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


To post to the sandbox, scroll to the bottom of this page and click "Answer This Question". Click "OK" when it asks if you really want to add another answer.

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.


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
  • Comments addressing specific points mentioned in the proposal
  • 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 requires more feedback, but it's been ignored, you can ask for feedback in The Nineteenth Byte. It's not only allowed, but highly recommended! Be patient and try not to nag people though, you might have to ask multiple times.

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.


Search the sandbox / Browse your pending proposals

The sandbox works best if you sort posts by active.

To add an inline tag to a proposal, use shortcut link syntax with a prefix: [tag:king-of-the-hill]. To search for posts with a certain tag, include the name in quotes: "king-of-the-hill".

  • \$\begingroup\$ What if I posted on the sandbox a long time ago and get no response? \$\endgroup\$
    – None1
    May 15 at 14:05

4691 Answers 4691

94 95
97 98

Would someone like to write a crontab puzzle?

I have just asked for a software that displays all times at which a cronjob runs. As I think more about it, this might be a nice golfing question.

Unfortunately I'm not too familiar with the crontab specification, especially when it comes to combining operators such as

*/15,34,49-52 * * * * /path/to/command

Is that suitable for code-golf at all? If someone or a group of people would define it as a puzzle, I'd be glad to see it.

Starting point:

The program

  • takes a crontab line as input
  • checks if it is valid or not
  • if valid, from now on lists the next execution times
  • limited to a user definable amount


program -n 10 30 17 * * *

produces 10 lines of output (assuming today is 2015-10-22 18:00)

2015-10-23 17:30
2015-10-24 17:30
2015-10-25 17:30
2015-10-26 17:30
2015-10-27 17:30
2015-10-28 17:30
2015-10-29 17:30
2015-10-30 17:30
2015-10-31 17:30
2015-11-01 17:30

Word Game KotH

First of all, I don't know what this game is called (or if it even has a name), but it's a modification of a game I've played a few times on road trips, especially with my family. I'll be thinking of a better name.

Any suggestions at all are very welcome.

How It's Played

There are 51 bots playing per game. At the beginning of the game, they are given a collection of letters (which is not necessarily a word), for example "a" or "jet." The bots take turns in a predetermined order. When it is a bot's turn it is passed the current word(s) and has four2 options:

  1. It can change a single letter to any other letter.
  2. It can add a single letter to any position in the word.
  3. It can swap any two letters in the word.
  4. It can split the word at any point.

If you didn't infer already, these actions are allowed with the caveat that their result is a valid word or two valid words, if the bot chooses to split. The game ends when the combined lengths of all the words in play are 3 times the length of the longest word in the dictionary used (e.g. if "onomatopoeia" is the longest word, the max length would be 36 letters since it has 12) or when only one bot remains. The bots are scored on how many turns they last*, and the winner of the game is granted a bonus3.

*The turn they lose on is not counted, so if the bot were to lose on its first turn it would have lasted 0 turns.

A word is valid if it is both in the dictionary and hasn't been played before.

Bots should take a reasonable amount of time in making their plays (no more than a few seconds).

Available Methods

isValid(word) returns a Boolean value (whether the word is valid or not).

getDictionary() returns the entire dictionary as a single string.

getPreviousPlays() returns the words previously played as an array (one word per element).

Once any of the following methods are called, the bot's turn is over:

change(index,letter) changes the letter at that index to the letter provided. This method cannot change a space to a letter (to prevent stalling).

insert(index,letter) inserts the provided letter at the provided index.

swap(index1,index2) swaps the letters at index1 and index2.

split(index) splits the word into two by inserting a space at the specified index. Both of these words have to be valid4

If any of the calls to these methods are invalid, the bot is disqualified for that game (treated as a loss).

Author's notes

  1. Basically a random number I determined; I don't know if it's too big or small.
  2. Is four too few to make this challenge interesting?
  3. This bonus is undetermined as of now, but I'd say 2 points tentatively. I'm also a bit unsure as to whether that is a good scoring method. Should it just be on victories or position in victory (i.e. first, second, third, etc. place)? I'm also worried that this might encourage users to submit bots that collaborate to last as many rounds as possible.
  4. Would it be more interesting if this ignored validity? e.g. if you have candies dog as the two words, splitting candies into can and dies would be valid even if either of those words had been played before.

I haven't done a KotH submission before, so I'd love feedback as to how to improve this.

Unimplemented Portions


This is the big unimplemented portion: I want to get feedback on the idea as a whole before diving into programming out a controller.


I'm still unsure as to how the games should be scored.

  • \$\begingroup\$ I don't understand how the game starts. If I'm passed a bunch of random letters, surely the majority of the time I can't make a word and I lose immediately? \$\endgroup\$ Oct 24, 2015 at 8:58

Create CHIQRSX9+ Analogue Program.

Your task is to create a program in same language, that when given a CHIQRSX9+ will print a that analogue. That analogue program will do similiar thing that CHIQRSX9+ program do. There's exception though. There's may be more than 1 instruction. Then it's meant to be executed

  1. C => Read until empty line and print all entered lines, including empty line.
  2. H => Print "Hello, world!"
  3. I => Read input until a newline then return that analogue
  4. Q => Print the analogue program source code. (Not the entered one)
  5. R => Read input until a newline then print that string after doing ROT-13
  6. S => Read comma separated number until newline and sort that.
  7. X => For this, X have undefined behavior.
  8. 9 => Print 99 Bottles of beer with correct pluralization.
  9. + => Increment Accumulator.

Printing instruction(C, H, I, Q, R, S, and 9) begin in a new line. After everything is printed, accumulator count is written at new line. Final newline is optional.


If there's program X written in Haskell, then

>main=interact$(++"\nHello, world!\n0").unlines.takeWhile(/="").lines

Which when compiled (Example as W) will do that

This is a line
This is another line

>This is a line
>This is another line
>Hello, world!

Another example for Q

>main=putStr(s++[';','s','=']++show s);s="main=putStr(s++[';','s','=']++show s)"

Yet another example

>main=printStr"Hello, world!\n1"

Here is for indication of output. DO NOT print it.

Sandboxing Question

How about scoring. I want to reward short produced program. However, shorness of producing program is also counted. I guess just 10A+5B+C. Where A is length of original source code, B is length of "QQQQ" analogue program. C is length of "CHIQRS9+".

  • \$\begingroup\$ Well, please tell me what's wrong in my question? \$\endgroup\$
    – Xwtek
    Oct 24, 2015 at 15:51
  • \$\begingroup\$ 1. I think this is a source-source compiler, which might be a more recognisable title than "create analogue program". 2. The HQ9+ family has a very mixed reception here, so you should probably expect some downvotes. 3. Why does the scoring system include a weight for votes? \$\endgroup\$ Oct 25, 2015 at 7:43
  • \$\begingroup\$ 1. If it source-source compiler, Q will compiled to main=putstr"Q\n0" instead. \$\endgroup\$
    – Xwtek
    Oct 25, 2015 at 13:10
  • \$\begingroup\$ 2. What's wrong about HQ9+ except that it can be used to cheat at golfing. \$\endgroup\$
    – Xwtek
    Oct 25, 2015 at 13:11
  • \$\begingroup\$ 3. Just a tiny boost since "QQQQ" "CHIQRS9+" and original source code is already very big. Wait I'm writing it wrong. It must be subtraction. Else it will be penalty \$\endgroup\$
    – Xwtek
    Oct 25, 2015 at 13:12
  • \$\begingroup\$ Is that vote annoying? \$\endgroup\$
    – Xwtek
    Oct 26, 2015 at 8:05
  • \$\begingroup\$ Congrats on posting the 1600th answer in the Sandbox! \$\endgroup\$
    – mbomb007
    Oct 27, 2015 at 15:57


The goal is to stitch several ordered lists of numbers into a single list that contains each of those lists as a contiguous sublist, with the numbers in the same order without gaps. The resulting list should be as short as possible.


n ordered lists of numbers between -2^63 and 2^63-1


A minimum-length list so that each input list appears within that list with its elements in the same order without gaps



[1, 2, 3] [3, -38, 23424, 292] [0, 1, 2] [-38]


[0, 1, 2, 3, -38, 23424, 292]

The output contains each of the input lists:

