# Sandbox for Proposed Challenges

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

Sandbox FAQ

## Posting

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

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

## Discussion

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

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

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

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

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

## Other

Search the sandbox / Browse your pending proposals

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!

## ROT47(code) code-golfciphersource-layout

ROT13 is a Caesar cipher where every letter is replaced by the 13th letter that follows it in the alphabet.

Every letter and its counterpart:

a b c d e f g h i j k l m n o p q r s t u v w x y z
n o p q r s t u v w x y z a b c d e f g h i j k l m

ROT47 is a deritave of ROT13 which includes all the ASCII printable characters except space. Rot47 substitutes every character with the 47th character that follows it in the ASCII range.

Every character and its counterpart:

! " # $% & ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < = > ? @ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z [ \ ] ^ _  a b c d e f g h i j k l m n o p q r s t u v w x y z { | } ~ P Q R S T U V W X Y Z [ \ ] ^ _  a b c d e f g h i j k l m n o p q r s t u v w x y z { | } ~ ! " #$ % & ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < = > ? @ A B C D E F G H I J K L M N O

I ROT47( your code) and you ROT47( the output)

• Your code is supposed to at least output 1 character within the [33,126] ASCII range.
• When ROT47 is applied on your code, the output should also be ROT47 of the previous output
• solve in the fewest bytes possible

Below a ROT47 converter taken from decode

var input = document.getElementById("input");
var editor = CodeMirror(input, {
lineNumbers: true,
tabSize: 2,
mode: 'javascript',
theme: 'monokai'
});
editor.setSize(900, 100);
document.getElementById("button").onclick = function(){
editor.setValue(rot47(editor.getValue()));
}

//implementation below from https://www.dcode.fr/rot-47-cipher
// Javascript
function rot47(x){
var s='';
for(var i=0;i<x.length;i++){
var j=x.charCodeAt(i);
if((j>=33)&&(j<=126)){
s+=String.fromCharCode(33+((j+14)%94));
}
else {
s+=String.fromCharCode(j);
}
}
return s;
}
<head>
<meta content="text/html;charset=utf-8" http-equiv="Content-Type">
<meta content="utf-8" http-equiv="encoding">
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.60.0/codemirror.min.js" integrity="sha512-hc0zo04EIwTzKLvp2eycDTeIUuvoGYYmFIjYx7DmfgQeZPC5N27sPG2wEQPq8d8fCTwuguLrI1ffatqxyTbHJw==" crossorigin="anonymous"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.60.0/theme/monokai.min.css" integrity="sha512-R6PH4vSzF2Yxjdvb2p2FA06yWul+U0PDDav4b/od/oXf9Iw37zl10plvwOXelrjV2Ai7Eo3vyHeyFUjhXdBCVQ==" crossorigin="anonymous" />
<body style="background-color:#333333
">
<div id="input">
</div></br>
<button id="button" style="background-color: #17202a
;color:white">ROT47</button>
</body>

### Meta questions:

• Is it an interesting challenge?
• Is the explanation clear?
• suggestion for a title.
• why does it look normal in edit mode but not in the result 😡. – Alex bries Mar 23 at 19:43
• Fixed the formatting. SE doesn't show tables unless they have an empty line before and after them – caird coinheringaahing Mar 23 at 19:56
• so valid answers and their input must be printable ASCII? Or should it ignore anything not printable? – Wzl Mar 24 at 16:45
• It looks like the reference implementation leaves non-printable characters and space alone. It would be helpful to specify that. – Wzl Mar 24 at 16:50
• Well, if you look on main, this is a alternate of an alternate of a rip-off of a rip-off of a rip-off of a rip-off of a rip-off of a rip-off. (see this). Which is not to say it's a bad challenge. – A username Mar 25 at 8:40

