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.

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  • Parts of the challenge you found unclear
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4635 Answers 4635

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144 145

What day is it today?

Given a date y4y3y2y1-m2m1-d2d1, output the day in the week w. 0 as Sunday, 1 as Monday, and so on. You can assume the date is valid, and we use the current date rule and leap rule.

Each submission should be written in this specific programming language:

  • A program consists of a mapping from string of digits to digits, and a sequence of instructions.
  • Each instruction has the format: var=[var|dgt],[var|dgt],...,[var|dgt], which assigns the value of looking up the string constructed by concatenating the values of the right hand side elements ([var|dgt],[var|dgt],...,[var|dgt]) together in the table and put it into the var on the left.

A program is valid if:

  • None of the lookup step fails for all valid input date.
  • Given any valid date in the format mentioned above (initially assigned to the 8 variables y4 y3 y2 y1 m2 m1 d2 d1), after the program is run, the correct result is assigned to the variable w.

You can create as many variables as you like(though bounded by amount of instructions), each variable only containing a digit.

Solution win if there's no strictly better solution, aka. no solution that take less or same amount of items in mapping table, less or same amount of instrucions, and at least one of amounts of items and instructions is less.

For example, this is a solution that wins:

3652425 items 1 instruction

003000101 -> 6
003000102 -> 0
003000103 -> 1
993991231 -> 5

Here, the 3 on 3rd position can be used without any extra cost. This can be used to create multiple mappings, and sometimes save elements when there are more mapping instructions.

A checker is provided here.

  • \$\begingroup\$ I completely don't understand the entire You can have a mapping table and some instructions, each instruction write var=[var|dgt],[var|dgt],...,[var|dgt], meaning search the element [var|dgt],[var|dgt],...,[var|dgt]from table and put i into the var on the left. Failure on searching is not allowed. You can create as many variables as you like(though bounded by amount of instructions), each variable only containing a digit. part. \$\endgroup\$ Jun 15, 2020 at 8:32
  • \$\begingroup\$ I'm very confused about this. Are you sure you're not making assumptions about language features? \$\endgroup\$
    – Adám
    Jun 15, 2020 at 8:32
  • \$\begingroup\$ @Adám I'm requiring using only this language \$\endgroup\$
    – l4m2
    Jun 15, 2020 at 8:40
  • \$\begingroup\$ @mypronounismonicareinstate That mainly mean the only operation is lookup, there's nothing like plus, multiply or whatever \$\endgroup\$
    – l4m2
    Jun 15, 2020 at 8:41
  • \$\begingroup\$ @l4m2 I still do not understand a word. The whole proposal definitely requires a serious rewrite. \$\endgroup\$ Jun 15, 2020 at 8:42
  • 2
    \$\begingroup\$ @mypronounismonicareinstate If it hadn't needed some more time it isn't here \$\endgroup\$
    – l4m2
    Jun 15, 2020 at 8:45
  • \$\begingroup\$ "Solution win if there's no strictly better solution" is not a valid winning criterion because it allows multiple winners. \$\endgroup\$
    – Bubbler
    Jun 15, 2020 at 9:23
  • \$\begingroup\$ @Bubbler Multiple winners is common \$\endgroup\$
    – l4m2
    Jun 15, 2020 at 9:34
  • \$\begingroup\$ @l4m2 Do you mean something like ties in code golf? IMO, code golf ties are fine because they can be seen as equally good, while your criterion is not because it allows potentially multiple answers that can't be compared to each other at all. \$\endgroup\$
    – Bubbler
    Jun 15, 2020 at 9:44
  • \$\begingroup\$ @Bubbler I mean like multiple languages each only comparing to self \$\endgroup\$
    – l4m2
    Jun 15, 2020 at 9:50
  • \$\begingroup\$ @l4m2 The winning criterion is the guide to optimize one's solution in one direction. "Shortest solution in each language wins" does not harm this spirit. Yours don't give which one to optimize for: mapping table size or instruction size? \$\endgroup\$
    – Bubbler
    Jun 15, 2020 at 10:05
  • \$\begingroup\$ @Bubbler Your link claims you wrong \$\endgroup\$
    – l4m2
    Jun 15, 2020 at 11:59
  • \$\begingroup\$ @l4m2 OK, let me say it in a different way. You already showed a "winning" solution with minimal instructions. Then there will be a "winning" solution with minimal table, and then there can be thousands of "winning" solutions in between. Given any "winning" solution, one can tweak a little to get another "winning" solution. Do you really think it is fun? \$\endgroup\$
    – Bubbler
    Jun 15, 2020 at 23:02
  • \$\begingroup\$ @Bubbler Yea an exact bound of table size for each instruction count, if exist, makes its sense \$\endgroup\$
    – l4m2
    Jun 16, 2020 at 5:06
  • \$\begingroup\$ @Bubbler You don't like to see lots of winners because you think "win" is a big issue? \$\endgroup\$
    – l4m2
    Jun 16, 2020 at 5:06

Natural Language Identification Using Only Regular Expressions

For example:

const regex = /English(?=\w+ Hello World)|Spanish(?= Hola Mundo)/;

console.log('EnglishSpanish Hello World'.match(regex)); // English
console.log('EnglishSpanish Hola Mundo'.match(regex)); // Spanish

These wordlists are to be used, and words are to be rewritten entirely using the ASCII characters A-Z and a-z. Languages which use characters that cannot be easily transcribed into ASCII without special knowledge or firsthand experience in that language, are excluded.

For instance, the Albanian word is easily transcribed without special knowledge as te, so Albanian is allowed.

But the Arabic word من cannot be, so Arabic is excluded.

The regular expression must match the language exactly, so appending a list of all languages you are testing before each word is allowed. But however you organize this list, it must be the same for every word you test. See the example above for clarification.

Sandbox Questions

Ideally, brevity of regex, accuracy of language identification, and number of languages taken into account by the regex should all be considered when determining the winner. But I have not decided on that yet, and am very open to suggestions.

In fact this is my first sandbox post and I hope someone can help me format this properly with good rules so that it makes for an interesting and fun challenge. I got this idea from some other contest somewhere where the goal was to identify languages with at least 60% accuracy. But I can't find it anymore.

  • \$\begingroup\$ So only regex submissions are allowed? \$\endgroup\$
    Jul 22, 2020 at 6:02
  • 1
    \$\begingroup\$ Although there are options to "weight" the 3 scores differently, the easiest way is to require the other two scores to be larger than some limit (say, at least 2 languages and at least 60%) then compete for the shortest regex. \$\endgroup\$
    Jul 22, 2020 at 6:04
  • \$\begingroup\$ Also, are there any similar challenge before? \$\endgroup\$
    Jul 22, 2020 at 6:05
  • \$\begingroup\$ Yes, only regex is allowed. A very similar challenge I've found is this: codegolf.stackexchange.com/questions/49596/… \$\endgroup\$
    – GirkovArpa
    Jul 22, 2020 at 6:26
  • \$\begingroup\$ Also this one, which is linked in the other: codegolf.stackexchange.com/questions/42206/… \$\endgroup\$
    – GirkovArpa
    Jul 22, 2020 at 6:27
  • \$\begingroup\$ Pretty similar. But the huge size of the word list will make the solutions different. \$\endgroup\$
    Jul 22, 2020 at 6:33
  • \$\begingroup\$ you should specify a particular flavor of regex. \$\endgroup\$
    Jul 22, 2020 at 6:34
  • 1
    \$\begingroup\$ I would have said JavaScript but I thought there could be a winner for each programming language? \$\endgroup\$
    – GirkovArpa
    Jul 22, 2020 at 6:35
  • 1
    \$\begingroup\$ If you decide to restrict to 2 languages, you may ask for a regex that matches words from list 1 and not match words from list 2. (it may (do anything|never matches) the words that are not in lists) \$\endgroup\$
    Jul 22, 2020 at 6:37
  • \$\begingroup\$ Good idea, I'll do that. \$\endgroup\$
    – GirkovArpa
    Jul 22, 2020 at 6:39

Rage Against the Dying of the Light


"Do not go gentle into that good night" is the title of a poem by 20th century English poet Dylan Thomas. If you've heard it before it was probably because you watched Interstellar, where it was quoted multiple times.


