmogorov-complexity-like question with very little of the code actually involving generating a pair of directions. Mar 6 '14 at 20:51 • Very similar to this question. The ascii art is more complex here so perhaps it's not close enough to be called a duplicate... Mar 6 '14 at 22:20 • I disagree with @JanDvorak: I think this would be better with a fixed output spec which must be followed exactly. That way people can golf their code rather than the output. Mar 6 '14 at 23:59 • Standard figures seem best to me as well. If you demonstrate a full "clock" of hand positions for the standard figure, then you can require those as output. That's easier to assess than free reign for variations. Mar 7 '14 at 0:14 With its strange choice of 9 different characters (plus space and newline), the ASCII art version of the FreeBSD logo has always looked to me as if it might be nicely formatted, obfuscated code is some programming language. (Is it?)    s .....---.......--. -/ +o .-- /y: +. yo:. :o +- y/ -/ -o/ .- ::/sy+:. / -- / : : : : / / .- -. -- -. : : .-- --. .---.....----.  Therefore I would like to challenge you to make it one: Either specify minimal changes to an existing programming language or minimal changes to this piece of ASCII art (making the artwork look different or significantly changing the character set used are definitely major changes), so that the logo, as source code generates meaningful output. This should be a challenge, although I wouldn't mind some way of introducing hard scoring and run this as . ## King of the Hill Fighting In this game, a player controls 5 bots that attack the other players 5 bots. Each bot has life points, and has to reduce the other playres lifepoints to zero. This post is program that tests the controllers. It is in literate haskell. > import Data.Set as S > import Data.Map as M  Here is the arena:  D---G /| |\ B | | J /|\| |/|\ A | E---H | L \|/| |\|/ C | | K \| |/ F---I 20 12 4 16 8 0  Positions are denoted by letters > data Positions = A | B | C | D | E | F | G | H | I | J | K | L deriving (Show, Read, Eq, Ord)  Each player is presented a map in which their side is the one with A. Here is code that will reflect it so each player sees their own view. > pairFlip = (\(x, y)->[(x,y), (y,x)]) > reflect = M.fromList$ [(A,L), (B,J), (D,G), (C, K), (E, H), (F, I)] >>= pairFlip


Lines denote connections.

> connections=S.fromList $> [(A,B), (A,C), (B,D), (C, F), (E, D), (E, F), (D, G), (E, H), (F, I)] > >>= pairFlip > >>= (\(x,y)->[(x,y), (reflect ! x, reflect ! y)]) > > connected x y=(x, y) S.member connections  The numbers below are the number of life points of generation that each bot. > regen = M.fromList$
>   [ (A, 20), (B, 16), (C, 16), (D, 12), (E, 12), (F, 12)
>   , (G, 8), (H, 8), (I, 8), (J, 4), (K, 4), (L, 0)]

• Is there supposed to be a specification hidden in here somewhere? Mar 14 '14 at 16:30
• @Peter Taylor Just not done yet. Mar 14 '14 at 16:44
• You won't get lots of answers if it's limited to Haskell. Mar 14 '14 at 17:57
• No no no, the above post is also a program for testing it. I will add in code that can take arbitrary programs and use them. Mar 14 '14 at 21:17

# Create the perfect CSS reset stylesheet

Your job is to create a CSS reset stylesheet, That is, a stylesheet that you can apply to any HTML file, and the result will look the same in all webbrowsers. Because we all know that cross-browser interoperability is very important these days, and you want to make your website look pixel perfect everywhere.

The rules:

1. You must be able to throw any valid HTML5 document at it and the result will look the same in the main browsers.
For simplicity, you can assume that the HTML document does not contain any styles of its own or Javascript that changes anything. Just pure, static HTML that is valid HTML5.
2. The main browsers are Firefox >= 22, Chrome >= 28 and IE >= 10.
3. To avoid solutions like *{display:none} (which do indeed make all documents look the same in all browsers, yes) the result must be identical to the document without the stylesheet in one of the browsers.
In other words, take your browser of choice and make the document look like that in the other browsers.