# To count the sum of all Unicode characters of a given input under an interesting constraint

• Welcome to the site, and thank you for using the sandbox! Can you confirm that answering with a normal (base-10) number is OK? – Adám Mar 25 at 6:37
• Thanks for the comment, edited accordingly- Final answer can to be calculated in any base (either Hexadecimal, or base-10 or binary as per the program) no need to convert back. – Aatmaj Mar 25 at 9:55
• I know you've posted this already, but generally I recommend leaving challenges in the sandbox for a week. – Adám Mar 25 at 11:19
• Ohk. I will remember it from the next time. thanks a lot – Aatmaj Mar 25 at 11:19
• I've edited this down to a stub now that it's been posted to save space – caird coinheringaahing Mar 30 at 21:38

# Sum of two squares

Given an integer $$\n\$$, determine whether $$\n\$$ can be expressed as the sum of two square numbers, that is $$\\exists a,b\in\mathbb Z|n=a^2+b^2\$$.

   0 -> truthy
1 -> truthy
2 -> truthy
3 -> falsy
4 -> truthy
5 -> truthy
6 -> falsy
7 -> falsy
11 -> falsy
9997 -> truthy
9999 -> falsy


Relevant OEIS sequences:

This is , so shortest answer as measured in bytes wins.

• This is a subset of this problem. – hyper-neutrino Mar 31 at 5:29
• @HyperNeutrino yes, and I have that listed as a related problem. There's actually another method of solving this problem involving prime factors which doesn't work for that one, so I'm hoping that's novel enough to warrant a separate challenge. – hakr14 Mar 31 at 18:16
• My bad, didn't notice the link. And yes, I don't think it'd be a duplicate here; I do agree that there will probably be unique approaches to this specific problem. – hyper-neutrino Mar 31 at 18:18
• A couple answers here used the prime-factorization approach, and a few used the approach of counting divisors of the form 4k+1 and 4k+3 respectively. – xnor Apr 2 at 6:50

# Irreducible Rube Goldberg Sort (WIP)

You are given a list containing at least 10 integers. You must sort them in the most complicated and roundabout way possible.

Your task is to write $$\n\$$ programs (or functions) which, when combined in a specific constant sequence (specifically, feeding the output of the current step into the input of the next step), result in a sorted version of the original list. This sequence of programs should be set up in such a way that the system will not work if any subset of steps is removed. (for example, compressing and decompressing the stream, roundabout encryption that cancels itself out, etc...)

Your score is $$\n\$$. Highest score wins.

## Rules, Clarifications, and Notes

• Standard rules and loopholes apply
• Any method of I/O is fair game. It does not need to be consistent across all programs/functions.
• You may use any number of programming languages to solve the problem.
• It should not take an unreasonably long time to sort a list of up to 1000 elements using your system of programs. It should be reasonable to run it from start to finish during a lunch break (30 minutes)
• Lists can contain any integer from -999,999,999 to 999,999,999, inclusive, and may contain indistinguishable duplicates.
• Your system of programs should work for lists of any size if given enough time and space.
• What is there to put an upper bound on the size, other than irreducibility? I'm almost certain there's a way to get an infinite score pretty trivially. – Redwolf Programs Apr 1 at 16:30
• I suspect there's a way to have an arbitrarily complicated sequence of programs as well and I'm not quite sure how to limit that, aside from performance (the 30 minute rule) – Beefster Apr 1 at 16:33
• Does the process have to be deterministic (e.g. no implementation of bogosort)? I think your rules imply that, but it might be good to state explicitly. – water_ghosts Apr 1 at 18:17
• Throwing in a randomizer step probably wouldn't be irreducible. – Beefster Apr 1 at 19:13
• So a recursive approach (e.g. one similar to Stooge sort) is a no-starter? – Bubbler Apr 4 at 23:31
• @Bubbler feeding a step's output into its own input is not allowed, so yes, that probably wouldn't work. Basically, the idea is that you could run this as a bash pipeline and no matter what the input sequence is, you wouldn't be able to remove any subset of steps and have it still work. – Beefster Apr 5 at 23:06

# Ball game KoTH

• For the controller, instead of telling the bot which one it is, you could just use positive numbers for being closer to the bot and negative numbers if it's on the other side. This might also potentially be interesting if the other player's energy and moves were unknown. – Redwolf Programs Mar 26 at 5:50
• You're the KoTH expert - I'll change those. – A username Mar 26 at 7:50

# Dominate a zero-sum game

Write a rectangular code that takes a rectangular input and output it. If the code is repeated horizonally and vertically for times, output the input rectangular repeated for same amount of times.