Your program (or function), if it chooses to not go gently, should take no input and print the following text, with an optional trailing newline:

Do not go gentle into that good night,
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.

Though wise men at their end know dark is right,
Because their words had forked no lightning they
Do not go gentle into that good night.

Good men, the last wave by, crying how bright
Their frail deeds might have danced in a green bay,
Rage, rage against the dying of the light.

Wild men who caught and sang the sun in flight,
And learn, too late, they grieved it on its way,
Do not go gentle into that good night.

Grave men, near death, who see with blinding sight
Blind eyes could blaze like meteors and be gay,
Rage, rage against the dying of the light.

And you, my father, there on the sad height,
Curse, bless, me now with your fierce tears, I pray.
Do not go gentle into that good night.
Rage, rage against the dying of the light.

This is , so smallest code in bytes wins.


  • Is this too bland/simple of a challenge? There's a lot of potential for compressing the poem, but it's not really complex.
  • 1
    \$\begingroup\$ Just be careful it isn't marked as a duplicate of this \$\endgroup\$
    – lyxal
    Aug 15, 2020 at 3:09
  • 1
    \$\begingroup\$ Is the string being different not enough? \$\endgroup\$
    – nope
    Aug 15, 2020 at 12:31
  • \$\begingroup\$ I hope this one is different enough. Things like this are usually borderline since there are several lyrics question closed but some are still open. \$\endgroup\$ Aug 15, 2020 at 14:51
  • 1
    \$\begingroup\$ Despite some interesting repetition in this poem, I think the text compression methods used would be the same, making it a duplicate. \$\endgroup\$
    – xnor
    Aug 16, 2020 at 6:52

Anti-codegolf, unique characters


Write a program/method whose source code's characters are unique. You shall put as many characters as you can.


There is no input.

Valid characters

All characters are identified by their Unicode code point. The following characters are invalid, and shall not appear in the source code nor the output:

  • C0 and C1 control characters (U+0000 – U+001F and U+0080 – U+009F) except Character Tabulation (U+0009), Line Feed (U+000A), Line Tabulation (U+000B), Form Feed (U+000C), Carriage Return (U+000D), and Next Line (U+0085)

    • Outputting these characters are banned, even if they have special effect on an output stream.
  • Low and High surrogates (U+D800 – U+DFFF)

  • Noncharacters (U+FDD0 – U+FDEF, and U+xxFFFE and U+xxFFFF for xx = 00 – 10)

  • Code points that are outside of U+0000 – U+10FFFF

A character is valid otherwise. In particular, whitespaces, combining characters, and private uses, and even reserved characters are valid.

Restrictions and output

Your program shall halt.

The output shall be a string. This includes string returned by a function, or string printed to stdout, stderr, a file, or a dialog box.

The set of the characters in the source code shall be a subset of the set of the characters in the output. Note that the output doesn't need to consist of unique characters.

The output may be arbitrarily many strings, for which their concateration will be considered for the restriction above.


This is an anti-codegolf. The submission with the longest source code wins.

  • \$\begingroup\$ Can we output though an error message? \$\endgroup\$
    – Adám
    Aug 24, 2020 at 4:37
  • \$\begingroup\$ @Adám I'd permit it. \$\endgroup\$ Aug 24, 2020 at 4:45
  • 1
    \$\begingroup\$ Explicitly stating the range of valid codepoints would be useful. \$\endgroup\$
    – Bubbler
    Aug 24, 2020 at 4:45
  • \$\begingroup\$ So then any expression that generates an error message containing the offending line, followed by a comment symbol and all the unneeded characters, would be the perfect solution? \$\endgroup\$
    – Adám
    Aug 24, 2020 at 4:47
  • \$\begingroup\$ @Adám Welp. Then I should add a restriction. \$\endgroup\$ Aug 24, 2020 at 4:48
  • \$\begingroup\$ Be careful about that restriction. Putting restrictions on code is notoriously difficult to get right. \$\endgroup\$
    – Adám
    Aug 24, 2020 at 4:49
  • \$\begingroup\$ Also, the languages whose inline comment starts with single char (say Python's # or APL's ), or any esolangs that ignore non-commands will likely get perfect score on any task solvable in that language. \$\endgroup\$
    – Bubbler
    Aug 24, 2020 at 4:53
  • \$\begingroup\$ Not only that, many languages could probably just use an unfinished string (i.e. missing the closing quote) containing all the other necessary characters. \$\endgroup\$
    – Adám
    Aug 24, 2020 at 5:05
  • \$\begingroup\$ @Adám What about now? \$\endgroup\$ Aug 24, 2020 at 5:08
  • \$\begingroup\$ Did you intentionally remove the requirement that the output be longer than the input? \$\endgroup\$
    – Adám
    Aug 24, 2020 at 5:10
  • \$\begingroup\$ What are "Reserved characters"? \$\endgroup\$
    – Adám
    Aug 24, 2020 at 5:10
  • \$\begingroup\$ @Adám Yes. I tried to find a better restriction. \$\endgroup\$ Aug 24, 2020 at 5:10
  • \$\begingroup\$ @Adám Reserved characters are code points that are not assigned a unicode character. \$\endgroup\$ Aug 24, 2020 at 5:11
  • 1
    \$\begingroup\$ You've now banned line breaks. Lots of languages will have problems using only one-liners. \$\endgroup\$
    – Adám
    Aug 24, 2020 at 5:29
  • 4
    \$\begingroup\$ [code-bowling]. \$\endgroup\$
    Aug 24, 2020 at 5:36

Gray codegolf

The gray code is a binary numeral system such that two successive values differ in only one bit.

Decimal Binary  Gray
0       0000    0000
1       0001    0001
2       0010    0011
3       0011    0010
4       0100    0110
5       0101    0111
6       0110    0101
7       0111    0100
8       1000    1100
9       1001    1101
10      1010    1111
11      1011    1110
12      1100    1010
13      1101    1011
14      1110    1001
15      1111    1000


Print the first k Gray code numbers, starting from 0. The shortest code wins!

You may choose the output format as long as it's human-readable.

Similar questions

  • \$\begingroup\$ Why the strict output format, and why the arbitrary constant limit of 1000 (not taking an input number)? Also, possible dupe. \$\endgroup\$
    – Bubbler
    Aug 28, 2020 at 4:19
  • \$\begingroup\$ When you say first 1000, is that decimal or binary? \$\endgroup\$
    – Jo King Mod
    Aug 28, 2020 at 7:55
  • \$\begingroup\$ The challenge I linked is code golf. \$\endgroup\$
    – Bubbler
    Aug 28, 2020 at 16:06
  • \$\begingroup\$ @Bubbler nvm, it looks like I am banned from posting lol \$\endgroup\$ Aug 28, 2020 at 17:35
  • \$\begingroup\$ printing a sequence and finding a number in a sequence tend to be very similar tasks. \$\endgroup\$
    – Razetime
    Sep 1, 2020 at 3:28


Somewhat famously, 'B' + 'a' + + 'a' + 'a' returns BaNaNa in Javascript. You goal is to output precisely BaNaNa. However, to keep it more in the style of the original Javascript, you may not use:

  • The bytes 78 or 110
  • Whatever n or N are encoded as if your language uses a special encoding, or
  • Any string literal containing the characters n or N

in your source code.

As a special note, I'd like your feedback as to if restricting numeric literals equal to 78 and 110 would be any good.

Additionally, this is my first question, and I'm aware that 'Do X without Y' is officially not super popular these days, but I frankly quite enjoy them, so I have no idea if this will be well-received or not. I'm hoping that the reference to the JS quirk is enough to make it interesting.