[0, 1, 2, 3, -38, 23424, 292]
   [1, 2, 3]
         [3, -38, 23424, 292]
[0, 1, 2]
  • \$\begingroup\$ Many languages have built-ins both for flattening a list of lists and for removing duplicates, giving them a straightforward solution. I think that makes this too easy overall. The removing duplicates part is like this challenge, though it uses characters and requires preserving order. \$\endgroup\$
    – xnor
    Oct 30, 2015 at 21:26
  • \$\begingroup\$ But it is not only about removing duplicates, but also about finding the perfect combination of lists, so you have to figure out in which order you want to put the input lists together. Also it might be necessary to have duplicates in the output to be able to have all input lists in there. \$\endgroup\$
    – Nitek
    Oct 31, 2015 at 7:13
  • 2
    \$\begingroup\$ Oh, my mistake, I didn't realize the lists had to appear as contiguous subsequences. Let me edit that to try to make it clearer. \$\endgroup\$
    – xnor
    Oct 31, 2015 at 7:18
  • 1
    \$\begingroup\$ Out of curiosity, I found notes about this as an algorithmic problem, and it's NP-hard, so solutions are going to be exponential time. It would do good to include some test cases that a greedy algorithm would get wrong. \$\endgroup\$
    – xnor
    Oct 31, 2015 at 7:29
  • 2
    \$\begingroup\$ Looks like we already have this challenge. \$\endgroup\$
    – xnor
    Oct 31, 2015 at 8:53
  • \$\begingroup\$ Good catch. It's indeed the same problem. Thanks for pointing that out! \$\endgroup\$
    – Nitek
    Oct 31, 2015 at 9:03

Hello, World! Fitted in cases.

Your task is to take a line of input and print Hello,world! multiple times fitted to length of input. The cases of that character is fitted to input in same position(except shifted from deletion). If the corresponding character is non-alphabeth, you must use default case(lowercase except for "h" that is uppercase). And for punctuations, if the corresponding character is not punctuation, it will deleted. And if the corresponding character is space, the the ouput is space but it doesn't skip the "Hello,world" writing.


Hello, world!
Hello, world!

About punctuation deletion and space insertion

I have a dog. I name it Underdog.
H ello w orld H ello wo Rldhellow



Other examples





Example Program

Here is ungolfed version of example program in Python. If there is error, correct me.

h="Hello, world"
for a in xrange(len(p)):
    if p[a]==" ":
        k=k+" "
    if isUpper(p[a]):
        if isAlpha(h[i]):
    if isLower(p[a]):
        if isAlpha(h[i]):

Sandbox Question

This language is surely need to be fixed.


How am I doing?

My boss is a flashy sort of fellow. He likes all things animated.

He's asked me to write a progress bar to show the completeness of our super-secret project.

Now with me being me, I'm getting you to write this for me and showing the best one to my boss.


  • Output a progress bar to stdout.
  • Whenever a newline is sent to stdin, increase the percentage on the percentage bar by 1%
  • If not already enabled and if possible in your language, set the terminal mode to non-echoing (stdin doesn't automatically get shown, think like when your typing in your password for sudo)
  • You may not assume the cursor is in a certain position, it must produce a progress bar relative to where you started the program (no absolute jumps)

To help you, you may use ANSI escape codes, ANSI colour codes and any UTF-32 unicode points.

The winner is the entry with the most upvotes.

Sandbox Notes:

  • Is this too broad? - I'm sticking to ANSI only but I'm not saying anything else about what it looks like.
  • \$\begingroup\$ Anyone care to say why this is worth a downvote? \$\endgroup\$
    – Blue
    Nov 2, 2015 at 17:12
  • \$\begingroup\$ Popularity contests tend to attract them (even the good ones). \$\endgroup\$ Nov 3, 2015 at 19:47
  • \$\begingroup\$ This doesn't seem very tightly defined. Generally, the broader a popularity contest is, the more I expect it to gather downvotes. \$\endgroup\$ Nov 3, 2015 at 19:48
  • \$\begingroup\$ Also, a simple requirement means most of the popularity of an answer will come from optional extras rather than meeting the spec. See the line between art and programming for other's thoughts on this. \$\endgroup\$ Nov 3, 2015 at 19:50
  • \$\begingroup\$ Thanks for the link, I think I'll just let this question die here (I'm not sure if I should delete it or not, I'm going with not deleting it unless someone else says otherwise) \$\endgroup\$
    – Blue
    Nov 3, 2015 at 19:57
  • \$\begingroup\$ I usually delete my challenges once I know for certain I will not post them, but for ones I (or someone else) might be able to salvage in future I leave them around. \$\endgroup\$ Nov 3, 2015 at 19:59
  • \$\begingroup\$ I don't think this one is ready for main, but remember that here (as on main) a lone downvote doesn't really mean anything. It could be anyone for any reason - rational or otherwise. \$\endgroup\$ Nov 3, 2015 at 20:00

Kaprekar Transformation

Kaprekar Transformation is an transformation a number by following that instruction:

  1. Take n-digit integer.
  2. Sort it anscending and descending.
  3. Subtract the largest number and smallest number.

Your program have to do this:

  1. Take 1 number, x.

  2. Output all possible cycle and fixnums for doing repeated x-digit Kaprekar Transformation on all possible input. Rotation is considered same. So it is invalid to print:


The output is a list consisting of list representing the cycle. You may using any style of list and even intermix it with restriction that it should not be ambigous. For example, comma separated item with item using comma separated item with enclosing bracket is OK, but not comma separated item with item using comma separated item without enclosing bracket.




  • \$\begingroup\$ I'm afraid this is a duplicate: codegolf.stackexchange.com/q/2762/8478 ... also, for future reference, requiring one specific list format is bound to put an arbitrary set of languages at a massive advantage (those which can just use their native string format), while all others may have to do some non-trivial string processing which distracts from the (interesting) core of the challenge. \$\endgroup\$ Nov 2, 2015 at 12:56
  • \$\begingroup\$ @MartinBüttner No, it is the generalization. You have to handle arbitrary digit this time. And you have to detect cycle and find all cycle given a digit. Btw, there is typo. 2 39 is different example. \$\endgroup\$
    – Xwtek
    Nov 2, 2015 at 13:04
  • \$\begingroup\$ Task one seems to be identical. The fact that the other challenge only has to work with 4-digit numbers doesn't seem substantial. I'm pretty sure almost any answer there can be adapted to a variable number of digits in a couple of bytes. As for Task 2, I did overlook that. You could simply reduce the challenge to just task 2 (I'm not even sure why you'd combine two independent tasks into a single challenge?). Even task 2 can be solved by simply looping the solution to task 1 over all possible X-digit numbers, but there might be other ways to golf this one. \$\endgroup\$ Nov 2, 2015 at 13:07
  • \$\begingroup\$ @MartinBüttner Then, why it isn't duplicate of codegolf.stackexchange.com/questions/1255/hitting-495-kaprekar ? \$\endgroup\$
    – Xwtek
    Nov 2, 2015 at 13:14
  • \$\begingroup\$ Because it has been overlooked, I suppose. Fixed. \$\endgroup\$ Nov 2, 2015 at 13:15
  • \$\begingroup\$ @MartinBüttner Maybe add time limit make this different enough. \$\endgroup\$
    – Xwtek
    Nov 2, 2015 at 13:15
  • \$\begingroup\$ I don't know. Since you have to output the entire list anyway, there is not much you can optimise beyond actually applying the transform until you hit a cycle. If you limited the challenge to the second task, a time limit might make more sense, but then again the second task might be different enough not to be a duplicate in the first place. \$\endgroup\$ Nov 2, 2015 at 13:17
  • \$\begingroup\$ @MartinBüttner Then remove task 1 and it won't be duplicate? And add speed limit. \$\endgroup\$
    – Xwtek
    Nov 2, 2015 at 13:29
  • \$\begingroup\$ I don't even think a time limit is necessary for part 2. \$\endgroup\$ Nov 2, 2015 at 13:30
  • \$\begingroup\$ @MartinBüttner Is Task 1 still have to deleted. And please, don't discuss in the Chat, because I can't access that. Better use my email: [email protected] \$\endgroup\$
    – Xwtek
    Nov 2, 2015 at 13:57
  • \$\begingroup\$ As I said above, I don't see why you would want to squeeze both tasks into a single challenge in the first place. (How would you score answers? Sum of the two solutions?) And if you split them up, then the first answer is certainly a duplicate, but the second is fine (and if you didn't split them up, I don't see why you'd redo the same challenge as part of another challenge either). \$\endgroup\$ Nov 2, 2015 at 13:59
  • 1
    \$\begingroup\$ The cycle identification is borderline duplicate of codegolf.stackexchange.com/q/26578/194 \$\endgroup\$ Nov 2, 2015 at 14:32

Stupid leaks

Considering how immensely successful my last two challenges have been, I'll do a different style this time.

