# Sandbox for Proposed Challenges

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

Sandbox FAQ

## Posting

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.

## Discussion

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

• Parts of the challenge you found unclear
• 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 needs more feedback, but it's been ignored, you can ask for feedback in The Nineteenth Byte. It's not only allowed, but highly recommended!

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

## Other

Search the sandbox / Browse your pending proposals

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".

Get the Sandbox Viewer to view the sandbox more easily!

# Parse a regex

Grep is a wonderful tool. It can find stuff in files, it can help you spell stuff correctly (grep 'whatever' /usr/share/dict/words or wherever that file is), and it can even test if something is a prime number!

However, the first version was implemented back in the golden age, when FORTRAN was respected, Pascal was the language for beginners, and object orientation was just starting out in on its great adventure.

One could argue that modern developers have nowhere near that much talent or skill, what with their flashy "IDEs" and "frameworks". If they would be asked to implement something similar, they would just jump at the nearest library or cloud thingimabob and say "Done!".

At least, that is what some would say.

## Prove them wrong! Golf grep!

Parse a regular expression without calling any built-in functions or operators explicitly meant for this.

## input:

Basically the same as a simple grep: a regular expression as a command line parameter, followed by an optional filename or a dash. If the filename is not present, or it is a dash, read for stdin.

This is the recommended way to do it, but if you can write an adapter (eg: post stuff to a php form for your program via a shell script), then that is OK as well. The adapter does not contribute to your score.

## output

Lines that match the regular expression.

## Notes:

The regex dialect is PCRE (perl compatible). Files use unix line terminators if it is relevant.

• Closely related, but not quite a duplicate. Nov 18 '19 at 20:42
• Why the downvote? Nov 20 '19 at 8:16
• You've likely been downvoted because you "ban built-in functions or operations explicitly meant for this." Consider this post for a lengthy discussion of why this has fallen out of favour. Beyond this being trivial besides parsing regular expressions, it also doesn't actually describe what a regex is or what it means to be PCRE. Challenges need to be self contained! I think your bet is to make a different matching language yourself and ask us to implement grep but with that language instead of regex. Nov 20 '19 at 19:09

# Predict the state of a Minecraft inventory after click events

Minecraft does inventory management over the network by sending packets describing the clicks that a player does. If you're caching these events, it can be non-trivial to predict what state the inventory is in after the clicks

## Challenge

Take an inventory of 9 slots, each with an item and a type. Assume all items can stack up to 64 and that if a slot would be "overfilled" that the cursor will continue holding onto the items. Then, take a list of the slot index, button, and mode variables for the clicks to be done (mode and button are defined at https://wiki.vg/Protocol#Click_Window). Output the inventory afterwards.

## Restrictions/Rules

You may input and output the inventory in any reasonable format. You may take click input in any reasonable format. You may ignore Mode==2, as the player inventory is not implemented correctly enough for this. You may ignore Mode==3 because this is a survival player You may ignore Mode==5 where Button==8, 9, or 10 for the same reason as Mode 3. Dropping the item is a delete. Your player won't pick it back up or anything silly like that. You may assume that input will have valid counts Don't use standard loopholes

## Examples

Input:

[["diamond",64],[],[],[],[],[],[],[],[]]

[
[0, 0, 0]
[0, 0, 1]
]


Output

[[],["diamond",64],[],[],[],[],[],[],[]]


Input:

[["diamond",64],["dirt", 64],[],[],[],[],[],[],[]]

[
[0, 0, 0]
[0, 0, 1]
[0, 0, 2]
]


Output

[[],["diamond",64],["dirt",64],[],[],[],[],[],[]]


Input:

[["diamond",64],[],[],[],[],[],[],[],[]]

[
[0, 0, 0],
[-999, 4, 4],
[0, 4, 5],
[1, 4, 5],
[2, 4, 5],
[3, 4, 5],
[4, 4, 5],
[5, 4, 5],
[6, 4, 5],
[7, 4, 5],
[8, 4, 5],
[-999, 4, 6],
[8, 0, 0]
]


Output

[["diamond",56],["diamond",1],["diamond",1],["diamond",1],["diamond",1],["diamond",1],["diamond",1],["diamond",1],["diamond",1]]


# Meta

I have no clue what I'm doing writing a question.

Tagged code golf

Critique goals:

• Improve testcases
• Improve description of problem
• Determine if the problem is too complex
• Challenges are meant to be self-contained. While information where the idea/process comes from can be nice, everything needed to solve the challenge should be in the description. This means you should write down what click does what, for all the people who don't remember what Minecraft clicks do by heart. Nov 22 '19 at 6:43

A very-very old (maybe early 2000s) problem:

Print out a decimal number $$\n\$$ such as $$\n^2\$$ ends with $$\n\$$ with maximal length your program can compute in 60 seconds

In other words it's needed to find some long enough $$\n\$$ such as $$\10^{\lfloor\log_{10}n\rfloor+1}|(n^2-n)\$$.
A hint may be that an $$\n\$$ ending with $$\5\$$ is more easy to compute than an $$\n\$$ ending with $$\6\$$.

• How can this be king-of-the-hill? Do you mean code-challenge? And what stops us from hardcoding some extremely large number?
– Jo King Mod
Nov 21 '19 at 23:36
• king-of-the-hill needs interaction between submissions. I don't see any here
– Jo King Mod
Nov 22 '19 at 1:43
• @JoKing the problem becomes very simple with modular arithmetic: got 205k digits for free with ~len(n) time for each step imgur.com/ExPdwMb , so there's no need for hardcoding and it's not much interesting. ) Nov 22 '19 at 14:11

# JavaScript: Free for All

This is a very experimental idea of mine: given a function which is provided a single function as an argument, try to run that function the most times possible in a browser environment while competing against other bots.