  • 1
    \$\begingroup\$ Restricting numeric literals would just result in 77+1 or +"78" or whatever trivial workarounds, so I don't particularly think it's a good idea. For the challenge itself, I don't know if it'll be well-received either. (For the record, BaNaNa = Barium Sodium Sodium = atomic number 56 11 11.) \$\endgroup\$
    – Bubbler
    Sep 7, 2020 at 3:37
  • \$\begingroup\$ Since this is such a short string composed only of letters, it's very, very simple to work around it. You need a better restriction method. See this, and the questions in restricted-source \$\endgroup\$
    – Razetime
    Sep 7, 2020 at 4:24
  • 1
    \$\begingroup\$ Indexing into custom character sets will make this trivial. \$\endgroup\$
    – Adám
    Sep 7, 2020 at 5:03
  • 2
    \$\begingroup\$ JS, 11 bytes: `Ba${+"a"}a` \$\endgroup\$ Sep 7, 2020 at 14:44

Find the nth positive integer m for which \$\tan(m) > m\$


Write a program/function that when given an integer \$n\$ as input outputs the \$n\$th positive integer \$m\$ for which \$\tan(m) \gt m\$.

Note: \$m\$ is in radians


This is so shortest bytes wins.

Sample Testcases

# n -> m
1   -> 1
2   -> 260515
3   -> 37362253
5   -> 534483448
9   -> 214112296674652
10  -> 642336890023956
16  -> 4285797387061825747646013

Find more at A249836

Inspired by What is the biggest tangent of a prime?

  • \$\begingroup\$ +1 for referencing a MegaFavNumbers video. \$\endgroup\$
    – Razetime
    Aug 20, 2020 at 3:24
  • 4
    \$\begingroup\$ I don't understand the point. Are you asking us to find the nth number such that tan(x) > x? Is there any approach that will be shorter than iterating over all numbers until you find the nth number such that tan(x) > x? \$\endgroup\$ Aug 20, 2020 at 3:33
  • 1
    \$\begingroup\$ Where is n in the equation? I'm lost. \$\endgroup\$ Aug 20, 2020 at 9:07
  • 2
    \$\begingroup\$ @Razetime On the channel Stand-up Maths, right? \$\endgroup\$
    – Rosie F
    Aug 20, 2020 at 18:49
  • 1
    \$\begingroup\$ replace "nth" with "first" "second" etc -> "first/second/etc number m for which ..." i.e. n is not in the equation @V.Courtois \$\endgroup\$
    – golf69
    Aug 20, 2020 at 20:30
  • 1
    \$\begingroup\$ @Mukundan314 maybe indicate that n is the input? \$\endgroup\$
    – golf69
    Aug 20, 2020 at 20:31
  • 1
    \$\begingroup\$ @golf69 oh! So it has to be an integer, not a number. I see now :) And yes, indicating n is the input would be nice. \$\endgroup\$ Aug 21, 2020 at 6:50
  • 6
    \$\begingroup\$ I don't really see this being solved any way that taking the generic golfiest code for "find the n'th number meeting [predicate]", of which there's plenty of challenges, and sticking in tan(m)>m for the predicate. \$\endgroup\$
    – xnor
    Aug 22, 2020 at 7:04
  • 1
    \$\begingroup\$ Solutions relying on floating-point arithmetic will get the wrong answer starting around the 11th term. You’ll need to clarify whether that’s acceptable. \$\endgroup\$ Aug 22, 2020 at 22:14

Is it a Pythagorean triple?

Given three numbers, determine whether they form a primitive Pythagorean triple. Here is the definition:

  • all three numbers are positive integers
  • they represent the side lengths of a right-angled triangle, that is, \$a^2 + b^2 = c^2\$ for any ordering of \$a\$, \$b\$, and \$c\$
  • no other primitive Pythagorean triple exists with the same ratio of side lengths, that is, they are coprime. For example, \$[6, 8, 10]\$ is not a primitive Pythagorean triple, even though it satisfies the above conditions, because the simper \$[3, 4, 5]\$ exists.


  • Unless your language doesn't support them, you must accept floating-point numbers (even though Pythagorean Triples use, by definition, integers)
    • meta: Is this necessary? Is it too restrictive?
  • You may be given negative numbers, \$0\$, or numbers that cannot form any triangle (right-angled or not, i.e. \$a + b \le c\$), in which cases you must return false.
    • meta: Is this necessary? Does it make it too difficult?
  • You can return any two distinct individual values, or any typical truthy/falsey values for your language.
  • Standard I/O and loophole rules apply.
  • This is , so shortest function or full program in bytes wins.

Test Cases

[0, 3, 3] => false
[3, 4, 5] => true
[5, 3, 4] => true
[3, 4, 6] => false
[3, 4, 10] => false
[6, 8, 10] => false
[3.0, 4.0, 5.0] => true
[3.1, 4.0, 5.0] => false
[-3, -4, -5] => false
[3, 4, -5] => false
[4.5, 6, 7.5] => false
[91, 60, 109] => true
[264, 265, 23] => true
[81, 210, 184] => false
[140, 221, 83] => false


  • Are the first two rules necessary, or do they restrict it too much?
  • Is it clear enough? Are there any additional rules I need to add? Are more test cases needed?
  • Does this suit the and tags? It's kind of tangential to both areas.
  • Is this too similar to the existing questions that want you to generate triples?
  • \$\begingroup\$ possible duplicate of this challenge \$\endgroup\$
    – Razetime
    Oct 18, 2020 at 13:38
  • \$\begingroup\$ @Razetime that challenge appeared on the front page today and inspired me to make this one. I thought it was different enough because of the coprime requirement and I added the extra rules about invalid values/floats to make it more interesting as well \$\endgroup\$
    – pxeger
    Oct 18, 2020 at 14:32
  • \$\begingroup\$ Input validation tends to make for a challenge that is less fun. The coprime requirement is nice, but I'm not sure if it completely changes the challenge. \$\endgroup\$
    – Razetime
    Oct 18, 2020 at 15:04
  • 2
    \$\begingroup\$ This seems to me to be too much a combination of two separate generic tasks, checking that a^2+b^2=c^2 when sorted, and that a and b are relatively prime. \$\endgroup\$
    – xnor
    Oct 19, 2020 at 9:40

Am I A Perfect Two Integer?

A “perfect two integer” is an integer that works as x in the following equations:

Let i = integer, j = integer, x = perfect two integer:
2^i = x
j^2 = x

Example “perfect two integers”: 4, 16, 64, 256, 1024 (see a pattern here?)

Your answer should take a number from stdin or an argument. This should be relatively easy, but this is , so the shortest answer wins. (Note: there are ways to simplify these equations that aren’t listed here).

Sandbox Questions:

  1. Is this a duplicate?
  2. Is this too easy?
  3. Any other thoughts?
  • 3
    \$\begingroup\$ My personal feeling is that this is too easy. There's not really much scope for golfing the answer once you find the pattern. \$\endgroup\$
    – Sisyphus
    Oct 28, 2020 at 0:25
  • \$\begingroup\$ Yeah, you're probably right. It's kind of just like if it's a power of 4. I somehow didn't think about this while making the question. \$\endgroup\$
    – nthnchu
    Oct 28, 2020 at 0:34

Undecidable halting set

Write a program such that the set of natural numbers on which it halts is not recursive.

Shorter is better.

You may assume natural numbers in your language are unbounded.

Example: Python 3 (52 chars)

lambda n:eval(n.to_bytes(n.bit_length()//8+1,'big'))
  • \$\begingroup\$ This boils down to "emulate a Turing-complete language", which is the same as eval in any Turing-complete language that supports the feature (as you already showed in the example). I don't think it's an interesting challenge. \$\endgroup\$
    – Bubbler
    Jan 19, 2021 at 6:37
  • \$\begingroup\$ @Bubbler Eval is only half the battle (assuming the language has eval in the first place). You still need to handle the fact that the inputs are natural numbers, not arbitrary strings. That is, you need to surject the natural numbers onto a set of strings sufficient to get the undecidable behavior under eval. \$\endgroup\$
    – user76284
    Jan 19, 2021 at 7:08
  • \$\begingroup\$ @Bubbler I'd consider an eval-free version of the challenge though, if you have any suggestions. Not sure how that restriction is usually phrased/enforced. \$\endgroup\$
    – user76284
    Jan 19, 2021 at 7:09
  • 1
    \$\begingroup\$ Eval is half of the battle, but the other half is converting a natural number to a string, which is just a matter of base conversion (which gives ALL strings, maybe except strings starting with null bytes, which doesn't matter in most languages). Unfortunately, banning built-ins is discouraged, and we already had a challenge about simulating a different Turing-complete language, so I don't think banning eval will make the challenge better. \$\endgroup\$
    – Bubbler
    Jan 19, 2021 at 7:36
  • \$\begingroup\$ @Bubbler Is banning eval not an objective restricted-source criterion, as opposed to “no built-ins”? \$\endgroup\$
    – user76284
    Jan 19, 2021 at 19:28
  • \$\begingroup\$ Banning built-ins means banning a specific feature of a language, like some old challenge banned exponentiation. It is different from restricted source, which is about restrictions in the source code as text, not looking at the features it uses. There are various classes of eval, e.g. interpret the whole language (Python's exec), interpret the subset of the language (Python's eval and ast.literal_eval), interpret a different language (you can't even count how many Turing-complete mini languages are out there; if Perl regex is Turing-complete, would you ban it?), etc. \$\endgroup\$
    – Bubbler
    Jan 21, 2021 at 0:53

Here is the problem, for which I can only think of an iterative solution and have not found a closed formula.