Drip, drip, drip, drip...

It's the year 3000. Due to clean air shortages, a system was created that turns water into air. However, that caused a water shortage (don't you love progress?). Therefore, a new (expensive!) system was created to convert the air back into water.

All that to say that water prices have skyrocketed.

And yet, here you are, stuck with a leaky faucet. Plumbers are expensive, but if you do it yourself, you have to order the parts online and wait for them to get here. You need a way to determine what is cheaper: calling a plumber and getting it fixed in a day, or buying the parts online but having water leak until they get here.

The input

You need to take seven positive numbers as input:

  • The price of water per gallon g.
  • The number of drops leaking per hour d.
  • The number of gallons wasted per drop z. This will always be a floating-point number less than 1.
  • The price of calling a plumber to fix it p.
  • The price of ordering the parts online o.
  • The number of hours it takes for the plumber to fix the leak l.
  • The number of hours it takes for the parts to get here s.

Only g, z, p, and o can be floats; all the rest will be counting numbers (integers greater than 0).

The task

The gallons of water wasted per hour from the leak is d*z*g. For the sake of brevity, let's call that rate R. If R*l+p is less than R*s+o, then you should print/return DIY!. If greater than, print/return Call the plumber!. If equal, print/return Whatever....


Floating-point precision through calculations is very...weird. Basically, your program can use whatever your language's default is. If you're using a language where the default floating-point type has infinite precision. If your language's default floating-point type can lose precision throughout calculations (like in Python, where .1+.1+.1+.1+.1+.1+.1+.1 != .8), then that works, too.

Short version: floating-point semantics and precision are however your language is by default.


Code-golf. Shortest wins. Standard loopholes banned.

  • \$\begingroup\$ What is a "counting number"? Does it include 0? You also might want to specify at what precision the equality will be checked (presumably hundredths?), and how rounding should be handled for the "Whatever..." case. \$\endgroup\$ Nov 2, 2015 at 18:24
  • \$\begingroup\$ @FryAmTheEggman Is this better? \$\endgroup\$ Nov 2, 2015 at 21:03
  • 2
    \$\begingroup\$ My language doesn't support floating point at all, so can I always just output Whatever...? More seriously, I'm failing to see the point of this question. Do some trivial arithmetic and then output one of three strings which between them take up 90% of the code? \$\endgroup\$ Nov 2, 2015 at 21:15
  • \$\begingroup\$ I think it is better, but I think you do have to spend a bit addressing Peter's comment about languages that don't support floats. \$\endgroup\$ Nov 2, 2015 at 23:55

Show How a Regex Is Matched

What your program or function should do:

  1. Accept input of two strings; let's call them r and s.
  2. Determine whether r is a valid regular expression (you can use any common definition of regex for this purpose, or any common definition of regexes but with lookahead and lookbehind removed; indicate which you're using). Otherwise, don't output.
  3. If so, determine whether s matches r as a regex. Otherwise, don't output.
  4. If so, output/print, in order, the part of r matched by each character of s, and also the part of s that matches it.

Note: You may use your language's regex-matching library for this.


Using PCRE; my inputs and outputs are r first and then s.

^.el*(o.*)*d\b and Hello, world!
^.ello......d\b and Hello, world

.\1\W and 800-555-1212
..\W and 00-

\b and a
\b and empty string

\d and a
no output (it doesn't match)

First floated in chat.
Not a dupe of Compile Regexes (which asks you to match regexes whereas this allows you to use the resources of your language to do so).

  • \$\begingroup\$ 1. It sure looks like a dupe to me: what's your argument for it not being a trivial transformation of the previous question? 2. In your examples, you seem to try to draw a distinction between outputting the empty string and not outputting anything. How does that work? 3. What exactly is the output format? E.g. the first example and the second example don't seem to be consistent in their treatment of metacharacters. \$\endgroup\$ Nov 5, 2015 at 22:49
  • \$\begingroup\$ @PeterTaylor 1. It's not a dupe at all: the older question asks you to match regexes whereas this allows you to use the resources of your language to do so; also, the older question outputs a means of determining matching, without regard to how it's matched, whereas this requires an output of the latter. 2. This question is OBE because of the edit I'm doing to fix #3. 3. Yeah, I messed up an example: I'll fix that immediately. \$\endgroup\$
    – msh210
    Nov 5, 2015 at 23:05
  • \$\begingroup\$ 1. With respect to the second half, see "simple transformation". But the first half is relevant, and worth editing in to the "Not a dupe" sentence. 3. I still can't figure out the output format from the examples. Obviously you want to ensure that it's not as trivial as asking the regex engine for group 0, but I think you need to first write a clear spec for the output and then write the examples (or, better, write a reference implementation to generate the examples). \$\endgroup\$ Nov 6, 2015 at 7:27
  • \$\begingroup\$ @PeterTaylor, yeah, I'll have to work on it some more. If anyone else has ideas, please chime in! \$\endgroup\$
    – msh210
    Nov 6, 2015 at 9:24

Python assembler

Python is a hybrid interpreted language. It first gets compiled into byte-code and then gets interpreted.

What does this byte-code look like you may ask? The dis module disassembles python code. Source code for dis module here

print "Hello, World!"

Gets disassembled into the following assembly.

  1           0 LOAD_CONST               0 ('Hello, World!')
              3 PRINT_ITEM
              4 PRINT_NEWLINE
              5 LOAD_CONST               1 (None)
              8 RETURN_VALUE

The output is divided in the following columns:

  1. the line number, for the first instruction of each line

  2. a labelled instruction, indicated with >>,

  3. the address of the instruction,

  4. the operation code name,

  5. operation parameters, and

  6. interpretation of the parameters in parentheses.

The disassembly of a basic for loop

for i in range(10):
    print i


  1           0 SETUP_LOOP              25 (to 28)
              3 LOAD_NAME                0 (range)
              6 LOAD_CONST               0 (10)
              9 CALL_FUNCTION            1
             12 GET_ITER
        >>   13 FOR_ITER                11 (to 27)
             16 STORE_NAME               1 (i)

  2          19 LOAD_NAME                1 (i)
             22 PRINT_ITEM
             23 PRINT_NEWLINE
             24 JUMP_ABSOLUTE           13
        >>   27 POP_BLOCK
        >>   28 LOAD_CONST               1 (None)
             31 RETURN_VALUE

Your task:

Given some python code that has been disassembled, recreate the original code object as close as you can. You can take the disassembled code through any method you chose.

Your program will output all the arguments to recreate a python code object

That is to say your program will output the following

"a string here",            
"another string here",

You can work out the variables listed above but you have to output it all, even the constants.

  • nlocals - The number of local variables
  • stacksize - The maximum number of values held on the stack at once
  • codestring - A binary containing all the opcodes and their arguments
  • consts - A tuple of constants
  • names - A tuple of global variables
  • varnames - A tuple of local names (length of nlocals)
  • lnotab - A tuple containing a map of bytecode positions to line numbers

You may use the following code to disassemble a .pyc file:

import sys, dis, marshal

with open(sys.argv[1], "rb") as code_f:
    code_f.read(8) # Magic number and modification time
    code = marshal.load(code_f)

This is code-golf, the shortest code in bytes wins

Sandbox notes

Wow that was a long one. Perhaps too long?

Is the spec completely tight?

Should I explain anything further?

Am I making it too hard for non-python entries to take part?

Should I only make it a requirement to reassemble code without any functions/classes? I'm pretty sure dis doesn't show all that.

  • 1
    \$\begingroup\$ For one thing, yes this looks very hard for non-Python entries to me. For another, I think there's too much going on at once (there's a lot to output), and you don't explain much about how to output each specific component (ideally the post should be self-contained enough to work out what to do without knowing too much about Python/dis) \$\endgroup\$
    – Sp3000
    Nov 9, 2015 at 15:41

Print a sourcecode

Given 2 inputs(First input is truthy/falsy, second input is program in same language as submission):

  1. If the first input is truthy then transform the second input into same program but printing the source code(After modification) first.
  2. If the first input is falsy then transform the second input into same program but after the program finished it prints the source code(After modification). If the program doesn't halt, you may or may not modify the program.

It's code-golf, so the shorter answer is the winner.