The winner is the stylesheet that works the best, again, on any HTML file that is valid HTML5 and uses no other styles. I'm not looking at efficiency. If you come up with a 100K stylesheet or one that slows the site down considerably, that doesn't matter, as long as the end result looks good.

That's the question so far. Now I have a bit of a problem with "any HTML5 document"; I know I could provide a test document that people can work with, but then you'll get answers that cater to only that particular test case, and that's not what I want. Not sure how to handle this. Ideas?
Also, I want to include Safari as a main browsers, but as I don't have a Mac, I can't test the results on it. Not sure how to handle that.

• Mar 14 '14 at 12:59
• @PeterTaylor That breaks rule #3. Mar 14 '14 at 13:05
• The result must be identical to the document without the stylesheet in one of the browsers. I assume you have loaded a webpage without a stylesheet before? If you mean that it can have the main stylesheets, and we just need to create a modification stylesheet, you should specify that.
– user10766
Mar 14 '14 at 16:17
• @hosch250 What I mean is that I want the document to retain its basic HTML-ness, so it shouldn't look like plain text. Take this fiddle for example; open it in all browsers, and then add CSS to it so that it looks like (your favourite browser) in all other browsers. If the name of such is "modification stylesheet" rather than "reset stylesheet", I apologise. Mar 14 '14 at 19:32
• OK, I was thinking about how most HTML pages rely on CSS stylesheets to even be legible. If you took the CSS sheet off any webpage, it would not look the same; in fact, if the HTML wasn't laid out good using accessibility techniques, it wouldn't be legible.
– user10766
Mar 14 '14 at 20:01
• Pixel perfect isn't going to happen because of issues around anti-aliasing: CSS doesn't let you do things like enable ClearType on Safari/OS X or disable it on IE/Win. So the best anyone can do is somehow obtain the default stylesheets for the listed browsers (e.g. iecss.com but updated) and then find a minimal diff. Mar 14 '14 at 20:09
• Guys, I'm not interested in solutions to the question right now. I want to know if the question is OK! Specifically if I can get away with not posting a testcase like the fiddle above. Mar 14 '14 at 20:38

# music theory challenge

Create a program that takes some input in the form of frequency, waveform, and duration that generates an audio stream based on the input.

You can take input parameters however you choose, but if I input (translated to your method) 440Hz, sin(x), 3 seconds, your program should play or create a file for a sound 3 seconds long at 440 hertz on a sine wave.

Also, any output should be musically correct as far as frequency is concerned. See http://www.phy.mtu.edu/~suits/notefreqs.html for example frequencies

Since this is a popularity contest, the rest is up to you. I bid you Good programming!

Oh, and any use of external functions or APIs is ok, as long as they weren't developed specifically for this contest.

• If the program takes "input in the form of frequency, waveform and duration" then where do linear functions fit? What do you mean "output should be musically correct as far as frequency is concerned" given that the input is frequency? Is it supposed to correct the input: "You said 494Hz but you must mean 493.88Hz"? And simple synth has been done before in various guises: see music. To differentiate this and make it non-trivial you could perhaps specify a set of basic synth operations which need to be configurable (e.g. input specifies generators, envelopes, filters, mixers). Mar 14 '14 at 8:39
• On second thoughts, that would probably work better as a Code Review Code Challenge Mar 14 '14 at 9:23
• @PeterTaylor I didn't even know about Code Review Code Challenges <intrigued>. Linear isn't the right word...and I think that statement is redundant anyway, so I'll nix it. Mar 14 '14 at 12:44
• Actually, I'm going to re-write this challenge...I don't know yet whether it'll be here of on CR Mar 14 '14 at 13:07

## Calculate pi using a unique method

Your task is to calculate or approximate pi using the most interesting method you know. Well-known things such as using inverse trig functions (asin, acos, atan) or commonly used convergent series are considered uninteresting.

You may calculate pi to any precision desired, but the more precision you can achieve, the better.