This problem was found on : https://www.codingame.com/ in the shortest codemode.

You need to paint a house with R rooms.

For each room there are four walls and one ceiling, which all have the same dimensions and need C coats of paint.

You can't paint the next coat until the previous one has dried. You're finished when every wall is dry. Time taken to move between walls, ceilings, rooms is negligible.

It takes you M1 minutes to paint each coat, and M2 minutes for the paint to dry on each. You must finish in the least possible time, otherwise they will not pay you.


In :

Line 1: R, C, M1, M2 separated by spaces.
R: Number of rooms in the house
C: Coats of paint needed for each wall/ceiling
M1: Minutes taken to paint each coat
M2: Minutes taken for paint to dry on each coat (measured from when you've finished the entire coat)

Out :

The time taken to paint the entire house in the format H:MM


1 ≤ R ≤ 10
1 ≤ C ≤ 20
1 ≤ M1 ≤ 10000
1 ≤ M2 ≤ 10000


input: 1 1 12 0

output: 60

input: 5 2 5 30

output: 280

input: 1 5 5 200

output: 1045

  • 4
    \$\begingroup\$ Is this a problem from another site? If so, you need to state where the problem comes from. Also, unlike other online judge sites, we tend to allow submissions to be functions or full programs, and allow a wide range of I/O methods for both. Having to convert the minutes to hours/minutes and format as h:mm is not so related to the core (and requiring such formatting is discouraged on our site), so I suggest to simply output a number in minutes. \$\endgroup\$
    – Bubbler
    Jan 28, 2021 at 0:16
  • \$\begingroup\$ @Bubbler I have taken your remarks into consideration. I hope it's what you expected. \$\endgroup\$ Jan 28, 2021 at 9:31
  • 3
    \$\begingroup\$ Do you have permission to repost this challenge? CodinGame's rules state (Article 9): 'The reproduction, representation or use of all or part of the components proposed in the CodinGame Contests is strictly prohibited.' \$\endgroup\$
    – Dingus
    Jan 28, 2021 at 12:15
  • 2
    \$\begingroup\$ Posting a challenge from elsewhere so that you can be shown an answer is engaging with this community in bad faith. You can ask for programming help in places such as SO, but this isn't intended to be one of them. \$\endgroup\$
    – xnor
    Jan 28, 2021 at 17:05
  • \$\begingroup\$ @xnor I am not acting in bad faith or such. I found this problem interesting and I wanted to share with the community to find an optimal answser. There is nothing for me it this except extending my own knowledge as well as community knowledge \$\endgroup\$ Jan 29, 2021 at 9:00

Hello World! - Generation 3392

Your job is to create a genetic algorithm that slowly evolves and mutates its string until the output is equivalent to "Hello World!".

The genetic algorithm should start with a random string generated, and continue for generations, making random mutations to its code, like this:

Gen 3393 - Hemmo World!


Gen 3394 - Hemko World!

Heres how the randomization algorithm works:

  1. Create a function named randint(n), import the time module.
# Written in Python 3.8
import time # imports time
def randint(n): # create function
  1. Get the current time since Jan 1. 1970, multiply by n and assign it as var "t". Make t an integer not a float.
t=int(time.time()*n) # Set time, and multiply by n.
  1. Use the "%" operation on var "t" (var t is the first argument), with var n as the second argument, assign it as "rand". Code in python should look like this:
rand=t%n #setup a psuedorandom number, since you already have a counter, use n as the limit number, and reset the counter once the counter reaches the limit number. This generates a psuedorandom number within n.
  1. Return rand.
return int(rand) #return results as integer.

Your program should have:

  • A randomized start string (using the rand_int algorithm)
  • A point it reaches "Hello World!"
  • Mutation, using "parents". You are not allowed to completely change a string, only modify 1 character each generation.
  • Mutations are not allowed to be repeated twice/No mutation backtracking.
  • Once a genetic algorithm has a correct letter in its correct position (such as "e" in "reJ" and "Hes"). It is forced to stay as that letter in that position and the genetic algorithm is forced with that string forever, this repeats for all other positions. This way the time increases additionally instead of exponentially. So you cannot do this: ["Hlllr" -> "Hellr" -> "Hfllr"]

So I can do this:

Herlo Wcrld
Herlo Wrrld

But you cannot change >1 character/byte at a time:

Herto Wcrld
Heflo World

You can do whatever else you want with it if it satisfies those requirements.


This is , so the answer with the least amount of bytes wins.

  • \$\begingroup\$ For code golf to work, the rules must be very clearly defined. At the current state people will do do (s:=randomString()); while(s!="Hello world!"); print(s); (pseudocode): (you can make this a popularity contest, but that's even harder to get right. I don't know why) \$\endgroup\$
    Feb 6, 2021 at 13:46
  • \$\begingroup\$ @user202729 I want the person to make a genetic algorithm, where it starts with a random string. mutates the previous string randomly by 1 character during each generation, and eventually outputs "Hello World!" \$\endgroup\$
    – fr4cew
    Feb 6, 2021 at 13:55
  • 3
    \$\begingroup\$ Besides being poorly-defined, it is also an non-observable behavior. \$\endgroup\$
    Feb 6, 2021 at 14:02
  • \$\begingroup\$ No, (hey, that's a link. Read it.) \$\endgroup\$
    Feb 6, 2021 at 14:09
  • \$\begingroup\$ Wait, that's not what I mean. I'll explain it later. \$\endgroup\$
    Feb 6, 2021 at 14:47
  • \$\begingroup\$ @user202729 Right... \$\endgroup\$
    – fr4cew
    Feb 6, 2021 at 14:53
  • \$\begingroup\$ But if the mutations between generations are random, there's no guarantee that the program will ever generate a specific string. You have to add a constraint like "the program should not generate a given string twice" \$\endgroup\$
    – anotherOne
    Feb 6, 2021 at 17:11
  • \$\begingroup\$ @Davide I think that rule already existed in the "A point it reaches 'Hello World!'" but I'll add that anyway. \$\endgroup\$
    – fr4cew
    Feb 6, 2021 at 19:26
  • \$\begingroup\$ A few things that I find missing from the rules: How long is the string? How do you mutate space/punctuation marks? I agree that is has non-observable behavior, because you can't see it mutating the string. Does the code have to be in python? Why should it randomize its input and why should it be random during the process? Wouldn't it be better if you get a string from user input (defined length) and then transform it to "Hello World!" (because that would allow bf and other languages to work) \$\endgroup\$
    – Deadbeef
    Feb 7, 2021 at 6:37
  • \$\begingroup\$ @Deadbeef 1. The length of hello world, 2. It works with base 64, 3. No, 4. Because I liked it that way. 5. I do not know. \$\endgroup\$
    – fr4cew
    Feb 7, 2021 at 15:22
  • \$\begingroup\$ Okay, about the unobservable behavior, what I mean is... \$\endgroup\$
    Feb 7, 2021 at 15:59
  • \$\begingroup\$ It's relatively hard to define what exactly "having a string stored internally" means (what if the string is stored as a list of int values (char codes)? What about encoded in the exponent like in FRACTRAN?) Instead, you can require the programs to output the generations (i.e., print the random strings, each subsequent string has one character changed, etc.) [please review other sandbox posts] \$\endgroup\$
    Feb 7, 2021 at 16:02

Return all elements around an index forming sun

Define a function that takes in a 2D array and a 2D index, and return all the elements of the 2D array that are directly vertical to, horizontal to, and diagonal to the given index, and the returned list must omit the index itself.