For example in CJam, I don't write the program to do this. (> means output)

0 q
0 0 1{_@+}11*;
>{"_~"0 0 1{_@+}11*;}_~
1 q
> {q](\o"_~"}_~
  • 7
    \$\begingroup\$ Sorry, I'm not quite sure what this question is asking. Would it be okay if you posted examples? \$\endgroup\$
    – Sp3000
    Nov 5, 2015 at 14:29
  • \$\begingroup\$ @Sp3000 Please undo your downvote. The example is fixed. \$\endgroup\$
    – Xwtek
    Nov 7, 2015 at 7:39
  • 3
    \$\begingroup\$ I didn't downvote though... \$\endgroup\$
    – Sp3000
    Nov 7, 2015 at 8:13

Vigenère Cipher

Write a program that is capable of breaking a text encyripted using Vigenère cipher encyription.


  • Take encripted text from STDIN and write plaintext to STDOUT.


  • Keyword will always be 3 letters in length.
  • Plaintext will always be in between 5-10 letters in length (inclusive).
  • All Plaintexts, Keywords and Encyripted Texts will be in English.


This is a . Shortest code in bytes wins.

I'm not sure if this is a valid and solvable question, so any suggestions are welcomed.

  • \$\begingroup\$ Dupe \$\endgroup\$
    – user45941
    Nov 10, 2015 at 18:19
  • \$\begingroup\$ I'm not sure this can actually be done without having a big dictionary for such a short piece of text. (Also, what does "encrypted texts will be English" mean?) \$\endgroup\$ Nov 15, 2015 at 15:01
  • \$\begingroup\$ @PaŭloEbermann It means they will only contain english characters, no special letters from other languages. \$\endgroup\$ Nov 15, 2015 at 15:12
  • \$\begingroup\$ Then write "consist of the letters A-Z" instead (or similar if you allow spaces and punctuation – though that needs more specification). \$\endgroup\$ Nov 15, 2015 at 15:14
  • \$\begingroup\$ For Vigenere, in general you can either try a "plaintext dictionary attack" (which means you'll have a list of valid plaintext words, like in the question linked by Mego – that would be a plain duplicate), or you try analysis of character frequencies or repetitions, which need a lot longer ciphertext in order to analyze anything useful. (Or you just output all possible plaintexts, and let the task of recognizing the correct one to some human.) \$\endgroup\$ Nov 15, 2015 at 15:19

List Style Converter



Given a list, format it into list of the choice of the input. The list will be list of item defined below, but it can be multidimensional.

List Styles

There is 2 list separators:

  1. Space
  2. Comma

    For one dimensional list, only one separator is accepted. Space and only space between item is considered as separator. It is impossible to have more than 2 dimension without enclosing list of second dimension or third dimension. when parsing list, comma takes lower precedence and it is parsed with least dimension as possible. Space is optional between ] with [; } with {; and ) with (

    There is 3 list enclosure:

  3. [...]

  4. (...)
  5. {...}

    Closing bracket must be present.


There is 2 types of item, another list or those following regex [0-9a-zA-Z]* or everything enclosed with single quote or double quote. If enclosed with single quote, it can contains double quote and vice versa. There is no zero-length item

Here is valid non-list item

"Hello, world!"
"It's house."

Here is the list

Hello, World!
Space then it is list

Here is invalid item.



The input consist of string of number then space then list as defined above. The number indicates the output format.

There are n digit of number where n is dimension of the input array. each number correspond with this one. (Table formatting needed). The dimension is counted from outer into inner. You may assume that there is no two 0 or 1 without being separated by 2 - 7.

  1. 0 = unenclosed comma list
  2. 1 = unenclosed space list
  3. 2 = parantheses enclosed comma list
  4. 3 = parantheses enclosed space list
  5. 4 = square bracket enclosed comma list
  6. 5 = square bracket enclosed space list
  7. 6 = curly bracket enclosed space list
  8. 7 = curly bracket enclosed space list


A identical list but with formatting changed according to input (i.e. each item it list is identical). Space not between list is allowed

Test cases

> denotes output # denotes comment

6 Hello, world
> {Hello world}
5 (1, 1, 2, 3, 5, 8, 13, 21)
> [1, 1, 2, 3, 5, 8, 13, 21]
> [1,1,2,3,5,8,13,21]
> [ 1,1, 2,3, 5,8, 13,21 ]
#But it is invalid
> [1,1, 2,3, 5,8, 1 3,2 1]
> [1,1,2,3,5,8,13,21,]
10 Hello, I am doctor
#Parsing rules that space separator bound tighter
> Hello I,am,doctor
01 Hello, I am doctor
> Hello, I am doctor
0 "Not to be confused be space or comma in a quoted item"
> "Not to be confused be space or comma in a quoted item"
51 [1,2] [3,4]
> [1 2,3 4]
51 [1,2][3,4]
> [1 2,3 4]

Sandbox Question.

The format needs helps. Needs pointing when there is ambiguity.

  • \$\begingroup\$ I'm not sure that I fully understand this. To take a couple of your examples, Hello, World! appears to have two separators (a comma and a space): is it a one-dimensional three-element list, or a two-dimensional list? Is () a one-dimensional list or a two-dimensional list? And in the input, which order are the dimensions listed in, and what constraints are there on which formats can be used at which levels? (E.g. 00 is clearly not going to work, but I'm not sure whether 010 is permitted). \$\endgroup\$ Nov 16, 2015 at 23:20
  • \$\begingroup\$ @PeterTaylor That's why I post the challenge here, because this challenge is nontrivial to writing. It is one dimensional comma separated list. Only space between item is list separator. Comma (except inside quote) isn't valid part of item. The input order is from outer into inner. You can assume that 00 and 010 isn't never entered. \$\endgroup\$
    – Xwtek
    Nov 17, 2015 at 8:35
  • \$\begingroup\$ () is one-dimensional list since you have to it is parsed with least dimension as possible \$\endgroup\$
    – Xwtek
    Nov 17, 2015 at 8:43
  • 1
    \$\begingroup\$ I'm afraid that I'm even more confused than before about spaces and commas. You seem to be saying that in the example 6 Hello, world a (comma plus space) makes a single separator in a one-dimensional list, whereas in 10 Hello, I am doctor a (comma plus space) is two distinct separators in a two-dimensional list. Do you have a reference implementation which we might be able to use to reverse-engineer the spec while the question is still in the sandbox? \$\endgroup\$ Nov 17, 2015 at 16:55
  • \$\begingroup\$ In "Hello, world", "Hello" and "World" can be 1-item space separated list, however, lowest dimension takes precedence. In "Hello, I am a doctor" It is list containing 2 item. One is 1-item list, other is 4-item list. \$\endgroup\$
    – Xwtek
    Nov 18, 2015 at 9:56


The diagram of the triangle the program needs to solve.

This is a challenge where you have to work out the length of a given w and h.

To qualify as a correct solution:

  1. The program uses STDIN to get the values of w and h.
  2. The program uses STDOUT to output the value of a in the above diagram.

The shortest code in bytes wins.

Tags: code-golf, maths

  • \$\begingroup\$ What's the formula? Unless it's very complicated, I expect it will be totally straightforward to golf. \$\endgroup\$
    – xnor
    Nov 18, 2015 at 11:45
  • 1
    \$\begingroup\$ @xnor, a = w/2 * sin(atan(h/w)). The diagram throws in some irrelevancies and omits a relevant line, but it's not an interesting problem. \$\endgroup\$ Nov 18, 2015 at 13:02
  • \$\begingroup\$ @Peter Should I post this or do you think it's too easy? \$\endgroup\$
    – Oliver
    Nov 18, 2015 at 21:31
  • 1
    \$\begingroup\$ @Tobsta I think it's too straightforward. Languages with trig will use the formula Peter gave, and the rest will do something like h*w/sqrt(h*h+w*w)/2. \$\endgroup\$
    – xnor
    Nov 18, 2015 at 21:58
  • \$\begingroup\$ @xnor Ok, got it \$\endgroup\$
    – Oliver
    Nov 18, 2015 at 22:54

Wildcard Golf


I've read this problem long time ago somewhere but I still don't know what's the best solution, so I'm posting it here. I don't remember the original author or wording so here is all in my own words.

This is different from regex golf because only two wildcards, * (equivalent to the regex .*) and ? (equivalent to the regex .), are allowed.


You are given two lists of strings. You need to generate the shortest wildcard that matches all strings in the first list (the wanted-list) and none in the second list (the unwanted-list). In the wildcard, you can use * to match 0 or more chars and use ? to match any one char.

For simplicity we can assume that inputs only have lowercase English characters and each string won't be longer than 100 characters. But the list can be very long (like several thousand), so speed of your program is important.

The correct answer that has the lowest average-case theoretic time complexity wins. In a tie, an easier-to-read answer wins.