• I couldn't find an exact duplicate of this, but I'd like to know if this overlaps too strongly with an existing question. Mar 14 '14 at 18:51
• If you rule out convergent series, what's left? Mar 14 '14 at 20:02
• @PeterTaylor If someone knows of a convergent series that isn't on Wikipedia, that would make a good answer. I know of an answer that does not use trigonometry or an approximation, but calculates the digits directly. Mar 14 '14 at 20:08
• Is it in mathworld.wolfram.com/PiFormulas.html ? I've got some ancient code which uses a spigot hypergeometric evaluator to compute pi as 3*F(1/2, 1, 1, 8/5 ; 3/5, 4/3, 5/3 | 2/27), but I would expect that to count as well-known. Mar 14 '14 at 20:11
• @PeterTaylor I'm familiar with it in layman's terms only, but I don't see it there. It could be related to some of them, but I don't see more than a small resemblance. It isn't original with me, BTW. Mar 14 '14 at 20:22

# I like trees

...so this is a challenge to make me a tree.

Produce a program called tree which takes a single integer argument, N and draws a randomly-generated tree N levels deep, where level 0 is just the trunk.

• Your program must produce visibly different results for at least N=0..5
• The tree ought to not be symmetrical in any axis.
• The tree should be an image
• Tree(5) should mostly fill dimensions of at least 200w*250h
• I should be able to run your tree from a bash prompt, eg. '\$ python tree.py 3'

I also accept ferns.

Optionally your tree may be 3d, iterate forever, be colourful, have leaves at level 5, or be lit according to the time of day. However, this is code-golf, so the smallest file wins.

Tags: code-golf

# Implement multi-line lambdas in Python.

Guido van Rossum said it couldn't be done, prove him wrong. Your solution should allow multi-line anonymous functions, like:

>>> f = multilinelamba("hour", """
...     if hour > 20 or hour < 6:
...         print "Good night"
...     else:
...         print "Hello world"
...     """)
>>> f(10)
... 'Hello world'


Your solution should be as close as possible to the behavior of real def or lambda. The actual syntax doesn't matter. E.g. you may choose to pass the code as a string as above, or you may find a way to avoid it. The implementation is also open, you may for example define a function, write a preprocessor, or edit the python source, but keep in mind that the solution should fit in the answer, so the last option probably won't work.

Your solution must allow arbitrary python code inside, except the following which is optional:

• recursive use of the multilinelambda "statement" inside of the multilinelambda
• calling the function recursively, i.e. using f inside the multilinelambda in the above function
• defining classes and
• importing modules (these two might be too hard)

You must also be able to use a multilinelambda as a parameter when calling a function.

You get bonus points:

• If your solution captures outside variables in a closure, like real def does
• For correct handling of exceptions in the multilinelambda. They should display similarly to when using def, and include line number relative to the file.
• For allowing default parameters
• For allowing *args and **kwargs
• If the solution admits any kind of consistent indentation. Two options must be considered:

• All lines have a common indentation (like in the example above) that can be stipped away.
• The first line of the body is given on the same line as the multilinelambda statement. In this case, all the remaining lines must be checked for consistency. It makes a difference whether the first line starts a block or not. Example:

multilinelambda("x", """print "Hello"
print "World" """)

multilinelambda("x, y", """if x > y:
print "case 1"
else:
print "case 2"
""")


In both cases, I may add or remove the same number of spaces to/from each of the lines following multilinelambda.

Any ideas for additional criteria? I personally don't really care much about picking a winner, this is more about tinkering and proving that it can be done. But in any way, more "unit tests" will only benefit the question.

Foreword: This might have been done before, but I couldn't find any such cases. I think the scoring is quite fair now, and the challenge quite clear, but any criticism is welcome. Only thing I am not sure of (besides maybe a similar question existing) is whether it is rewarding enough to add a single language or whether a 2 byte solution which just runs in two languages is going to win (is that possible?).

# The challenge

Write a single piece of code that will only output different deterministic integers depending on the language it has been interpreted as.

# Scoring

Length of the code divided by the multiplication of the score of every used language. Esoteric languages have score 2 and production languages have score 3. For example, if you have a code of length 120 which runs in whitespace and javascript this will give a score of 120/(2*3)=20.