## Bot submissions

Each bot consists of a function. This function takes a scoring function as input. Each bot has a state consisting of three values:

• score: Number indicating score, winning criterion
• locked: Boolean which, when true, prevents further score increases
• calls: Number of times scoring function called in last 100ms (?), will set locked to true for the remainder of the round if it exceeds a certain value

The scoring function increments score and calls, as long as locked is not true.

## Restrictions

If any of these restrictions are violated, a bot will have locked set to true.

No bot or bot-defined function may:

• Run longer than 5ms
• Attempt to modify the window location (location.href, location.assign, etc.)
• Attempt to connect to the internet (AJAX, WebSockets, etc.)
• Create web workers
• Affect hardware (sound, microphone, camera, USB, gamepads, etc.)
• Leave an impact which cannot be fixed by reloading the page

## Notes

This is almost certainly a very bad idea on an assortment of levels. If you have any suggestions of restrictions or ways to make the challenge more interesting, be sure to comment.

I'm considering some sort of system to determine which bot runs first that adds to the strategy, and interesting attack angles for other bots.

To prevent this from becoming a "read the last answer and exactly cancel out its strategy" type thing, I'm open to any suggestions.

Given a digit as an English word, output its numerical value.

For example, given the input one, you should output 1 (optionally with a trailing newline).

Your program should cover all the following cases:

zero  => 0
one   => 1
two   => 2
three => 3
four  => 4
five  => 5
six   => 6
seven => 7
eight => 8
nine  => 9


# Introduction

This challenge was inspired by the 24 Game.

In the 24 Game, you are given 4 numbers and are asked to make 24 using addition, subtraction, multiplication, division, and parentheses. So...

What is the biggest number you can make given 4 numbers using the above operations?

# Challenge

For four given inputs a, b, c, d, output the biggest number you can get using addition, subtraction, multiplication, division, and parentheses.

This is code-golf, so the shortest answer wins.

# Example Input and Output

  Input  -->  Output  -->   Explanation
1,3,2,4 -->    36    --> (1 + 2) × 3 × 4
5,5,5,5 -->   625    -->  5 × 5 × 5 × 5
9,2,3,1 -->    81    --> (1 + 2) × 3 × 9



Please give feedback on this challenge and correct me if my outputs are wrong. Should I change it to the smallest number?

• Dec 30 '19 at 23:19
• Also the subtraction and division are surely obsolete for the challenge? Dec 30 '19 at 23:21
• Will positive number divide zero yield Infinity as what IEEE 754 does?
– tsh
Dec 31 '19 at 3:37
• Shouldn't (1+2)x3x4 greater than 1+2x3x4?
– tsh
Dec 31 '19 at 3:37
• @FlipTack Probably but maybe not in some circumstances. Dec 31 '19 at 22:18
• @tsh No, infinity will not count as the solution. Thank you, that is true that (1+2)x3x4 is greater. Dec 31 '19 at 22:19
• Does order matter? From the input it seems the order matters, i.e. we are not supposed to change the order of the input. So, for 1,3,2,4, the answer is 32, rather than 36. Jan 1 '20 at 5:25
• @Element118 No, order does not matter, those were just the random numbers that came from my head. Jan 4 '20 at 21:11

# How many ACus do I have?

Posted to main

• I'm not sure this counts as a dupe, but what it seems to be is n=floor(days_between(input, date(1,1,2020)) / 7); return n*(n-1)/2, which doesn't seem terribly interesting to golf. (Also just fyi, the 01 you used in your dates in your script is actually an octal literal i.e. 010 is 8) Jan 7 '20 at 21:33
• Thanks for the feedback. I have corrected the script. Not sure how the extra 0's managed to slip in! I'll leave the challenge here for a couple more days to see if there are any more comments. Jan 8 '20 at 7:43
• @ElPedro You need to wait longer. At least a month or two, but a few months is really good. Jan 11 '20 at 21:25
• I'm sorry and no personal offence intended but I find it a bit strange that a member of 3 months is telling a member of over 4 years with lot's of experience and over 5000 rep how to use the sandbox and the main site. Maybe I am simply getting too old for this community. Jan 11 '20 at 21:36
• And besides which, none of that alters my opinion that downvotes without the downvoter giving a reason are not any help to anyone. If you think differently then please feel free to give me a good reason. I am happy to listen and learn. Jan 11 '20 at 21:40

# Make a Decompiler Bomb

Similar to the Make a Compiler Bomb challenge, but backwards.

The goal is to create the a 1KiB (1024 bytes) or smaller bytecode file that creates the largest output when decompiled.

# Constraints

• A binary is either an x86 binary (in the form of an ELF file, PE file (.dll/.exe), or Mach-O binary) or a virtual bytecode file (e.g. Python .pyc, Java .class, .NET CLR, etc.)

• The decompiler can be any public (preferably free) decompiler of your choice. (e.g Snowman/Hex-Rays for x86 binarys, CFR/Fernflower/etc. for java, dotPeek for .NET, uncompyle6 for Python, etc.)

• A decompiler is any tool that takes a binary and attempts to reconstruct human readable source code from it.

• The largest output byte count wins, with the smallest input size as a tie-breaker

• The binary must be executable, and print "Hello World!"