External modules, like numpy, as allowed. The most efficient program wins.

enter image description here

  • \$\begingroup\$ ... while we do have [fastest-code] on this site, there are specific requirements; restricting allowed programming languages is another problematic thing; \$\endgroup\$
    Feb 8, 2021 at 14:38
  • \$\begingroup\$ besides, this definitely sounds like that you're outsourcing your homework to this site. \$\endgroup\$
    Feb 8, 2021 at 14:38
  • \$\begingroup\$ @user202729 I already have a numpy solution... this is definitely not homework XD \$\endgroup\$ Feb 8, 2021 at 15:34
  • \$\begingroup\$ @user202729 Okay, removed language restriction. \$\endgroup\$ Feb 8, 2021 at 15:35
  • \$\begingroup\$ Okay, the other problem is with "most efficient code win". Code golf is popular around here because it's easy to measure, but with this you have to install all sort of weird programming languages on a test machine. \$\endgroup\$
    Feb 9, 2021 at 2:07
  • 2
    \$\begingroup\$ I don't think this is very interesting to do fastest code anyway, because it can be done in linear time anyway (with the array given); besides the general consensus is to allow "full program or function" [please review other sandbox posts] \$\endgroup\$
    Feb 9, 2021 at 2:11
  • \$\begingroup\$ @user202729 Okey. \$\endgroup\$ Feb 9, 2021 at 2:27

Create a Screw

There are a variety of code cad languages, as well as other 3d API's that allow you to define shapes with code. Some of these are limited, while others are Turing complete and/or use a popular programming language such as Python or JavaScript.

The Challenge

Output a 3d model of a screw. Acceptable formats include .stl files and .obj files. A screw is defined as a shorter, wider cylinder on top of a taller, thinner cylinder, which should be threaded at least 5 times. Winner is whoever has the shortest code by two weeks after this question is posted. Standard rules and loopholes apply, with the exception that anything that allows you to programmatically define a 3d object is treated as a program language.


Should I add a spot for the screw driver to my definition of a screw? On the one hand, that would be more realistic, but on the other, it might just add bloat to answers, since I don't think there's anything interesting you can do with it.

I plan to include an example of a minimal screw under whatever definition I end up using, with pictures and outputs in every allowed format.

For the purpose of sorting and answer headers, should each langauge/framework combo be treated as a separate language? I'm leaning towards this, since It would be cool to have an easily searchable set of code for a bunch of different frameworks.

  • 1
    \$\begingroup\$ While the challenge is probably clearly defined enough, it might not allow solutions more interesting than hardcoding compressed output. \$\endgroup\$
    Feb 15, 2021 at 2:04
  • \$\begingroup\$ How could I make sure that it does without fundamentally changing it? Or do you think that's not possible? I feel like there might be some potential for interesting ways of doing the threading, but I haven't used very many of these languages.. \$\endgroup\$
    – import huh
    Feb 15, 2021 at 2:40
  • \$\begingroup\$ No idea... I think that (1) if there's a lot of boilerplate in the file format, using a library might be shorter (2) if the structure of the output file is not very repetitive, computing the coordinates might be shorter than hard coding + compressing it. I'm not familiar with either file format so I can't tell. -- -- nevertheless the challenge is on-topic; what I've said only concerns whether it's interesting [please review other sandbox posts] \$\endgroup\$
    Feb 15, 2021 at 2:46
  • \$\begingroup\$ I think both formats basically just contain the points for every triangle used to represent the 3d object. To be honest I didn't really think about directly creating the file. Compared to using a library, it seems incredibly inefficient. That could make for an interesting challenge on it's own, though... \$\endgroup\$
    – import huh
    Feb 15, 2021 at 2:58
  • \$\begingroup\$ You should probably add a specific diagram with the proportions for the screw, or maybe ask the program to take it as input \$\endgroup\$
    – Razetime
    Feb 15, 2021 at 2:58
  • \$\begingroup\$ @Razetime There's no specific proportion, just "larger" and "smaller". \$\endgroup\$
    Feb 15, 2021 at 3:06

Print your PPCG avatar

This is a graphical output question.

You have to connect to the codegolf.stackexchange.com in your homepage, scrape and download your avatar and show it in your default image viewer or some other way.

Standard loopholes apply, connections only allowed to codegolf.stackexchange.com

One language can be only used once, but a user can post multiple answers in different language

Tags: ,,

  • 3
    \$\begingroup\$ This is probably a dupe of this. Finding the avatar instead of the id wouldn't affect most of the code. Your final line is odd, do you mean that if I answered in a language it would prevent anyone else from using that language? That seems like a bad rule - what if I started on my answer and someone posted while I was working? I can't see any benefit, but perhaps I am not understanding. \$\endgroup\$ Feb 20, 2021 at 18:10
  • \$\begingroup\$ I think it would be interesting if you have to print the ascii representation of the user before you , without scraping. With a standard way to produce the ascii image so people can't differ. i.e. img to ascii \$\endgroup\$
    – Alex bries
    Feb 20, 2021 at 21:13

See who can write the longest code in order to print "Hello World!". The rule is that if you remove any single character from the code, it should NOT run.

  • \$\begingroup\$ I think we have a similar challenge already. It's pretty easy to get an infinite score with these rules. \$\endgroup\$ Feb 25, 2021 at 1:23
  • 3
    \$\begingroup\$ It is a weaker version of Programming in a Pristine World and a different variant of Biggest Irreducible Hello World. But note that, in many languages, it is possible to add arbitrarily long no-op code that breaks when exactly one char is removed. For example, Python's ''+''+''+... causes syntax error when any of ' or + or a newline surrounding it is removed. \$\endgroup\$
    – Bubbler
    Feb 25, 2021 at 1:41

Output function from one to another

I tried to post this twice and I gained negative feedback, so I will put what I have in mind here if anyone is interested.

Get a certain output function from one programming language and transfer to another. You'll be recreating an output function that came from a different programming language. There is a certain criteria in order for the answer to be valid:

  1. It should function the same way as the original function. All things that function can do should be applied to the recreated one. For example, Python's print() has certain keywords like end.
  2. Syntax doesn't matter. Example, if you can't use the << for cout, don't use it. Use what's available.
  3. The function should be able to output the same errors like the original. Replicate the same errors from the original function. If impossible, leave it out.

An answer example would be making printf() from C using Python or making Console.WriteLine() (or just WriteLine() if incapable) from C# using Ruby. Any output functions that are already similar to 2 languages don't need to be replicated in any of them.

  • 1
    \$\begingroup\$ "Get a certain output function from one programming language and transfer to another." To clarify, is the challenge to write source code which works in two different languages and does the same thing? What's the winning condition because this sounds very trivial. For example, print does the same thing in many languages. \$\endgroup\$
    – 79037662
    Feb 24, 2021 at 20:25
  • 2
    \$\begingroup\$ Actually that doesn't mesh with "syntax doesn't matter". The point of this challenge is completely unclear, could you please clarify it? \$\endgroup\$
    – 79037662
    Feb 24, 2021 at 20:26
  • 1
    \$\begingroup\$ I see you edited this post but the point of the challenge is still completely unclear. What exactly would a valid submission look like? \$\endgroup\$
    – 79037662
    Feb 25, 2021 at 20:56
  • \$\begingroup\$ I don't really get the point of this task. Sure, someone could write code that does this, it might take some work to get exactly right, but is there a challenge underneath it? Is it code golf? \$\endgroup\$
    – xnor
    Feb 26, 2021 at 3:08
  • \$\begingroup\$ @xnor It isn't code golf, nor king of the hill. It's an ordinary coding challenge if they can replicate a function from one language to another. \$\endgroup\$ Feb 26, 2021 at 5:53
  • 1
    \$\begingroup\$ @MarkGiraffe That's not really a thing on this site -- challenges need to have an objective winning criterion. From the close reason: "Questions without an objective primary winning criterion are off-topic, as they make it impossible to indisputably decide which entry should win." \$\endgroup\$
    – xnor
    Feb 26, 2021 at 8:13

Random Roman Numerals

Printing a random number is easy, but what about roman numerals? Your task is to output a random roman numeral from 1 to 1000, both inclusive.