Take an example, if your submission is

CODE
HERE


, then program

CODECODECODECODE
HEREHEREHEREHERE
CODECODECODECODE
HEREHEREHEREHERE


inputting

01
23
45


should output

01010101
23232323
45454545
01010101
23232323
45454545

• Nice one. But I didn't understand if there is s specific output. – math Apr 4 at 11:51

Create a C program that is less than 120 characters the produces the most ASM possible.

This limit does not include the def of main, or including headers. If a function is called the chars in the function count toward limit. The same goes for macros. The compiler used will be GCC 10.2 -O3 targeting x86-64.

The code conforms to these parameters and produces the most instructions wins.

I have a few questions regarding this. Is the character limit too limiting? Is the choice of compiler a good one? Is the optimization level being -O3 a good idea? Please share any other thoughts you have.

Thanks

• I don’t see a reason to limit the size of the program. You could score based on Assembly Instructions per Source Byte to encourage small code sizes without excluding a clever 121 byte solution. I also don’t think the rules around #include headers and counting the size of any functions called are clear (How many characters are in printf?). You could ban explicit #includes but allow implicit function declarations as long as the compiler accepts them. – water_ghosts Apr 5 at 2:17
• Should printf be 6 chars or should it be the size of the definition of the function printf? I'm not sure about this. – expr_champ2 Apr 5 at 3:57

# KotH: Assembly Anarchy

Draft. Just posting this so I don't forget I had this idea. Feel free to suggest improvements to the general idea here.

Basically, there would be a computer with memory and a processor. Programs would be submitted in a custom assembly language, and they would try to run a function (their flag) as many times as possible. They could try to interfere with other programs, by doing things like replacing the pointer to another bot's flag with their own, or preventing other bots from being run.

• I like the concept. It needs a lot of fleshing out, though. – jumbot Apr 9 at 13:42

# Poor Man's DRM

Write a program that only prints Welcome at the first execution and first execution only. All executions after the first execution should only print Where money.

Anything is allowed as long as the following condition is met: An execution ends after the program exits. So the second execution can only start after the first execution exits completely.

Reason for the condition: to prevent submissions that linger around in the memory and keep a runtime counter.

• any things that are disallowed? E.g. can a program write to its source file? – Wzl Apr 8 at 20:18
• @Wezl no, actually that's what I originally had in mind when writing this, but I decided to keep all the options open. -- edit for clarification: by "no", I meant it is allowed. – goodguy Apr 8 at 20:18
• @goodguy Nice challenge. You may want to look at Standard Loopholes and main article – math Apr 9 at 14:36

# Cooperative counting

• looks like a nice challenge – math Apr 9 at 11:11
• I can't wait to code a bot for this challenge! – math Apr 10 at 8:56
• @math patience :) – jumbot Apr 10 at 9:45

# Find the traitor cops-and-robbers (WIP)

In this challenge, the cops are the robbers/moles and the robbers are the cops/investigators.

## Cops

Cops will write a program that will output one of the following strings:

• "Hello World!"
• "Totally not evil stuff"
• "Good morning"
• "Innocent things"

However, when n specific characters are removed, where 0 < n < length of cop's program, the resulting program should output one of the following strings:

• "Bye World!"
• "Top secret stuff"
• "Evil things"
• "Horrible morning"

Cops will reveal the original program and n, but not the resulting program. They will also reveal the 2 strings that must be outputted by the original and transformed programs.

A cop's score is $$\\binom n r\$$, or $$\\frac{n!}{r!(n-r)!}\$$, where $$\r\$$ is the size of the cop's program and $$\n\$$ is the number of characters to be deleted. The lower the score, the better.