• The decompiled code must be syntactically correct

• I think you probably want to specify what a "decompiler" is, since really any file is "binary" and anything that takes that and produces some valid code probably arguable counts as a decompiler. Further, I think you might be better served by limiting the binary size, like the original challenge, as if someone finds a way that adding $n$ bytes adds more than $n^{2}$ bytes to the output they would achieve an arbitrarily large score. Jan 17 '20 at 20:06
• @FryAmTheEggman I put in a basic explanation and made the scoring based on largest output rather than a formula. Explaining a decompiler is tricky though, I'll think about that more and maybe edit for it later. Jan 21 '20 at 14:15
• I think the scoring change you made is good, only that kb is a tad ambiguous between being 1000 or 1024, and that it seems a tad large (but neither of those is critical and the second is just my opinion). Thinking about what to do with the problem of defining a decompiler, I realised it was probably a good idea to require that the resulting decompiled code does something. Maybe requiring that the decompiled code is a hello world variant or something will limit some problems like "this program converts to Unary source code". Jan 21 '20 at 16:27
• @FryAmTheEggman Made it so the decompiled code must have correct syntax, and made the size smaller, was going to post my java example but I just realized I have to make it fit in the new restrictions so... Jan 21 '20 at 16:46

# I delete the input, you delete the source code

This is a new twist on the long running series on CGCC.

Your task, if you accept it, is to write a program/function that outputs/returns the contents of an input file. The tricky part is that if I delete the input file, your program must delete itself.

## Rules

• The source code file and the input file should be in the same directory.

• The input file and source file can be named anything at all. I.e. The file names are your choice.

• The contents of the input file will be restricted to printable ASCII.

• The input file and the source file must be deletable.

• This is code-golf, so the shortest (original) code in each language wins!

• Default Loopholes apply.

## Example

If your program is jspwjxnlow8229 and the input file exists, the program must print the contents of the file. If the file doesn't exist, the program must delete itself.

## Feedback

In regards to file manipulation, have I specified the rules enough?

• What about languages in which programs don't live in files but rather in binary blobs? Is it enough for the program to delete itself from the binary blob?
Jan 22 '20 at 9:30
• Can the program and/or source file also be named anything at all?
Jan 22 '20 at 9:32
• @Adam, forgive me for not knowing, but what's a binary blob? Jan 22 '20 at 9:32
• It doesn't matter what a binary blob is. I just wanted you to be aware than not all languages use the same model.
Jan 22 '20 at 9:33
• @Adam sure. I'll add a part about that to the challenge Jan 22 '20 at 9:34
• Parts of this feel a bit unclear. Can the submissions know the file names in advance? (If not then the name feels a bit odd, isn't it really write a cat program that deletes itself if the input name doesn't correspond to an existing file? They aren't really tied together in that case) Similarly, why mention the recycling bin? It isn't present on many systems, and behaves differently on those that do have one (most programmatic deletions will require more work to send the file to the temporary "are you sure" location). Jan 22 '20 at 17:06

# How healthy are my children?

As anyone who has twins will know, it can be hard to keep track of which child fed / was changed, and when.

That's why I've devised a system using OneNote on my phone. It's quick and easy to use.

Each entry (line) uses the following structure (note: I'm not a regex expert and the expression is more permissive than I want - see words for detail):

(ddMMyyyy )?HHmm ((1|2|B) (💧|💩|🤱){1,3}){1,3}

Or, in words:

1. For the first entry on or after midnight each day only, each line starts with the date.
2. The next component is always the time, hour and minute in 24 hour clock format
3. Next is a child identifier character - 1 or 2; or B if what follows applies to both children. All subsequent emoticons apply to the identified child, until a new child identifier is found or a newline. There is guaranteed to be at least one child identifier in a record.
4. Next comes any or all of the three emoticons (maximum one of each) representing a wet nappy (💧), a dirty nappy (💩) or a feed (🤱)
5. Repeat from step 3. until done. BUT - each emoticon will only appear once per child - so if it appears in B then it won't appear in either 1 or 2; and if it appears in either 1 or 2 it won't appear in B. It won't appear in both 1 and 2 (because then it would be in B instead). The regex doesn't show this subtlety.

Some other notes:

• Breast-Feeding (feed) emoticon 🤱 is codepoint U+1F931
• Droplet (wet) emoticon 💧 is codepoint U+1F4A7
• Pile of Poo (dirty) emoticon 💩 is codepoint U+1F4A9
• All items in the string are space-separated
• I would actually use the initials of my children's names, rather than 1 and 2 - but for the challenge I went with the numbers instead.

## Example

02022020 0005 1 💩 B 💧 🤱
0230 2 💧 🤱
0250 1 💧 💩 🤱
0330 2 🤱
0400 1 🤱
0700 B 💧 🤱
0900 2 🤱
1000 2 💧 🤱
1020 1 💧 🤱
1220 1 🤱
1420 B 💧 1 💩 2 🤱
1440 1 🤱
1600 2 💧 💩
1700 1 💧
1745 B 🤱
2100 B 💧 🤱 1 💩
2350 2 🤱 B 💩 1 💧
03022020 0015 1 🤱 B 💧
0500 1 💧 🤱
0830 1 💧 🤱
0900 2 💧 🤱
1115 B 💧 1 💩
1215 B 🤱
1330 B 🤱
1400 2 💧 💩

# The Challenge

Given the raw data, input as a single string or array of entries, containing data such as the above example, output a summary of:

• number of feeds, wet and dirty nappies, per baby, over the past 24 hours

"The past 24 hours" can be either based on system time, or the current time can be passed as an extra input.