  • Each number has to have the same chance of appearing
  • The program should use the language's random module or other random algorithm

Remember, I is 1, II is 2, III is 3. V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. Also note that IV is 4, IX is 9, XL is 40, XC is 90, CD is 400, and CM is 900. For more information see the Wikipedia page.

This challenge is , so try to have the shortest program possible!

  • \$\begingroup\$ I'd really recommend loosening the restrictions for the random numbers. What if the language's random module doesn't guarantee exactly equal chances? Can we assume it does? What about an implementation of an algorithm typically used by language's random modules, like xorshiro or the mersenne twister? A much better restriction in my opinion would be requiring that every result is possible, and it's unlikely people will deviate too far from a uniform distribution anyway. \$\endgroup\$ Mar 10, 2021 at 5:43
  • 1
    \$\begingroup\$ Sounds like you're combining two or more unrelated core challenges into one ― consider splitting the challenge up into separate challenges ― or dropping unnecessary parts. Just watch out for duplicate challenges: random number generation and Roman numeral conversion are popular tasks. \$\endgroup\$
    – Adám
    Mar 10, 2021 at 6:01

Is this an one-one function?

, , ,

Two sets given as input, one is the domain of a function, and other one is the co-domain of a function. As an example

$$ \{1,2,3,4\} $$ $$ \{5,6,7,8,9\} $$

Now if the range set of the function, i.e. set of each element in the co-domain set which maps to the domain set (1 -> 5, 2 -> 6, ......) is equal to the co-domain set, then it is a one-one function.

For the above example, the range set is

$$ \{5,6,7,8\} $$

So the range set is not equal to co-domain set, the function is not a one-one function.


Inputted two domain and co-domain set of function, output a truthy value if the function is one-one or falsey if not.

Test cases

{1,2,3,4} {5,6,7,8,9} -> Falsey
{a,b,c} {b,c,d} -> Truthy
{4,8,2} {3,4} -> Falsey

Standard loopholes apply, , so shortest code wins

Pre-defining the input sets in the header section of TIO is not allowed.

  • 5
    \$\begingroup\$ Is this challenge simply asking if the two sets have equal length? If not, can you include counterexamples? \$\endgroup\$ Mar 21, 2021 at 18:03
  • \$\begingroup\$ @water_ghosts yes i feel it is like that \$\endgroup\$
    – Wasif
    Mar 22, 2021 at 5:14
  • 1
    \$\begingroup\$ not particularly interesting \$\endgroup\$
    – rak1507
    Mar 22, 2021 at 12:11

Remaking Kernel

I made a program as a final project in the main CS50 Harvard course, and it was named Kernel, written in C alsongside CS50's library.


It has 7 functions: 4 main (talk, count, calculate, build) and 3 advice functions (error, feedback, help).

What each function does:

  • Talk asks for a prompt to the user and outputs the same thing. Talk Function
  • Count asks for a number to count from 1 to there. If the number is bigger than 50, it will lead to an error. Count Function
  • Calculate asks for 2 numbers and an operator (must be either +, -, * or /) then will calculate the value. If the result is a number is greater or equal to 999999999, it leads to an error. However, 0 / 0 = 0 and other division rules still apply. Calculate Function
  • Build asks for a size and something that it can build, which could be either a line, tower, wall, or pyramid. If the size is more than 20, it leads to an error. It would then ask for the character you want to use to build it, then it will be used to build the final product. There are multiple errors here, which is explained at the Error function.
    Build FunctionDisappointed that I can't make a proper pyramid.
  • Error is a library that shows all 14 errors, which is listed in the Error page of this post.
  • Feedback asks for feedback from the user and they can type whatever they want. The input will then be transferred in a new file called Feedback.list.

Feedback Function

Inside Feedback.list: What's in here?

  • Help displays the info of the entire app. Help Function


There are 14 written errors to prevent writing the real errors.

  1. NO_FUNCTION_ADDED: When asking for which function to use, entering a non-existent one will result to this error.
  2. ERROR_CLASS_NONE: In Error, entering a number which doesn't have its error will pop this up.
  3. COUNT_MAX: Well, typing a number greater than 50 won't put up the error, but counting up to 50 will.
  4. INVALID_DIVIDE: Anything divided by 0 in Calculate (except 0 / 0) will put up this error.
  5. ExTREME_VALUE: In Calculate, earning a final number of 999,999,999 or more will result to this error.
  6. OVERSIZE_CHUNK: Entering a size larger than 20 in Build will result to this error.
  7. UNKNOWN_STRUCTURE: Also in Build, inputting a structure unavailable will pop this up.
  8. UNCLEAR_INSTRUCT: If the input for Build's line is not vertical, horizontal or diagonal, they wouldn't know what it is.
  9. OVERWIDTH_COUNT: Building a tower with a width of 20 or more is invalid.
  10. INVALID_PYRAMID: Similar to Build's line, inputting a pyramid unavailable pops this up.
  11. OPERATE_BAD: Inputting an operator unavailable in Calculate is invalid.
  12. MORE_NAMES: If you didn't know, to run Kernel, you need to add your name alongside running it. Me, I use ./Kernel MarkGiraffe. If I use Mark Giraffe instead, it is invalid.
  13. SECRET_USER: Even NOT putting a name is not allowed.
  14. BAD_ALIGNMENT: Not choosing left or right for a diagonal line in Build is invalid.

For this challenge, I want you to remake the program the most designed way, while still keeping low bytes.

In case you are interested, I will post the source code somewhere where you can view it.

  • 5
    \$\begingroup\$ This has LOTS of quality issues. 1) Being a multipart challenge with unrelated subtasks. 2) Rigid I/O (command line arguments AND interactive stdin/stdout AND file output). 3) Input validation and error handling in arbitrary ways. 4) Lack of specification in certain cases. 5) Putting I/O examples in images instead of code blocks. \$\endgroup\$
    – Bubbler
    Mar 23, 2021 at 4:10
  • 2
    \$\begingroup\$ I think the outstanding question is, why would people want to code and golf here? Like, it's cool that you wrote a thing, but it seems like a lot of work for someone to re-do on a recreational programming site without a really compelling reason. \$\endgroup\$
    – xnor
    Mar 26, 2021 at 3:29

Given a program as input. If the program ever output a '1', output a truthy value and halt; if it halts without ever outputting a '1', output a falsy value and halt; if it falls into infinite loop without outputting a '1', fall into infinite loop.

  • \$\begingroup\$ This is unclear, for example: what language will the program be in? Do we take it as a string? And for a turing-complete language, this is impossible (at least if it can take input). \$\endgroup\$
    – Wezl
    Apr 2, 2021 at 15:45
  • \$\begingroup\$ @Wezl Why not?? \$\endgroup\$
    – l4m2
    Apr 2, 2021 at 16:09
  • \$\begingroup\$ You didn't specify the above ^ points, which are important. \$\endgroup\$
    – Wezl
    Apr 2, 2021 at 16:17

Poly-functional Polyglots

I don't have a ton of time to work on this, so I decided to remove it temporarily while I rework the scoring.

  • \$\begingroup\$ I think the scoring system is too convoluted. Optimizing for the bonuses seems like more of a challenge than completing the core task. And if number of languages is the denominator, it’s hard to know how to calculate that upfront. How many shells does echo “Hello World” work in? If I later learn about another one, does that retroactively lower my score? \$\endgroup\$ Apr 2, 2021 at 16:53
  • \$\begingroup\$ @water_ghosts thanks for saying so. I was worried that that would be the case, especially after reading the discussion on things to avoid in questions. I'm going to try and rework this. \$\endgroup\$ Apr 8, 2021 at 19:26

Generate a Printing Program In Some Language


Given some rules:

1: Hello
2: World
4: Code
7: Golf
9: Whatever

Your program should output a program or a function (the output), which should be a valid program (or function) in some language. When the output is run, it should

  1. Ask for some input (i),
  2. Then output the string in the ith index in rules. (If there are none, don't output anything - even an error.)
  3. Return to step 1.