Example Input and Output


  • Wanted list: abacum, academ, alarm, adam
  • Unwanted list: alien, african, atom

One possible output: a?a*

I'd also like to hear about how to approach this problem, and how to prove the theoretic lower bound of time/space complexity.

I'm new to this so comments are welcome. I'm not sure if my winning criteria is clear and practical. Also I don't know what tags I should put there. This is not a code-golf question.

  • 1
    \$\begingroup\$ It's already been done \$\endgroup\$ Nov 17, 2015 at 21:46
  • \$\begingroup\$ Thanks for pointing it out @peter-taylor. This challenge is different in terms of using wildcards, not regex. So you think it is not worthy to post? \$\endgroup\$
    – Yan Li
    Nov 17, 2015 at 22:06
  • \$\begingroup\$ Ah, I thought you were using wildcard as a synonym of regex. I take the point that removing alternation does make quite a different problem. Although it has the downside that there are insoluble cases (e.g. I don't think your wildcards can separate a wanted list of a and abba from an unwanted list of aba), so you'd need to specify how those cases should be handled. \$\endgroup\$ Nov 17, 2015 at 22:16
  • \$\begingroup\$ Thanks! I'll edit and clarify these concerns. \$\endgroup\$
    – Yan Li
    Nov 17, 2015 at 22:18

C++ Expression Matching

So, I like C++. And I like regex matching puzzles (heck, "regex golf" is what first got me lurking on this site). Might as well try to sort of combine the two!


Write a full program that takes as input two lists of zero to five integers in the range [1, 127], and outputs a string representation of a C expression that evaluates to nonzero / true for all integers in the first list, and zero / false for all integers in the second list. Input can be taken in any convenient form.

As a special case, if the second list is empty, then the expression returned must evaluate to true for only the integers in the first list, and false for all other integers in the range [1, 127]. Likewise, if the first list is empty, it should evaluate to false for the integers in the second list, and true for all others in that range.

The program will not receive two empty lists as input. If both lists are non-empty, there are no requirements on the result of the output when evaluated with an integer not in the input. (any return value is fine, as is undefined behavior, division by 0, etc).

The following tokens may be used in the expression:

  • Integer literals in decimal, hex, or octal, with optional U and/or LL suffix to denote unsigned / long long ints.
  • A single int variable, which will contain each of the integers from the input in turn. The variable can have any legal variable name.
  • Any of the unary operators + - ! ~
  • Any of the binary operators + - * / % << >> < > <= >= == != & | ^ && || ,
  • The ternary operator ?:
  • Parentheses.
  • Operators that mutate their arguments (++ --, = += -= etc.) are not allowed.
  • Character literals ('a', '_', '\0', etc.) are not allowed.

Some examples of possible outputs:

true            false           sample expression
[1, 3, 5, 7],   [2, 4, 6, 8]    c%2
[5, 6, 10],     [2, 8, 16]      t&~-t
[7, 14, 21],    []              22>x&!(x%7)

(TODO: Specify undefined / implementation-defined behavior details? My test program assumes 32-bit ints / longs, 64-bit long longs, and "nice" two's-complement signed overflow / conversion.)

This challenge is ; your score is determined by the total number of characters in the outputs for these ten randomly-generated inputs: (TODO).

Bonus: Subtract 15 from your score if the output expression evaluates to 1, not just nonzero, for all 'true' inputs.

Sandbox Questions

Welp, turns out my "Round Fractions" question from earlier is pretty much a subset of "Closest fraction". So here's another idea I've been tossing around since the one challenge I answered in C a while back (Area of an ASCII Polygon).

This is still very much a work-in-progress spec, though; some questions I have:

  • I believe this could be tagged as C rather than C++; the only difference I'm aware of is the ternary conditional's precedence, and given that no assignment operators are allowed, it might not make a difference.
  • I'm not sure what tags would go best on this (is it if the output isn't fixed?)
  • I imagine there should probably be some additional constraint to prevent theoretically optimal but impossibly slow brute-force searches.
  • The range [1, 127] is kind of arbitrary; my thought is that it should be able to handle anything in ASCII range + whitespace characters, but not much more than that, so as to make the special cases less restrictive.
  • Would there be a way to spin this off as , if establishing run-time conditions is too arbitrary?

I'm mostly done writing a program to test the output expressions; just need to do a bit more testing.

That's pretty much it; hopefully this is enough to work with for feedback. Thoughts / comments?

  • \$\begingroup\$ Interesting challenge. I think a time-limited code-challenge is a better fit than code-golf, because there's a lot of complexity with that many operators and golfed code would be hideous. I think the random test cases should be supplemented with some which are designed to favour different operators, so that deciding to leave some out for speed becomes a real trade-off. There's only one integer literal which anyone would want to use in octal, so you could make a special case for 0. If you're going to allow LL in tokens then you really should be explicit about type widths. \$\endgroup\$ Nov 26, 2015 at 21:01

Typographic Chemistry

Inspired by this: https://xkcd.com/1442/


You must make a program or function that take input a string from STDIN and output the possible allowed reactions (1 point per unique reaction, see also "Score" below)


A chemical reaction is allowed if all the "legs" of the elements are used, i.e., there are no unpaired "legs". A "leg" is just the end of a curve in the typographic print of the chemical symbol (see the comic and it should be clear). So for example:

Carbon - C - 2 legs

Oxygen - O - 0 legs

Hydrogen - H - 4 legs

Nitrogen - N - 2 legs

Potassium - K - 4 legs

Phosphorus _ P 1 leg

An element can be rotated, reflected but not stretched in any way, so that the only possible bonds are (here I don't know how to rotate the chars, if somebody can help it would be welcome):

$$CH \;\mathrm{(with\;the\;C\;on\;top\;or\;bottom\;rotated\;by\;90\;degrees)}\\CK \;\mathrm{(with\;the\;C\;on\;top\;or\;bottom\;rotated\;by\;90\;degrees\;or\;to\;the\;right\;rotated\;by\;180)}\\ HK\;\mathrm{(on\;top\;of\;each\;other\;or\;on\;the\;side\;rotating\;one\;by\;180)}\\ NN\;\mathrm{(with\;one\;reflected\;has\;two\;legs\;on\;top\;and\;two\;diconnected\;legs\;on\;bottom)}\\ P\;\mathrm{(with\;anything)}\\ O\;\mathrm{doesn't\;bond}$$

These are the only possible elements passed from STDIN. Notice that the difference between H and K is that K can bond also laterally with a C.

Extra Rule

If no reaction is possible, the output should be equal to the input


1 point per reaction. Bonus: X3 the score if you can print the reaction diagramatically, i.e. print the shape of the molecule (like in the comic)


$$Input \rightarrow Output\\ C\,C \rightarrow (C_2)\\ N \, N \rightarrow N \, N\\ C\,N \, N\,P\,P \rightarrow (C N_2 P_2)\\ C\,C\,K \, H\,H\rightarrow (KC_2H_2)\\ C\,H\,O\rightarrow C\,H\,O $$

  • \$\begingroup\$ Your rules seem to be imposing extra grid-alignment constraints on the letters (e.g. you don't seem to permit the hydrogen crystal from the xkcd). Does that mean that although P can bond with anything except O, the positions in which it can do so are restricted? \$\endgroup\$ Nov 24, 2015 at 19:05
  • \$\begingroup\$ Hi, I don't want to impose necessarily the extra grid alignment, thanks for noticing it. Yes, P can bond with anything, I added it so that it is easier to have "allowed" reactions. \$\endgroup\$
    – Costantino
    Nov 25, 2015 at 15:01
  • \$\begingroup\$ So does that mean e.g. that CP_2 is possible? \$\endgroup\$ Nov 25, 2015 at 15:12
  • \$\begingroup\$ yes it is, although I have no idea how you could print it. Do you have any good way to state the rules simply and effectively? \$\endgroup\$
    – Costantino
    Nov 25, 2015 at 15:39
  • \$\begingroup\$ This is so far from the truth of chemistry that you really need some decent drawings to show what's acceptable. The number of bonds an atom can make is in reality determined by its column in the periodic table: K=1 (except the bond is usually ionic not covalent), H=1, C=4, N=3, P=3 (sometimes 5), O=2. \$\endgroup\$ Nov 25, 2015 at 23:25
  • \$\begingroup\$ Hi, I have prepared an image, but I can't upload it because I don't have enough reputation. Can you help me? \$\endgroup\$
    – Costantino
    Nov 26, 2015 at 16:06
  • \$\begingroup\$ The easiest solution I can see is to remove entirely the list of possible bonds and the bonus and to effectively convert it into a question of whether there exists a graph with the desired degree sequence. IMO that's still an interesting question, and one which hasn't been asked here before. \$\endgroup\$ Nov 26, 2015 at 21:08

Note: I think the question is fine. I just need some more testcases for it.