The output format is up to you, as long as it:

a) is consistent across all runs of the program
b) shows the information required

some example outputs for the above inputs, with a current time of 14:30 on 3rd of February 2020 (hand-calculated, sorry if they're not right!):

Baby 1 had 6 wet nappies, 2 dirty nappies, and fed 8 times Baby 2 had 6 wet nappies, 3 dirty nappies and fed 6 times

{{6,6},{2,3},{8,6}}

{6,2,8},{6,3,6}

etc.

This is so lowest bytes wins. Usual exclusions apply.

• If a language can't deal with unicode input, should I allow the whole codepoint string substituted in its place? Feb 14 '20 at 11:59
• Should I be more explicit with the output format? Feb 14 '20 at 12:00
• Can someone help me make the regex more tight? Feb 14 '20 at 12:05

I want to ask a combined popularity / objectively scored question. Something like:

Take a string as input. Match the string to a famous painting such as "Mona Lisa" and render a cartoon version of it. 1 point per painting, 1 point per upvote. Voting closes on XX/YY/ZZZZ.

I want to reward people for including more possibilities (there will be a fixed upper limit, unlike with paintings). I also want to reward people for the quality of their renderings. The cartoon paintings should be recognisable as versions of the real paintings.

Is this a good scoring system? If not, what would be better?

• This is somewhat vague. Can you be more precise? Feb 17 '20 at 15:38

# Implement PSL(2,3)

Since challenge to implement Galois field already have been many, I'm writing a challenge involving a group of Lie type!

## Objective

Implement the multiplication and inversion in $$\\text{PSL}(2,3)\$$.

## The ring $$\\mathbb{Z}_3\$$

The ring $$\\mathbb{Z}_3\$$ is the set $$\\{0,1,2\}\$$ with addition, negation, subtraction, and multiplication defined as modular arithmetic:

• Addition is the usual addition with the result moduloed by 3;

• Negation, subtraction, and multiplication are also analogously defined.

Reciprocal and division is also well-defined, but that's just another detail.

## The group $$\\text{SL}(2,3)\$$

The multiplicative group $$\\text{SL}(2,3)\$$ is the set of 2-by-2 matrices whose entries are members of $$\\mathbb{Z}_3\$$ and the determinant is $$\1\$$. Note that the determinant is calculated using modular arithmetic. Matrix multiplication and matrix inversion is defined as:

• Matrix multiplication is the usual matrix multiplication, where addition and multiplication of the entries are modular;

• Matrix inversion of $$\\begin{pmatrix} a & b \\ c & d \end{pmatrix}\$$ is $$\\begin{pmatrix} d & -b \\ -c & a \end{pmatrix}\$$. This exploits that the determinant is $$\1\$$.

As a consequence, the elements of $$\\text{SL}(2,3)\$$ are:

$$\begin{pmatrix} 0 & 1 \\ 2 & 0\end{pmatrix}, \begin{pmatrix} 0 & 1 \\ 2 & 1\end{pmatrix}, \begin{pmatrix} 0 & 1 \\ 2 & 2\end{pmatrix}, \begin{pmatrix} 0 & 2 \\ 1 & 0\end{pmatrix}, \begin{pmatrix} 0 & 2 \\ 1 & 1\end{pmatrix}, \begin{pmatrix} 0 & 2 \\ 1 & 2\end{pmatrix}, \begin{pmatrix} 1 & 0 \\ 0 & 1\end{pmatrix}, \begin{pmatrix} 1 & 0 \\ 1 & 1\end{pmatrix}, \begin{pmatrix} 1 & 0 \\ 2 & 1\end{pmatrix}, \begin{pmatrix} 1 & 1 \\ 0 & 1\end{pmatrix}, \begin{pmatrix} 1 & 1 \\ 1 & 2\end{pmatrix}, \begin{pmatrix} 1 & 1 \\ 2 & 0\end{pmatrix}, \begin{pmatrix} 1 & 2 \\ 0 & 1\end{pmatrix}, \begin{pmatrix} 1 & 2 \\ 1 & 0\end{pmatrix}, \begin{pmatrix} 1 & 2 \\ 2 & 2\end{pmatrix}, \begin{pmatrix} 2 & 0 \\ 0 & 2\end{pmatrix}, \begin{pmatrix} 2 & 0 \\ 1 & 2\end{pmatrix}, \begin{pmatrix} 2 & 0 \\ 2 & 2\end{pmatrix}, \begin{pmatrix} 2 & 1 \\ 0 & 2\end{pmatrix}, \begin{pmatrix} 2 & 1 \\ 1 & 1\end{pmatrix}, \begin{pmatrix} 2 & 1 \\ 2 & 0\end{pmatrix}, \begin{pmatrix} 2 & 2 \\ 0 & 2\end{pmatrix}, \begin{pmatrix} 2 & 2 \\ 1 & 0\end{pmatrix}, \begin{pmatrix} 2 & 2 \\ 2 & 1\end{pmatrix}$$