1: Hello
5: World
19: Code

One possible output (python):

while True:
  i = int(input())
  if i == 1:
  if i == 5:
  if i == 19:


Your score is the bytes in your answer (not the output).

Obviously this question should be clarified.

  • \$\begingroup\$ Can we take input as an array of rules (2d, like [[1, "hello"], [2, "weijfiwef"]])? If the index is not in the rules list, can we output an empty string? \$\endgroup\$
    – user100690
    May 16, 2021 at 7:42
  • \$\begingroup\$ Well I thought about that, but some strong-type languages don't allow different types in a same array. If the index is not in the rules list, you can't output anything (as said in step 2). \$\endgroup\$
    – atzlt
    May 16, 2021 at 8:33
  • \$\begingroup\$ Is my output required to be a full program or it is allowed to be a function? \$\endgroup\$
    – tsh
    May 17, 2021 at 7:21
  • \$\begingroup\$ Yes @tsh, can be either full program or function. \$\endgroup\$
    – atzlt
    May 17, 2021 at 14:09
  • \$\begingroup\$ Why downvotes? Could you please explain why? I'll improve \$\endgroup\$
    – atzlt
    May 17, 2021 at 14:19
  • \$\begingroup\$ @SketchySketch Not a downvoter, but it seems to be a boring challenge. \$\endgroup\$
    – Xwtek
    May 20, 2021 at 9:18

Given two reals \$a\$ and \$b\$, output some reals \$r_i\$, such that \$\sum r_i=a\$ and \$\prod\left(r_i+1\right)=b\$. You can assume that it's possible. You can also assume that your float type have infinite precision.

Test cases:

2,3 => 2 or etc.
2,4 => 1,1 or 1/2,(sqrt(57)+9)/12,(9-sqrt(57))/12 or etc.
2,5 => 1/3,1/2,2/3,1/2,0 or etc.
2,8 => sqrt(17)+2,2-sqrt(17),-2 or etc.
2,2 => sqrt(2)+1,1-sqrt(2) or etc.
e,2e => 1,e-1 or etc. (e is natural base, though any number>1 work)
-4,9 => -2,-2 or etc.
0,-1 => sqrt(2),-sqrt(2) or etc.

Shortest code wins.


  • Though I only removed two positives from the existing question, it's a huge change to the result.
  • I decide to keep the assume possible part just to make the note above correct. It can actually be proven that it's always possible.

Breaking BogoBogoSort (In Badness)

The title says it all - make a sorting algorithm with a time complexity of \$O(n!^{n!})\$ or higher in the fewest bytes possible - as far as I can tell, that will require you to make a double exponentiatial formula or worse: that is, \$O(a^{b^n})\$, where \$a, b > 1\$.

Rules (since there must be some)

The list must be returned sorted in a finite time. This can be as high or as low as you want.

The algorithm must work for any real numbers (-30% if you can sort any single type given it's non-mixed).

The algorithm must work of any list length, and must eventually outpace ALL \$O(n!^{n!})\$ formulas, not just BogoBogoSort, and you must state the exact \$O\$ growth rate (for example, \$O(2^{3^n})\$). It may start off slow, but must eventually outpace all other expo-factorial functions (as I now name this growth rate).

Shortest code wins.

  • \$\begingroup\$ What prevents someone from doing a loop just to make it slower (or calculating \$ n!!!! \$, etc.), and then just sorting the array with quicksort? \$\endgroup\$ Jun 5, 2021 at 8:00
  • \$\begingroup\$ Logic. Logic prevents them from doing something that the question didn't mean you to do. Standart loopholes are forbidden by default \$\endgroup\$ Jun 7, 2021 at 8:25

Get the Collatz Sequence

The Challenge

Write a full program or function that, when given an integer \$n \ge 0\$, outputs all steps of the Collatz Sequence (A006577) of \$n\$.

The Collatz Sequence

The Collatz Sequence is defined as: $$ a(n) = \begin{cases} n/2, & \text{if $n$ is even} \\ 3n+1, & \text{if $n$ is odd} \end{cases} \text{while n > 1} $$


Input is some integer \$n \ge 0\$.


Output is the sequence of numbers visited while calculating the Collatz Sequence, while the output is greater than 1.

Additional Rules

Test Cases

n -> sequence
0 -> [0]
1 -> [1]
2 -> [2, 1]
3 -> [3, 10, 5, 16, 8, 4, 2, 1]
4 -> [4, 2, 1]
5 -> [5, 16, 8, 4, 2, 1]
6 -> [6, 3, 10, 5, 16, 8, 4, 2, 1]
7 -> [7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1]
8 -> [8, 4, 2, 1]
9 -> [9, 28, 14, 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1]
10 -> [10, 5, 16, 8, 4, 2, 1]
15 -> [15, 46, 23, 70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1]
20 -> [20, 10, 5, 16, 8, 4, 2, 1]
25 -> [25, 76, 38, 19, 58, 29, 88, 44, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1]
30 -> [30, 15, 46, 23, 70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1]
35 -> [35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1]
40 -> [40, 20, 10, 5, 16, 8, 4, 2, 1]
45 -> [45, 136, 68, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1]
100 -> [100, 50, 25, 76, 38, 19, 58, 29, 88, 44, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1]
9329 -> [9329, 27988, 13994, 6997, 20992, 10496, 5248, 2624, 1312, 656, 328, 164, 82, 41, 124, 62, 31, 94, 47, 142, 71, 214, 107, 322, 161, 484, 242, 121, 364, 182, 91, 274, 137, 412, 206, 103, 310, 155, 466, 233, 700, 350, 175, 526, 263, 790, 395, 1186, 593, 1780, 890, 445, 1336, 668, 334, 167, 502, 251, 754, 377, 1132, 566, 283, 850, 425, 1276, 638, 319, 958, 479, 1438, 719, 2158, 1079, 3238, 1619, 4858, 2429, 7288, 3644, 1822, 911, 2734, 1367, 4102, 2051, 6154, 3077, 9232, 4616, 2308, 1154, 577, 1732, 866, 433, 1300, 650, 325, 976, 488, 244, 122, 61, 184, 92, 46, 23, 70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1]
4637823 -> [4637823, 13913470, 6956735, 20870206, 10435103, 31305310, 15652655, 46957966, 23478983, 70436950, 35218475, 105655426, 52827713, 158483140, 79241570, 39620785, 118862356, 59431178, 29715589, 89146768, 44573384, 22286692, 11143346, 5571673, 16715020, 8357510, 4178755, 12536266, 6268133, 18804400, 9402200, 4701100, 2350550, 1175275, 3525826, 1762913, 5288740, 2644370, 1322185, 3966556, 1983278, 991639, 2974918, 1487459, 4462378, 2231189, 6693568, 3346784, 1673392, 836696, 418348, 209174, 104587, 313762, 156881, 470644, 235322, 117661, 352984, 176492, 88246, 44123, 132370, 66185, 198556, 99278, 49639, 148918, 74459, 223378, 111689, 335068, 167534, 83767, 251302, 125651, 376954, 188477, 565432, 282716, 141358, 70679, 212038, 106019, 318058, 159029, 477088, 238544, 119272, 59636, 29818, 14909, 44728, 22364, 11182, 5591, 16774, 8387, 25162, 12581, 37744, 18872, 9436, 4718, 2359, 7078, 3539, 10618, 5309, 15928, 7964, 3982, 1991, 5974, 2987, 8962, 4481, 13444, 6722, 3361, 10084, 5042, 2521, 7564, 3782, 1891, 5674, 2837, 8512, 4256, 2128, 1064, 532, 266, 133, 400, 200, 100, 50, 25, 76, 38, 19, 58, 29, 88, 44, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1]


For Meta

  • Is it clear?
  • Any corrections?
  • 1
    \$\begingroup\$ I'd consider this a duplicate of the current Collatz challenge, as the only way to find the length is to generate the sequence, so the answers will all be doing the same thing, just without a length call tacked on the end \$\endgroup\$ Jul 31, 2021 at 16:38
  • 1
    \$\begingroup\$ That is what I've always wondered, though, is how we have a length of Collatz challenge but not a Collatz sequence generation challenge \$\endgroup\$
    – bigyihsuan
    Jul 31, 2021 at 19:58
  • 1
    \$\begingroup\$ Because there is no way to determine the length of a Collatz sequence without generating it, so the core of the challenges would be the same - generating the Collatz sequence. \$\endgroup\$ Jul 31, 2021 at 20:00

Shortest common superstring

Your challenge is to find the shortest common superstring (SCS) for a sequence of English words. The SCS for a sequence is the smallest string that contains all the words in the sequence. The words should be passed as a function parameter.