You are given the priority order of alleles for a particular trait. For example,


means that A and B are equally dominant and O is recessive to both of them. An organism has exactly two alleles, but only the dominant trait(s) is/are expressed. So an organism with gene AO will express only A but an organism with gene AB will express both A and B. An organism with two same alleles will express that allele only.

Each offspring will receive two alleles - one from the mother and the other from the father. So if the initial parents are AB and AO, the offspring formed will be:

AA - 25%
AO - 25%
AB - 25%
BO - 25%

Expressed traits will be

A - 50%
AB - 25%
B - 25%

Offspring of one generation may breed only with a single member of the opposite sex in the same generation during its lifetime. Assume for the sake of this challenge that every male finds a random female in the same generation and has exactly two children - one male and one female. Siblings may interbreed. Note that, except for the first generation, we can ignore the sex of the individuals as their sex chromosomes assort independently of their other characteristics.


  • Priority order of all alleles (may include unnecesary alleles)
  • Genotype of every organism in initial generation
  • Number of generations created
  • Any one allele
  • (Optional) Number of lines of input for priority order (for languages like C++)


  • Probability of the specified allele existing in a randomly selected individual in the specified generation (accurate to three decimal places)


  • Once two/three answers are posted, I'll use the same testcases in all of them to see which of them are faulty.
  • After a week (or I could prolong the deadline) I will upload a lengthy test case in a few days. The code that solves it in the fastest time wins.

Sample data (Some simple testcases)


Male(s) - AA
Female(s) - AB

Output 0


Male(s) - AA
Female(s) - AB

Output 0.75


Male(s) - AC,BD
Female(s) - AC,BC

Output 0.125

  • 1
    \$\begingroup\$ "Once two/three answers are posted, I'll use the same testcases in all of them to see which of them are faulty" You should have a way to verify answers without using other answers. \$\endgroup\$ Dec 1, 2015 at 17:35
  • \$\begingroup\$ @FryAmTheEggman I am abandoning this Q, anyone else is free to post it themselves. \$\endgroup\$ Dec 2, 2015 at 9:47

Cops and Robbers - Find the Formula

Cops will write a function that takes numerical inputs and produces numerical outputs (note - outputs can be any base and may contain letters). They will post the language, the number of bytes it takes to write the code (up to 128), rounded up to the nearest power of 2, as well as a minimum of 2 test cases. The robbers will try to write a program that takes the same numerical inputs as the test cases and produces identical outputs.

Note - PRNG's, hashing, and other forms of encryption are not allowed.


Cops (if safe)

The floor of the product of:

  • 128 divided by the power of two rounded up for the bytes
  • The natural logarithm of the number of test cases

If cracked, -10 points.


The floor of the quotient of

  • Half the number rounded up to by the cops
  • The natural logarithm of the number of test cases
  • \$\begingroup\$ Say I have a function f(x) that returns x when x<2 and 3*x ᴏtherwise. Would the robber's function only have to match the given test cases, or have to match all test cases? \$\endgroup\$ Nov 27, 2015 at 3:06
  • \$\begingroup\$ @CᴏɴᴏʀO'Bʀɪᴇɴ The given test cases only. \$\endgroup\$
    – Arcturus
    Nov 27, 2015 at 3:16
  • \$\begingroup\$ Is there a maximum of test cases? \$\endgroup\$ Nov 27, 2015 at 3:24
  • \$\begingroup\$ @CᴏɴᴏʀO'Bʀɪᴇɴ I'm not sure if there should be. If there were, I'd say maybe 10 or 12. \$\endgroup\$
    – Arcturus
    Nov 27, 2015 at 3:25
  • \$\begingroup\$ I think the scoring algorithm might be a bit complex. \$\endgroup\$ Nov 27, 2015 at 3:41
  • \$\begingroup\$ @CᴏɴᴏʀO'Bʀɪᴇɴ I want to do something that awards points depending on the number of test cases because that makes it more likely that the robber found the intended solution and is "more" right. \$\endgroup\$
    – Arcturus
    Nov 27, 2015 at 5:03
  • 2
    \$\begingroup\$ The cops-and-robbers lesson which everyone should have learnt by now is that built-in crypto functions should be banned because otherwise the cops have an easy time. \$\endgroup\$ Nov 27, 2015 at 13:49
  • 1
    \$\begingroup\$ ^ That should include hashing and PRNGs. Although it's really hard to rule them out conclusively. My personal goal is still to come up with more CnRs that aren't susceptible to stuff like that in the first place (like my Programming Language Quiz). \$\endgroup\$ Nov 27, 2015 at 14:00
  • \$\begingroup\$ @MartinBüttner Given that I've explicitly disallowed hashing, PRNGs, and encryption, what do you think of this challenge? \$\endgroup\$
    – Arcturus
    Nov 27, 2015 at 22:15
  • \$\begingroup\$ @Eridan It's still susceptible to arbitrary base conversions or expmod (just check out any CnR-submission by Dennis to see some examples). People can just throw together a quasi-random program in a golfing-language without having to understand it and just run some numbers through it to generate test cases. \$\endgroup\$ Nov 27, 2015 at 22:36
  • \$\begingroup\$ @MartinBüttner I didn't realize those were bad for CnR challenges (I even mentioned base conversion above). Is there a specific way I could describe methods like those to disallow them? \$\endgroup\$
    – Arcturus
    Nov 27, 2015 at 22:50
  • \$\begingroup\$ @Eridan none I can think of. That's why I meant that this is an inherent problem of any CnR that lets participant choose what their program does. In CnRs where the programs need to solve a specific task, this is not such a big issue, because the cops actually need to find a convoluted but working implementation themselves. \$\endgroup\$ Nov 27, 2015 at 23:07
  • \$\begingroup\$ Even with crypto banned, numerical functions make for boring CnR challenges since it's much more likely to be about finding parameters rather than guessing the structure of the code. \$\endgroup\$
    – xnor
    Nov 28, 2015 at 9:57
  • 1
    \$\begingroup\$ A problem: Anyone can just write an interpolating polynomial. \$\endgroup\$ Nov 28, 2015 at 13:49


Quiddler is a card game where you try to create words from letter cards drawn from a deck. A word is defined as being more than 2 cards in length. Sometimes letters are combined on cards in this game, however that will not be the case in this challenge.

Your mission is to write a program which creates words from the letters read in on standard input. Your dictionary of words is the words file on any standard unix system. You may assume that all strings this file is all lowercase.


The string of letters you can use to create words is read in on standard input. This string will be all lowercase, and will not have any spaces in it.

Valid examples are:


Invalid are:

klj kljklj djkas;


The list of all possible results from said string each string. Remember you can produce multiple words in the same answer.

Examples of valid output include. Please remember that I came up with these off the top of my head, and may not be complete. Input is left aligned and the output is presented as the indented lines. The -> is for your benefit.

tacb  -> 

fivquedrr ->
         five qud
         quid five

The order of the solutions output does not need to be in any specific order.

The environment

This program must run in a standard UNIX-like environment. This means that you may use any standard shell (bash, ksh, csh, zsh, fish), and you have access to all the standard tools. This challenge is restricted to the shell scripting languages.

The path to the dictionary file in the environment variable, DICT, the path to the file should not be in any valid solution. Use $DICT as the path to the dictionary. This is included so that you can provide testing instructions for your program.


The winner is the one with the fewest bytes of code that produces the correct output.

  • \$\begingroup\$ In the example output, I'm not sure why for the first input the output is newline-separated, but for the second it's space-separated. I also don't understand the second paragraph in the section "The environment". \$\endgroup\$ Nov 27, 2015 at 21:30
  • \$\begingroup\$ @PeterTaylor In quiddler you can have multiple words per possible solution. I'll add a second example to demo. \$\endgroup\$
    – HSchmale
    Nov 27, 2015 at 21:53
  • \$\begingroup\$ So is this basically a variant on Countdown where the dictionary is amplified by including its Cartesian power? \$\endgroup\$ Nov 28, 2015 at 8:08
  • \$\begingroup\$ @PeterTaylor: Pretty much, except I did not know that existed. Also, for each answer you can only use each answer once. \$\endgroup\$
    – HSchmale
    Nov 28, 2015 at 16:43

Ancient Language Translator

<insert a silly story here>


Write a program that takes an English sentence and translates it into the Ancient Language. You have to implement at least 42 words. For the purpose of this challenge, you do not have to care about special rules such as "(may be shortened to al when used as a prefix, as in albitr)".