## The factor group $$\\text{PSL}(2,3)\$$

$$\\text{PSL}(2,3)\$$ is defined as cosets of $$\\text{SL}(2,3)\$$ by $$\\{\begin{pmatrix} 1 & 0 \\ 0 & 1\end{pmatrix}, \begin{pmatrix} 2 & 0 \\ 0 & 2\end{pmatrix}\}\$$. That is, elementwise multiplications of $$\\{\begin{pmatrix} 1 & 0 \\ 0 & 1\end{pmatrix}, \begin{pmatrix} 2 & 0 \\ 0 & 2\end{pmatrix}\}\$$. They are: $$\{\begin{pmatrix} 0 & 1 \\ 2 & 0\end{pmatrix}, \begin{pmatrix} 0 & 2 \\ 1 & 0\end{pmatrix}\}, \{\begin{pmatrix} 0 & 1 \\ 2 & 1\end{pmatrix}, \begin{pmatrix} 0 & 2 \\ 1 & 2\end{pmatrix}\}, \{\begin{pmatrix} 0 & 1 \\ 2 & 2\end{pmatrix}, \begin{pmatrix} 0 & 2 \\ 1 & 1\end{pmatrix}\}, \{\begin{pmatrix} 1 & 0 \\ 0 & 1\end{pmatrix}, \begin{pmatrix} 2 & 0 \\ 0 & 2\end{pmatrix}\}, \{\begin{pmatrix} 1 & 0 \\ 1 & 1\end{pmatrix}, \begin{pmatrix} 2 & 0 \\ 2 & 2\end{pmatrix}\}, \{\begin{pmatrix} 1 & 0 \\ 2 & 1\end{pmatrix}, \begin{pmatrix} 2 & 0 \\ 1 & 2\end{pmatrix}\}, \{\begin{pmatrix} 1 & 1 \\ 0 & 1\end{pmatrix}, \begin{pmatrix} 2 & 2 \\ 0 & 2\end{pmatrix}\}, \{\begin{pmatrix} 1 & 1 \\ 1 & 2\end{pmatrix}, \begin{pmatrix} 2 & 2 \\ 2 & 1\end{pmatrix}\}, \{\begin{pmatrix} 1 & 1 \\ 2 & 0\end{pmatrix}, \begin{pmatrix} 2 & 2 \\ 1 & 0\end{pmatrix}\}, \{\begin{pmatrix} 1 & 2 \\ 0 & 1\end{pmatrix}, \begin{pmatrix} 2 & 1 \\ 0 & 2\end{pmatrix}\}, \{\begin{pmatrix} 1 & 2 \\ 1 & 0\end{pmatrix}, \begin{pmatrix} 2 & 1 \\ 2 & 0\end{pmatrix}\}, \{\begin{pmatrix} 1 & 2 \\ 2 & 2\end{pmatrix}, \begin{pmatrix} 2 & 1 \\ 1 & 1\end{pmatrix}\},$$

You pick an element of each coset as representives, and don't care about the rest.

Multiplication/inversion of such representives is defined as multiplication/inversion in $$\\text{SL}(2,3)\$$, then taking the representive of the coset the multiplication/inversion is in. For example, $$\\begin{pmatrix} 0 & 1 \\ 2 & 0\end{pmatrix}^2 = \begin{pmatrix} 1 & 0 \\ 0 & 1\end{pmatrix}\$$, if $$\\begin{pmatrix} 0 & 1 \\ 2 & 0\end{pmatrix}\$$ and $$\\begin{pmatrix} 1 & 0 \\ 0 & 1\end{pmatrix}\$$ are representives.

## Examples

Picking the left elements as representives of the cosets above: $$\begin{pmatrix} 0 & 1 \\ 2 & 0\end{pmatrix}^2 = \begin{pmatrix} 1 & 0 \\ 0 & 1\end{pmatrix}, \begin{pmatrix} 0 & 1 \\ 2 & 1\end{pmatrix}^2 = \begin{pmatrix} 1 & 2 \\ 1 & 0\end{pmatrix}, \begin{pmatrix} 1 & 0 \\ 0 & 1\end{pmatrix}\begin{pmatrix} 1 & 1 \\ 1 & 2\end{pmatrix} = \begin{pmatrix} 1 & 1 \\ 1 & 2\end{pmatrix}, \begin{pmatrix} 1 & 2 \\ 2 & 2\end{pmatrix}\begin{pmatrix} 1 & 1 \\ 1 & 2\end{pmatrix} = \begin{pmatrix} 0 & 1 \\ 2 & 0\end{pmatrix}, \begin{pmatrix} 1 & 2 \\ 2 & 2\end{pmatrix}^{-1} = \begin{pmatrix} 1 & 2 \\ 2 & 2\end{pmatrix}$$ To be more specific about the method of evaluation: $$\begin{pmatrix} 0 & 1 \\ 2 & 1\end{pmatrix}\begin{pmatrix} 0 & 1 \\ 2 & 2\end{pmatrix} ≡ \begin{pmatrix} 2 & 2 \\ 2 & 4\end{pmatrix} ≡ \begin{pmatrix} 2 & 2 \\ 2 & 1\end{pmatrix} ≡ \begin{pmatrix} 1 & 1 \\ 1 & 2\end{pmatrix}, \\ \begin{pmatrix} 1 & 1 \\ 1 & 2\end{pmatrix}^{-1} ≡ \begin{pmatrix} 2 & -1 \\ -1 & 1\end{pmatrix} ≡ \begin{pmatrix} 2 & 2 \\ 2 & 1\end{pmatrix} ≡ \begin{pmatrix} 1 & 1 \\ 1 & 2\end{pmatrix}$$ The steps of this algorithm is:

1. Do usual matrix multiplication/inversion;
2. Modulo the entries by 3;
3. Take the representive of the coset.

Though you can make any possible algorithm.