# Rules

• Versions and forks: Different versions and forks may count as different languages, provided that the output is not determined by the version or similar constants in any way. In other words: <?=intval(phpversion())?> or 1<!--[if IE 8]>1<![endif]--> is not allowed.
• The outputted integer should be the constant and only dependent on the language it is run in.
• Only the most common compiler for a language should be used.
• The code should output nothing besides the integer.
• No two interpretations (languages) of the code may yield the same integer.
• In cases where there is any serious discussions of a language being esoteric, it will be counted as esoteric if no commercial company with at least 50 employees can be pointed to developing it's main product in the discussed language.

^ Blame the sandbox for that last crazy over specific rule

• Define "esoteric." Also, the last time is fairly opinion-based. And what about different versions of the same language? Or similar languages (i.e. C and C++)?
– Doorknob Mod
Mar 22 '14 at 21:40
• Yes, a two-byte solution which runs in two languages is arguably possible. The arguments will come around things like what precisely you mean by "output ... [an] integer". Is additional non-numeric output (punctuation, ans - , or the like) permitted? If so, can the integer be part of an error message from the interpreter? Also expect arguments about whether languages are esoteric or production: it's clear-cut for C and Piet, but there are plenty of languages in much greyer territory. Mar 22 '14 at 23:30
• @Doorknob: Added a link and a rule regarding esoteric. Addressed the issue regarding forks and versions. Mar 23 '14 at 0:27
• @PeterTaylor: Great point regarding additional output! Would you have an example of a language you would consider to be gray? I added an additional note regarding the esoterism, but would like to have a 'gray' language to see whether the added rule would make a clear cut or still keep it gray. Mar 23 '14 at 0:29
• "Major/generally known" is highly opinion-based...
– Doorknob Mod
Mar 23 '14 at 0:31
• @Doorknob: Although programmers do tend to think that anything a computer can not parse is opinion based, it is not hard to draw a line there knowing any of the social sciences, but fair enough, let me change that to a something even a programmer is able to comprehend. Mar 23 '14 at 0:38
• Okay, seriously, now you're just being ridiculous. The reason an objective specification is needed is because two people might disagree with the interpretation of the rule.
– Doorknob Mod
Mar 23 '14 at 0:45
• The grey area I was thinking about is mainly functional languages. Common LISP, Haskell, OCAML, and F# all see some serious use; I'm not sure whether any of them meet your updated criterion. I can also report that a two-byte solution which runs in two languages is possible, but wouldn't win: I've found a three-byte solution which runs in three languages. Mar 23 '14 at 18:10
• J and K were designed as production languages, but I haven't seen anyone use them as such. What do they count in this chalenge? Mar 24 '14 at 16:16
• "it will be counted as esoteric if no commercial company with at least 50 employees can be pointed to developing it's main product in the discussed language." - first off, I don't think this kind of data is readily available. Second, I doubt you'll find a company that still codes in Algol, Perl or Fortran. Apr 4 '14 at 7:46

# Split string of powers of 2

I had this idea while playing 2048; Every single power of 2 is unique, even if it contains another power of 2 as a substring because there are none that consist entirely of powers of 2.

For example, the string "2048409632864" can be split into 2048, 4096, 32, 8, 64 easily enough, but it can also be split into 2, 0, 4, 8, 4, 0963, 2, 8, 6, 4` with a simple left-to-right algorithm, which is incorrect.

So, the challenge is to correctly split these numbers in the shortest byte count possible. Is this a good idea?

• But 128 can be split into 1 (20), 2 (21) and 8 (2**3) ... Mar 24 '14 at 15:13
• Related - and read the comments, because I think a lot of that discussion is relevant to this question. Mar 24 '14 at 15:53
• Does the program need to split the string into the smallest range possible? So if you get 2048, do you need go back and convert it into 2, 0, 4, 8?
– user10766
Mar 24 '14 at 15:53
• also, that no word in a language can be decomposed does not imply that concatenations of words in that language are always unique. Mar 24 '14 at 16:13