An English sentence.


A translated version of the input, simply replace the English words with the Ancient ones.


To be added.



  • 2
    \$\begingroup\$ This might be considered as too broad as there is no specific words to implement. For scoring a code-challenge might work with the score being something like the sum of the length of all words implemented. code-golf might also work. Kind of related challenge. The title is also possibly misleading, so I'd suggest putting "Ancient Language" in quotes \$\endgroup\$
    – Downgoat
    Nov 29, 2015 at 16:55
  • \$\begingroup\$ I think this would be uninteresting just because it's just replacement, not actual translation. \$\endgroup\$
    – cat
    Nov 30, 2015 at 3:07
  • \$\begingroup\$ @sysreq Translating English into the "Ancient Language" is just replacement as far as I know... \$\endgroup\$
    – Stefnotch
    Nov 30, 2015 at 17:24
  • \$\begingroup\$ @Downgoat Oh, ok! So, what words should have to be included? A selection of) the most common words: en.wikipedia.org/wiki/Most_common_words_in_English \$\endgroup\$
    – Stefnotch
    Nov 30, 2015 at 17:26

Nested Header List

The goal of this challenge is to complete a list of consecutive nested header numbers when given a start and an end. When given 1.1.1 and 1.1.5 you should generate 1.1.1, 1.1.2, 1.1.3, 1.1.4, 1.1.5

Specific Rules

  1. Your entry must take in a start, end, and multiple optional range parameters. Parameters can be taken form STDIN (or nearest equivalent) or a file.
  2. Your entry may assume valid input
  3. Input will be of the following format:
    1. start and end will be strings of . delimited integers of the same length
    2. start and end will have three segments; (1) set values, (2) iterator, (3) trailing values.
      • The iterator is the first value which differs between start and end.
      • The set values are the values before the iterator. These values never change
      • The trailing values are the values after the iterator. These values iterate up as determined by the range parameter(s). All trailing values will be 1.
    3. range will be a list of integers with a length corresponding to the number of trailing values. When there are no trailing values, range is not specified. The value of range corresponding to each trailing value determines the inclusive upper bound which that entry iterates to.
  4. Output will be to STDOUT (or closest alternative) and will show each value separated by at least one delimiter. Delimiter can by any character or string of characters, but it must be consistent. Output must be sorted correctly


start = '', end = '', range = [5]
                                                  previous value is iterated
                                                  only when iterating value
                                                  limit set by range

start = '', end = '', range = [5]

start = '', end = '', range = [5,2]

This is code golf so shortest code by bytes wins.


  1. Allow trailing values to be values other than 1 in end parameter - 12.5% off
  2. Handle incorrect number of values in range parameter - 12.5% off
  3. Handle end less than start by producing list in reverse - 50% off

Count the Connect Four Positions

Connect Four is a two-player game on a rectangular board. The board is m spaces wide and n spaces tall, and players alternate placing pieces in columns. A placed piece always fills the lowest empty space in a column, and a player may not move in a full column. In the standard game, m=7 and n=6.

The game ends when one player completes a row of four pieces vertically, horizontally, or diagonally, or all m columns are full. The edges of the board do not wrap.


Write a program or function to determine the number of distinct, legal m by n Connect Four boards after p plies. (A ply is one move by one player.) A legal position is one reachable from the empty board through a sequence of moves in which no player had already won. (A position in which one player has just won is legal.)


You may assume that 0<=p<=m*n, m<=8 and n<=8.

As usual, hardcoding is not allowed.

Your code should be at most 1024 bytes in length, and use at most 16 GB of memory.

Related: Determine winner of Connect 4

Test cases

[need to add; include OEIS]

Relevant links:


Compile from Brainfuck

The professors at Brainfuck University realized their jobs are horrible, because all they do is discuss quantum mechanics using Brainfuck, so they decided to take their programs and compile them to a better language. Because of the randomness of quantum particles, their program needs to be small so it has a smaller chance of being disrupted in the Higgs Field.

Your task is to get a Brainfuck program from any input and output that program transcompiled into another language. Here is an example:


Compiles to the C program:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv) {
    unsigned char *cell = calloc(30000, 1);
    unsigned char *cells = cell;
    if (!cell) {
        fprintf(stderr, "Error allocating memory.\n");
        return 1;
        //actual program

        return 0;


Your score is the size of your program added to the size of the output.


  • 3
    \$\begingroup\$ Dupe \$\endgroup\$
    – user45941
    Dec 5, 2015 at 9:55

Logic Puzzle Solver/Inference Engine

Your goal is to take the clues and other facts given in a grade-school logic grid puzzle such as these and solve the puzzle. To keep things simple, your program will only solve specific logic problems about which it can make the assumptions you wish to hard-code in, but the program need not perform any checks to see if those assumptions can be made.

You may not use:

  • A declarative language
  • Any function provided - by an external dependency - for the solving of a logic puzzle.


Your program will take input from the command line. After gathering assumptions, the program will ask for facts written as such:

subject.verb object

for all true facts. For false facts:

!subject.verb object

Examples: If Chad bought donuts,

Chad.bought donuts

If he didn't:

!Chad.bought donuts.

If Nancy's last name isn't Wesley,

!Nancy.is Wesley.


Your program will output its conclusions as such:

subject verb object.

So, if your program determines that Chad bought donuts and Nancy's last name is Wesley, then it will output:

Chad bought donuts.

Nancy's last name is Wesley.
  • 3
    \$\begingroup\$ The "these" link goes to a login page. I'm not going to create an account on some random site just to find out what the spec is. \$\endgroup\$ Dec 15, 2015 at 22:24
  • \$\begingroup\$ "You may not use a declarative language" :-( \$\endgroup\$
    – Fatalize
    Dec 16, 2015 at 12:59
  • \$\begingroup\$ Does "is" always refer to someone's last name? If not, how can our code know the difference between Nancy.is Wesley and Nancy.is chef? \$\endgroup\$
    – Luke
    Dec 16, 2015 at 14:49

New user to Programming Puzzles!


I would like a king of the hill challenge for bots playing the game of spades. Spades is a card game. The rules are shown on wikipedia.

Scoring rules:

  • Nils allowed, with 50 points for completion (not 100). -50 for losing.
  • 10 points a hand, with sandbagging allowed.
  • Partnership Playing
  • Sum of all four players hands cannot equal 13!

Winner is first to 500 points. The bot will be paired with all other bots entered into the competition. The pair of winners will be crowned with +10 meta-points (Mpoints), losers will get -1 Mpoints. Whoever has the most Mpoints wins - ties based upon sum of points earned in the games.


  • The bot with the lowest Mpoints bids first. Bidding proceeds from down until reaching 4th slot, then goes back to first slot and continues. Play starts with this player.
  • The bot will be given a string of cards - AS for Ace of Spades, JC for Jack of Clubs, 2D for 2 of Diamonds, 8H for 8 of hearts, randomly dealt from a single 52-card deck. Each will be comma separated: AS,JC,2D,8H,4C,5S,8D,3D,3S,JS,10S
  • The bot will get the bids from the other bots before making the bid.
  • Upon winning a hand, the bot gets to continue making plays until someone else wins the hand.
  • Hands are scored at the end using the scoring rules. If a team's score is less than 500, gameplay continues with a new hand.

Unfortunately, I do not know how to setup the servers or any of that stuff. I just think the challenge will be interesting. If anyone can help with that, run with it. I like to watch these challenges unfold - but I'm too much of an engineer and not enough of a programmer to make these kinds of programming happen.

  • \$\begingroup\$ You should fully list out the rules in the body of the question - it's considered poor form for challenges to require exterior resources to be fully understood. \$\endgroup\$
    – user45941
    Dec 22, 2015 at 22:56

I was thinking about a challenge on wrapping time.

I am a member here for 34 days now. I would have expected for the date to wrap to 1 month.


  • starting with hours from the joining date to now.

  • first wrapping happens when you go over 24 hours, the count will be in days now.

  • second wrapping happens after reaching 30 or 31 days, you can decide, to months.

  • third wrapping really wraps when a year is reached, it shall be displayed as i.e. 2 years 3 month.

  • round to neares full unit, i.e. 43 days = 1 month, 50 days = 2 month

  • take either a build in function to get the current time or hardcode it to ´2015-12-19-11´ <- time when challenge will be posted. If hardcoding it is shorter you may take the bytecount from the hardcoded version.