## Rules

• Input type and format doesn't matter, but it must be a container of integers. In C, int[2][2] and int[4] are valid examples. This restriction prevents abusing the fact that $$\\text{PSL}(2,3) \cong A_4\$$.
• Output type and format doesn't matter either, but it must be the same as the input type and format.
• Invalid inputs fall in don't care situation.
• Multiplication and inversion may be in separate codes. In this case, the score is the sum of their lengths in bytes.
• Since this is a code-golf, the code with least score wins.
• This challenge appears to heavily rely on restricted-source and thus to me does not seem too viable. Feb 25 '20 at 0:58
• @JonathanFrech Do you think I should lift the restriction on input type? Otherwise, "You pick an element of each coset as representives, and don't care about the rest" and "Invalid inputs fall in don't care situation" should be enough. Feb 25 '20 at 3:38

## Very rough outline of a challenge that rewards short programs that take a long time.

Probably a no input and output can be anything except an error challenge.

Is there a nice way to exclude things like sleep(), wait() etc?

Would be required for 1 person to run all the programs for the timing to be fair.

Thinking that answers would include loops, recursion, testing of complex criteria.

• I think you would have to post your challenge as a popularity contest ... a slippery slope indeed. Mar 15 '20 at 23:43

# The (All But) Quine challenge

Like a quine challenge, but the opposite. Print everything except source code

# Challenge

Write a program, which takes no input, and outputs all the strings of printable characters which are the same length as the source code of the program, except the source code of the program.

# Scoring

The shortest program (per language) to accomplish the above task, wins

• By 'printable characters' you mean printable ASCII characters (code-points [32,126])? What if I use a language that don't contain any ASCII characters in its source code? Mar 20 '20 at 13:38
• If your program is in ASCII, then you would need to print all of the ASCII characters, if the program is in Unicode, then you would have to print all of the Unicode characters Mar 20 '20 at 14:40
• @Benji Would you consider a Python 3 source file as being "in Unicode"? Mar 22 '20 at 17:49
• If there are any Unicode characters that are used in the file, then no. If Unicode characters are used, then I would consider it to be Unicode Mar 23 '20 at 14:47

## Numbers by index

Challenge

Print the numbers:

0
1
22
333
4444
55555
666666
7777777
88888888
999999999


In that order.

I/O

Takes no input. The numbers can have any delimiters desired (or none). Example outputs:

0122333444455555666666777777788888888999999999

[0,1,22,333,4444,55555,666666,7777777,88888888,999999999]

etc....


Code Example

This is an un-golfed example that may perhaps act as algorithm guide (or maybe not):

# Turing Machine Code, 553 bytes

0 * 0 r K
K * _ r 1
1 * 1 r L
L * _ r 2
2 * 2 r a
a * 2 r M
M * _ r 3
3 * 3 r b
b * 3 r c
c * 3 r N
N * _ r 4
4 * 4 r d
d * 4 r e
e * 4 r f
f * 4 r O
O * _ r 5
5 * 5 r g
g * 5 r h
h * 5 r i
i * 5 r j
j * 5 r P
P * _ r 6
6 * 6 r k
k * 6 r l
l * 6 r m
m * 6 r n
n * 6 r o
o * 6 r Q
Q * _ r 7
7 * 7 r p
p * 7 r q
q * 7 r r
r * 7 r s
s * 7 r t
t * 7 r u
u * 7 r R
R * _ r 8
8 * 8 r v
v * 8 r w
w * 8 r x
x * 8 r y
y * 8 r z
z * 8 r A
A * 8 r B
B * 8 r S
S * _ r 9
9 * 9 r C
C * 9 r D
D * 9 r E
E * 9 r F
F * 9 r G
G * 9 r H
H * 9 r I
I * 9 r J
J * 9 r halt


Try it online!

This prints out the numbers with a space delimiter:

0 1 22 333 4444 55555 666666 7777777 88888888 999999999


Challenge Type

, so shortest answer in bytes (by language) wins.

Edit: Link to the related challenge. Curiously, there is one answer on there where if it was by index, and the zero was included, it would be shorter.

• Nice challenge! Are preceding & trailing whitespace (during string output) permitted?
– user92069
Mar 11 '20 at 3:22
• I think it should also be kolgomorov-complexity. Mar 11 '20 at 5:19
• I don't like how the zero breaks the pattern of having the digit N appear N times -- it seems like an exceptional edge case. I think it would be better for 0 not to appear, so the numbers would just start from 1.
– xnor
Mar 11 '20 at 7:06
• @xnor, I knew you wouldn't like it (and probably a few other won't as well) That's on purpose. It just seems a little too easy otherwise. Mar 11 '20 at 7:28
• @a'_', Yes. @ PkmnQ, Noted. Mar 11 '20 at 7:29
• I don't really see how adding a fixed zero to the beginning makes the challenge harder in almost any language. In some, the empty string will actually convert to zero, which makes it more natural but still fairly trivial. I feel like you probably either want to go with omitting the zero, or finding a different way to make the challenge more complicated. Mar 11 '20 at 14:53
• @FryAmTheEggman, How can you have a challenge about indexes and not have zero? That just seems wrong. Mar 11 '20 at 15:31
• Most people start counting from one - only people who use computers a lot default to starting at zero. And separately, I think finding another way to incorporate it is better than leaving it out (I just also think both are better than having an unexplained outlier). Mar 11 '20 at 15:40
• @FryAmTheEggman, But it's not really unexplained is it? It's the index of the first number. Mar 11 '20 at 15:46
• As per what xnor said, it doesn't match the pattern of the others. That behaviour is not explained. Comments aren't really for a discussion like this; if you disagree that is fine. I've just given feedback on how I think you could improve the challenge. Mar 11 '20 at 16:15
• I do want to make sure that everyone knows that I am VERY grateful for the feedback! I also appreciate having a Sandbox where we can have this discussion here instead of on the main site. Mar 11 '20 at 16:18
• @FryAmTheEggman, It's not that I disagree. I kind of agree. I like that leading zero in there to represent the index location of the initial value. I considered this when I thought of the question, before posting it here. It breaks up a trivial loop sequence answer a bit, or maybe even inspires a clever solution that nobody considered. I'd like to keep it because it stands out like that, not despite that. Mar 11 '20 at 16:21
• I posted an example implementation above. The zero wasn't a big deal. Mar 11 '20 at 16:31
• My guess is that you're excited about the arithmetic expression 10**n/9*n or similar. But I don't think that's much more interesting than the obvious loops that removing the zero would allow unmodified.
– xnor
Mar 11 '20 at 21:59
• @ouflak I contrast, I am very excited about arithmetic expressions :)
– xnor
Mar 12 '20 at 21:16