Answers should be posted in the following format:

<Language name>, <Byte count>


This is code-golf, so the answer with the least bytes wins.

Any suggestions?
  • 1
    \$\begingroup\$ I wouldn't suggest using a popularity contest for a task that looks like it can be code-golf. However, this is likely a duplicate. caird will be around in a while with a more length message and a link to a dupe :P \$\endgroup\$
    – user
    Aug 18, 2021 at 18:53
  • 1
    \$\begingroup\$ Welcome to Code Golf, and thank you for using the Sandbox first! Unfortunately, this is a duplicate. \$\endgroup\$ Aug 18, 2021 at 19:03
  • \$\begingroup\$ Ok, well that's fine. \$\endgroup\$ Aug 18, 2021 at 19:04


Tac-Tok-Toe is just like tic-tac-toe, but instead of three in a row, the winning condition is three in a row but each letter is exactly one space apart horizontally, vertically, or diagonally. The win can also go in any direction.

The games

Each team (X and O) will make their own tac-tok-toe AI's. 10000 games will be played.

The moves

AI.PUT_TILE(board: List[List[str]], place: List[int])
    Places a tile at the specified location

AI.DECIDE_MOVE(board: List[List[str]])
    Decides and returns the index the AI wants to move depending on the current board situation.

AI.GET_WINNER(board: List[List[str]])
    Returns the winner of the board.

The board

The starting board looks like this:

 | | 
 | | 
 | | 

(Yes, I know, that indeed is a horrible tac-tok-toe board.) For example, place [0, 0] is in the upper left square, and place [1, 1] is in the middle. If the X AI places an X at [2, 2], the board would now look like this:

 | | 
 | | 
 | |X

An example of a completed grid could look like this:


We see that X has won, so the game should print: "X wins!"

Game files

[Your side]AI.py:

class [Your side]AI:  # Maybe change to something more meaningful?
    def PUT_TILE(board, place):
    def DECIDE_MOVE(board):
    def GET_WINNER(board):


 | | 
 | | 
 | | 


Any suggestions?

  • 1
    \$\begingroup\$ Given that tic-tac-toe is a solved game, you're going to get a lot of near-identical submissions that play perfectly and always end in a draw. Unless you can put some kind of extra spin on tic-tac-toe that makes it more challenging, I'd pick a different game for a KotH. (Maybe one of these variants could work.) \$\endgroup\$
    – DLosc
    Sep 23, 2021 at 19:16
  • \$\begingroup\$ If you want some tips on writing KotHs with interesting gameplay, check out the king-of-the-hill tag wiki! \$\endgroup\$ Sep 23, 2021 at 19:20
  • 1
    \$\begingroup\$ Can you explain the win condition a bit better? How can you have 3 in a row with 1 space between them unless the board is 5x5 or larger? \$\endgroup\$
    – hyper-neutrino Mod
    Sep 23, 2021 at 19:26
  • \$\begingroup\$ It can go in different directions. \$\endgroup\$ Sep 23, 2021 at 19:26

Randombility of number

The aim of golf is to calculate score of how random 10 inputs given by users were. The Criteria is given below.

  • Points Rule
  • 5+(1.1)^n If inputted numbers are not in Arithmetic OR Geometric progression for n cnsecutive terms
  • 5+(1.1)^n if inputted numbers are not strictly increasing or decreasing for n>2
  • 5*n if number is prime number > 100 here n is number of such terms
  • -5-(1.1)^n if number is substring of $\pi$$ (3.1415926535897932384626433) for n>2
  • 5 if difference between largest and smallest input is greater than 1000
  • -5*n for n repeated inputs
  • -5 + ln(log(p)) if number is square or cube of any number beetween -100 and 100 here p is number
  • -5 if any three input ressemble any valid date (dd/mm/yyyy or mm/dd/yyyy) time(hh/mm or mm/hh) format
    • -Additional
  • (1.5)^n if time interval between two inputs is less than 1.5 seconds

Improvements required Score system.

  • 2
    \$\begingroup\$ Can you please clarify your challenge? I don't get even the point of the challenge or how to win. \$\endgroup\$
    – Seggan
    Oct 26, 2021 at 15:05

Secretary Problem - Cops and Robbers

Both threads

(Link to other thread)

The Secretary Problem is a famous problem. In this challenge, it’s a little different:

  1. You need a new secretary that asks for the least salary
  2. You have a lot of applicants that you can interview one at a time, but don’t know how many applicants there are
  3. Each applicant will tell you how much salary they want (they’ll want at least $1 salary, but may all want $5)
  4. Applicants do not ever request the same salary for some weird reason (not sure if they’re robots or eavesdroppers)
  5. After you interview an applicant, you must give an immediate "yes, I accept you" (truthy) or "no, go away" (falsey)
  6. You want the applicant that asks for the lowest salary, so you can stay rich
  7. No applicant ever requests more than 1 million dollars (for obvious reasons)

In the maths world, it’s actually that you want the highest leveled applicant, but I put it this way because who doesn’t want to stay rich

Cops Thread

Your challenge is to write a program that takes two inputs: the previous applicants’ salaries, the current applicant’s salary, and outputs whether to accept the applicant (truthy) or deny him/her (falsey).

The robbers will attempt to find a list of applicants (and the salaries they demand) that forces your program to accept a person with a high salary demand. You need to attempt to make your program only accept the applicant which asks for the LEAST salary (that way you can stay rich)

The answer that (when answered against by a robbers thread - [link]) accepts the person with the least salary wins/gets accepted (i.e. the answer that accepts a $1, if that doesn’t exist, then the answer that accepts a $2, if THAT doesn’t exist ... and so on)

If your answer does not accept any, (up to the last applicant) you automatically get

Robbers thread

Each answer in the cop’s thread is a program that takes two inputs: the previous applicants’ salaries, the current applicant’s salary, and outputs whether to accept the applicant (truthy) or deny him/her (falsey).

Your challenge is to find a program in the cop’ thread (insert link here) and attempt to give it an input such that it accepts a person with a HIGH salary request. Answer that forces an algorithm to accept the highest amount of money gets accepted (i.e. the answer that forces a cop answer to accept a $1000000 salary applicant, if that doesn’t exist, the answer that forces a cop answer to accept a $999999 salary applicant, if THAT doesn’t exist ... and so on)

Put a link cop answer you are attempting to make go broke in your answer.

You must have at least 100 applicants (with at least one applicant that requests <$100)

Both threads (again)

To stop people getting free points, you cannot make a robbers answer for your own cop answer. 1 answer per thread (you can have both a robber answer and a cop answer as long as the robber answer is against a different cop answer)

Sandbox questions

  • Is this too far-fetched?

Somewhat shamelessly stolen Derived from this question

  • \$\begingroup\$ If the cop is forced to accept the last applicant if they haven't previously accepted anyone, isn't having exactly one applicant with a salary of $1m an unbeatable strategy for a robber? \$\endgroup\$
    – Dingus
    Oct 24, 2021 at 3:49
  • \$\begingroup\$ Changed - "at least 100 applicants" and "at least one applicant that requests <$100" \$\endgroup\$
    – W D
    Oct 27, 2021 at 5:27
  • 1
    \$\begingroup\$ The cops can consider only the bound of $100, as at least one robber will be <$100. \$\endgroup\$
    – pajonk
    Oct 27, 2021 at 9:03
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