  • Dates after the current or hardcoded date can do whatever.


The joining date and hour like ´YYYY-MM-DD-HH´ the delimeter does not have to be a - choose whatever you like.


The time according to the rules above.


In: 2015-12-10
Out: 9 Days

In: 2015-10-28
Out: 2 Month
  • \$\begingroup\$ I believe I saw a challenge about wrapping 24-hour time that may be related, but not a duplicate. Also, what date are we calculating the difference from? \$\endgroup\$ Dec 18, 2015 at 17:05
  • \$\begingroup\$ that would be the date right now or a set date if no build in is available \$\endgroup\$
    – Eumel
    Dec 19, 2015 at 8:19
  • \$\begingroup\$ I think it should be either a built-in date or another date given from input for all languages, to make things fair. \$\endgroup\$ Dec 19, 2015 at 16:02
  • \$\begingroup\$ I wanted it to be non input, how would you suggest doing that? \$\endgroup\$
    – Eumel
    Dec 19, 2015 at 20:01
  • \$\begingroup\$ Use a built-in date such as 01-01-2015 (or 01-01-2000, depending on what the date range should be). The program should not be required to accept dates before that. \$\endgroup\$ Dec 20, 2015 at 21:14

Browser identifier

There are three major browsers at the moment, Internet Explorer, Google Chrome and Firefox. Sometimes, the JavaScript engines inside of these browsers work a bit differently, and that can break some applications. Therefore, we need a way to identify what browser the user is currently using!

Your answer should be a JavaScript program or function, that when run on the latest version of a browser, should output a string representing that browser. The string outputed could be anything, as long as it stays the same every time you run it. Output should go to a HTML paragraph with id O, console.log, or as return value.

Please put your answer in a snippet, along with <p id="o"></p> in the HTML section if your answer uses it.

(scoreboard snippet goes here)

  • 1
    \$\begingroup\$ I believe Javascript has a builtin for this. It may be best to forbid using it. \$\endgroup\$ Dec 22, 2015 at 17:34
  • \$\begingroup\$ @SuperJedi224 Well, I did some searching before, and I found this thread on SO, and the highest voted answer was a big mess, and no answer was very short and reliable. There is this other thread, and it has some that could be golfed a bit, but there isn't really one function / builtin that checks the browser. \$\endgroup\$
    – xenia
    Dec 23, 2015 at 2:56
  • \$\begingroup\$ You might need to freeze the version numbers of the 3 browsers, or else require that answers specify version numbers. \$\endgroup\$ Dec 29, 2015 at 15:54

Parse a tree for pruning

Windows supplies users with tree: a neat little tool that converts a directory tree to ASCII-CP437 art. It's a very human-readable format. However, it's a bit useless if you want the directory tree of an entire drive, or even just the Windows folder, as it's very hard to prune the parts you don't want. Hence this challenge.


Your task is to produce a function or program that will convert the tree from one or both of the input formats into one or more of the output formats. The smaller your code, the more of a head start you have.


There are two types of input that you might be given:


This is the default.

Folder PATH listing for volume Main Drive
Volume serial number is 00F3-F586
│   explorer.exe
│   notepad.exe
│   virus.dll
│   write.exe
│   │   BootDebuggerFiles.ini
│   │   
│   ├───DVD
│   │       your.txt
│   │       
│   ├───EFI
│   │       pc.txt
│   │       
│   ├───Fonts
│   │       has.txt
│   │       
│   ├───PCAT
│   │       been.txt
│   │       
│   └───Resources
│           wrecked.txt


This will be easier to parse for many languages.

Folder PATH listing for volume Main Drive
Volume serial number is 00F3-F586
|   explorer.exe
|   notepad.exe
|   virus.dll
|   write.exe
|   |   BootDebuggerFiles.ini
|   |   
|   +---DVD
|   |       your.txt
|   |       
|   +---EFI
|   |       pc.txt
|   |       
|   +---Fonts
|   |       has.txt
|   |       
|   +---PCAT
|   |       been.txt
|   |       
|   \---Resources
|           wrecked.txt


There are several possible types of output you can return, each suited to a different type of language.

Array / List hierarchy of strings

The first element of each array / list is the name, the rest are the contents. Files should be represented by strings, empty folders should be represented by a single-length array containing one string. Note: This should be returned from a function as an array / list, not printed as a string.

["C:\WINDOWS", "explorer.exe", "notepad.exe", "virus.dll", "WLXPGSS.SCR", "write.exe", ["Boot", "BootDebuggerFiles.ini", ["DVD", "your.txt"], ["EFI", "pc.txt"], ["Fonts", "has.txt"], ["PCAT", "been.txt"], ["Resources", "wrecked.txt"]], ["System"], ["System32", "cmd.exe", "conhost.exe", "winlogon.cmd", "winlogon.exe"]]

Object / Dictionary

Similar to array / list, but a little more intuitive. Folders should have the value of their contents as another object / dictionary. Files should have the value "FILE".

{"C:\WINDOWS":{"explorer.exe":"FILE","notepad.exe":"FILE","virus.dll":"FILE","WLXPGSS.SCR":"FILE","write.exe":"FILE","Boot":{"BootDebuggerFiles.ini":"FILE","DVD":{"your.txt":"FILE"},"EFI":{"pc.txt":"FILE"},"Fonts":{"has.txt":"FILE"} [...] } [...] } [...] }

Lisp-style string

Similar to array / list, where the head of the list is the directory name and the tail is the contents. An empty directory is a list with no tail, and a file is a string.

No WAY am I putting an example. No way. I've spent half the time on this question creating the examples. No way. Ok, maybe later.


If you satisfy none of these bonuses, your submission is still valid. But its score shall infinite, so it is non-competitive.
These bonuses are to multiply your score by. Bonuses stack by multiplication. These bonuses must all be achieved consistently to be awarded.

  • 100% Allow at least one input mode and output mode
  • 50% Allow both input modes
  • 90% Output in exactly two ways
  • 50% Output in one of two ways depending on parameters
  • 80% Output in exactly three ways
  • 25% Output in one of three ways depending on parameters

Identifying spies in "Resistance"

This is still very rough, but I think it has the makings of an interesting challenge. Please help me improve it. What do I need to add? What do I need clarify?

Resistance is a party game that pits "resistance members" against "imperial spies" on a series of missions. A very important aspect of the game is that the resistance members do not know who the spies are, whereas the spies do know who is who.

How the game works

The relevant details of the game will be added here. For now, just check the Wikipedia page linked in the title.


your challenge is to write a program that takes as input the details of every round and outputs who it thinks is a spy after each round. There are 5 rounds (missions) in a game of resistance, so the program/function will take in all the data for the first round, which includes

  1. Each proposed team to go on the mission
  2. Each public vote following each proposal
  3. The final team to go on the mission
  4. The outcome of the mission (i.e. how many passes and how many fails)

It will then output who it thinks is a spy. It will then do the same for each subsequent round.

Important Details

We will be playing resistance for (6?) people, A, B, C, D, E, and F.

Input format is flexible. It may be done round by round or all at once. However, since ach submission is outputting something for each of the five rounds, the submission may not use information from future rounds (if all information is given at once) in judging the current round.

Here is an example of possible input format:

Since the first mission requires two people, and person A is the first mission planner, the only thing input would be two letters in {A,B,C,D,E,F} indicating his selection. Then the votes of each person, in order, would be input. This continues until a mission team is accepted. Then the votes given on the mission would be input, in no/any particular order. The program would then output the letters of the two people it thinks are spies (there are 2 spies in a 6 person game). Here is an example

A B              # A selects A and B for first mission
P P P F F F      # Everyone votes, mission team is not accepted (lacks majority pass)
B F              # B selects B and F for first mission
P P P P P F      # Mission team is accepted (majority pass)
P F              # Mission fails (there is at least one fail vote). Note that the order does not matter here. 

The bot would then output two people, the people it thinks are most likely to be the spies based on all the information it has up to this point.

B F              # Any two person subset is acceptable

Input then continues for the next 4 rounds, until the game is over.


I will write several hundred test cases (from actual games played online). Then each output will be scored in the following way:

  • 1 point for each correctly guessed spy.
  • 1 point for guessing both spies correctly.

The submission's total score will be the sum of all scores on all rounds in all games. The program will never be told who is a spy (unless it is used to self-score and does not factor into the actual guessing) but this information will be available with the test cases for scoring purposes.

Tie break is code golf.

Meta: I think I'm going to remove output after the first round, because very rarely do people ever fail the first mission. So it will likely just be pure chance.

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