# A malbolge interpreter

The challenge today is to write a Malbolge interpreter.

## Specification

Malbolge

I hereby relenquish any and all copyright on this language,
documentation, and interpreter; Malbolge is officially public domain.

------------------------------------------------------------------------

Malbolge

Introduction
^^^^^^^^^^^^

It was noticed that, in the field of esoteric programming languages,
there was a particular and surprising void: no programming language
known to the author was specifically designed to be difficult to program
in.

Certainly, there were languages which were difficult to write in, and
far more were difficult to read (see: Befunge, False, TWDL, RUBE...).
But even INTERCAL and BrainF***, the two kings of mental torment, were
designed with other goals: INTERCAL to have nothing in common with any
major programming language, and BrainF*** to be a very tiny, yet still
Turing-complete, language.

INTERCAL's constructs are certainly tortuous, but they are all too
flexible; you can, for instance, quite easily assign any number to a
variable with a single statement.

BrainF*** is lacking the flexibility which is INTERCAL's major weakness,
but it fails in that its constructs are far, far too intuitive.
Certainly, there are only 8 instructions, none of which take any
arguments--but it is quite easy to determine how to use those
instructions.  Subtract 8 from the current number?  With a simple
'--------' you are done!  This kind of simple answer was unacceptable to
the author.

Hence the author created Malbolge.  It borrows from machine, BrainF***,
and tri-INTERCAL, but put together in a unique way.  It was designed to
be difficult to use, and so it is.  It is designed to be
incomprehensible, and so it is.

So far, no Malbolge programs have been written.  Thus, we cannot give an
example.

"Malbolge" is the name of Dante's Eighth Circle of Hell, in which
practitioners of deception (seducers, flatterers, simonists, thieves,
hypocrites, and so on) spend eternity.

Environment
^^^^^^^^^^^

In many languages, the environment is easy to understand.  In Malbolge,
it is best to understand the runtime environment before you ever see a
command.

The environment is, roughly, that of a primitive trinary CPU.  Both code
and data share the same space (the machine's memory segment), and there
are three registers.  Machine words are ten trits (trinary digits) wide,
giving a maximum possible value of 59048 (all numbers are unsigned).
Memory space is exactly 59049 words long.

The three registers are A, C, and D.  A is the accumulator, used for
data manipulation.  A is implicitly set to the value written by all
write operations on memory.  (Standard I/O, a distinctly non-chip-level
feature, is done directly with the A register.)

C is the code pointer.  It is automatically incremented after each
instruction, and points the instruction being executed.

D is the data pointer.  It, too, is automatically incremented after each
instruction, but the location it points to is used for the data
manipulation commands.

All registers begin with the value 0.

When the interpreter loads the program, it ignores all whitespace.  If
it encounters anything that is not one of an instruction and is not
whitespace, it will give an error, otherwise it loads the file, one non-
whitespace character per cell, into memory.  Cells which are not
initialized are set by performing op on the previous two cells
repetitively.

Commands
^^^^^^^^

When the interpreter tries to execute a program, it first checks to
see if the current instruction is a graphical ASCII character (33
through 126).  If it is, it subtracts 33 from it, adds C to it, mods it
by 94, then uses the result as an index into the following table of 94
characters:

+b(29e*j1VMEKLyC})8&m#~W>qxdRp0wkrUo[D7,XTcA"lI
.v%{gJh4G\-=O@5_3i<?Z';FNQuY]szf$!BS/|t:Pn6^Ha It then checks it against the characters listed below, and performs an appropriate action. If the result is not one of the characters listed below, it is treated as a nop. If the original character is not graphic ASCII, the program is immediately ended. When the interpreter parses the input file, it checks each non- whitespace character with the process above. If any result is not one of the eight characters below, the file will be rejected. After the instruction is executed, 33 is subtracted from the instruction at C, and the result is used as an index in the table below. The new character is then placed at C, and then C is incremented. 5z]&gqtyfr$(we4{WP)H-Zn,[%\3dL+Q;>U!pJS72FhOA1C
B6v^=I_0/8|jsb9m<.TVacuY*MK'X~xDl}REokN:#?G"i@

j
sets the data pointer to the value in the cell pointed to by the
current data pointer.

i
sets the code pointer to the value in the cell pointed to be the
current data pointer.

*
rotates the trinary value of the cell pointed to by D to the right 1.
The least significant trit becomes the most significant trit, and all
others move one position to the left.

p
performs a tritwise "op" on the value pointed to by D with the
contents of A.  The op (don't look for pattern, it's not there) is:

| A trit:
________|_0__1__2_
0 | 1  0  0
*D  1 | 1  0  2
trit 2 | 2  2  1

Di-trits:
00 01 02 10 11 12 20 21 22

00  04 03 03 01 00 00 01 00 00
01  04 03 05 01 00 02 01 00 02
02  05 05 04 02 02 01 02 02 01
10  04 03 03 01 00 00 07 06 06
11  04 03 05 01 00 02 07 06 08
12  05 05 04 02 02 01 08 08 07
20  07 06 06 07 06 06 04 03 03
21  07 06 08 07 06 08 04 03 05
22  08 08 07 08 08 07 05 05 04

<
reads an ASCII value from the stdin and converts it to Trinary, then
stores it in A.  10 (line feed) is considered 'newline', and
2222222222t (59048 dec.) is EOF.

/
converts the value in A to ASCII and writes it to stdout.  Writing
10 is a newline.

v
indicates a full stop for the machine.

o
does nothing, except increment C and D, as all other instructions do.

Turing-Completeness
^^^^^^^^^^^^^^^^^^^

Though I have not proven it, I _think_ Malbolge to be Turing-complete.
To be Turing-complete, there must be some data construct which can be
used to do any mathematical calculation.  I believe that using *p in
various clever ways on the tritwords can fulfill this requirement.

Turing-completeness also requires three code constructs: sequential
execution (which Malbolge obviously has), repetition (provided by the
i and, indirectly, j instructions), and conditional-execution (provided,
I believe, by self-modifying code and altering i destinations).

I do have my doubts, particularly about data constructs, but I *think*
this works...

Appendix: Trinary Conversion Table
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Trinary to ASCII to decimal to hex table, provided, strangely enough,
for the convenience of Malbolge programmers.

00000 NUL 000 00    01012   032 20    02101 @ 064 40    10120  096 60
00001 SOH 001 01    01020 ! 033 21    02102 A 065 41    10121 a 097 61
00002 STX 002 02    01021 " 034 22    02110 B 066 42    10122 b 098 62
00010 ETX 003 03    01022 # 035 23    02111 C 067 43    10200 c 099 63

# Find the nth positive integer m for which $$\\tan(m) > m\$$code-golfmath

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

## Scoring

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?

• +1 for referencing a MegaFavNumbers video. Aug 20 '20 at 3:24
• 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? Aug 20 '20 at 3:33
• Where is n in the equation? I'm lost. Aug 20 '20 at 9:07
• @Razetime On the channel Stand-up Maths, right? Aug 20 '20 at 18:49
• replace "nth" with "first" "second" etc -> "first/second/etc number m for which ..." i.e. n is not in the equation @V.Courtois Aug 20 '20 at 20:30
• @Mukundan314 maybe indicate that n is the input? Aug 20 '20 at 20:31
• @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. Aug 21 '20 at 6:50
• 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.
– xnor
Aug 22 '20 at 7:04
• 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. Aug 22 '20 at 22:14

# Is it a Pythagorean triple? code-golfdecision-problemgeometrymathnumber-theory

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.

## Rules

• 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


## Meta

• 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?
• possible duplicate of this challenge Oct 18 '20 at 13:38
• @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 Oct 18 '20 at 14:32
• 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. Oct 18 '20 at 15:04
• 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.
– xnor
Oct 19 '20 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?
• My personal feeling is that this is too easy. There's not really much scope for golfing the answer once you find the pattern. Oct 28 '20 at 0:25
• 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. Oct 28 '20 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'))

• 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. Jan 19 at 6:37
• @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. Jan 19 at 7:08
• @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. Jan 19 at 7:09
• 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. Jan 19 at 7:36
• @Bubbler Is banning eval not an objective restricted-source criterion, as opposed to “no built-ins”? Jan 19 at 19:28
• 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. Jan 21 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.


NOTE DON'T FORGET, THE PAINT MUST ALL BE DRY BEFORE YOU CAN RECEIVE YOUR PAYMENT!

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


Contraints

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


Dataset:

input: 1 1 12 0

output: 60

input: 5 2 5 30

output: 280

input: 1 5 5 200

output: 1045

• 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. Jan 28 at 0:16
• @Bubbler I have taken your remarks into consideration. I hope it's what you expected. Jan 28 at 9:31
• 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.' Jan 28 at 12:15
• 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.
– xnor
Jan 28 at 17:05
• @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 Jan 29 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!


To:

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.

# Scoring:

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

• 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) Feb 6 at 13:46
• @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!" Feb 6 at 13:55
• Besides being poorly-defined, it is also an non-observable behavior. Feb 6 at 14:02
• No, (hey, that's a link. Read it.) Feb 6 at 14:09
• Wait, that's not what I mean. I'll explain it later. Feb 6 at 14:47
• @user202729 Right... Feb 6 at 14:53
• 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" Feb 6 at 17:11
• @Davide I think that rule already existed in the "A point it reaches 'Hello World!'" but I'll add that anyway. Feb 6 at 19:26
• 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) Feb 7 at 6:37
• @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. Feb 7 at 15:22
• Okay, about the unobservable behavior, what I mean is... Feb 7 at 15:59
• 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] Feb 7 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.

• ... while we do have [fastest-code] on this site, there are specific requirements; restricting allowed programming languages is another problematic thing; Feb 8 at 14:38
• besides, this definitely sounds like that you're outsourcing your homework to this site. Feb 8 at 14:38
• @user202729 I already have a numpy solution... this is definitely not homework XD Feb 8 at 15:34
• @user202729 Okay, removed language restriction. Feb 8 at 15:35
• 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. Feb 9 at 2:07
• 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] Feb 9 at 2:11
• @user202729 Okey. Feb 9 at 2:27