### Rules

• The original and transformed program may output in different ways, as long as the cop specifies what they are.
• The characters to be deleted do not have to be adjacent.

## Robbers

Robbers must find a way to make the cop's program output the chosen 2nd string by removing any n characters (not necessarily the same as the cop's).

## Example cop

Python, n = 1

a = ["Totally not evil stuff", "Hello World!"][01]
print(a)


The original string is "Hello World!", and the transformed program prints "Totally not evil stuff".

## Example robber

a = ["Totally not evil stuff", "Hello World!"][0]
print(a)


Deleting the 1 at the end of the first line prints the target string.

## Questions for Meta:

• Which original and transformed strings should I use?
• Is this a duplicate?
• This could be kind of difficult to write a cop for that doesn't just rely on someone brute forcing it – Redwolf Programs Apr 11 at 0:21
• @RedwolfPrograms Hmm, you're right. I guess just saying "pls don't brute force" wouldn't work. Maybe instead of a string, submissions could implement a mathematical function? You wouldn't be able to verify, say, cosine using just brute force. – user Apr 11 at 0:23
• That could be really cool actually. If you had a variety of ones like sqrt, tan, factorial, sum of proper divisors, and so on it would be a lot of fun. – Redwolf Programs Apr 11 at 0:30
• @RedwolfPrograms Only problem would be that there wouldn't be any more traitors to root out :( I made the challenge just for the title – user Apr 11 at 0:46

# Exchange of money in least notes

Suppose A and B are two good friends. A has borrowed $$\n\$$ dollar from B. Now B wants the money back from A and A is also ready to give it. But the problem is A has only $$\x\$$ dollar notes and B has $$\y\$$ dollar notes. They both want to keep the number of notes in exchange as low as possible.

As an example if $$\n=37\$$, $$\x=5\$$ and $$\y=2\$$, then the least amount of notes in exchange will be nine 5 dollar noted from A then four 2 dollar notes from B will make 37. This solution is found through brute forcing with a python program.

Here in the challenge your input will be values of $$\n, x, y\$$ and output should be the least of amount of notes as possible for A, B. A will give notes first and B later. Input and output seperator can be anything, no leading zeros in input numbers, no negative numbers in input. Standard loopholes apply and shortest code wins.

Test Cases

37 5 2 -> 9 4
89 3 8 -> 35 8
100 12 7 -> 13 8

• I'm almost certain there's a closed form solution to this, and if not one that's very close to closed form. – Redwolf Programs Apr 12 at 4:57
• Is it guaranteed that the given values of $n$, $x$ and $y$ lead to a valid solution? E.g. there's no solution for $n=21$, $x=6$, $y=4$. – Delfad0r Apr 12 at 8:22
• @Delfad0r input is guaranteed to valid – Wasif Apr 12 at 8:23

# A large number of stamps code-golfinteger-partitionsarithmetic

I have a large number of stamps of several different values. It's really annoying when I can't make a total exactly, so please write me some code to help me with this.

Your challenge is to make a function or program that takes an arbitrary number of integers as input and returns the largest integer that can't be made by adding several of those, repeated as many times as you like. For example, 22 can be made with 5 and 7 with $$\5+5+5+7\$$.

If there is no answer (there are always more you can't make), e.g. you are only given even numbers, you can return anything that's not a positive integer or error the program.

Input will never include 1.

# Testcases

5,7 => 23
3,5,6 => 7
6,9,12,15 => FALSE
45,91 => 3959


Note: for two values x and y the result is $$\xy-x-y\$$ - You may find this helpful.

# Scoring

This is , shortest wins!

# Meta

Is this clear?

I feel like just two arguments would result in tiny trivial programs using the specified formula.

How should this be tagged (aside from code-golf)?

Please can I have some more testcases?

• Related – pxeger Apr 13 at 10:37
• @pxeger But different. – A username Apr 13 at 10:46
• Is 1 promised not inputted? – l4m2 Apr 13 at 12:54
• I think [integer-partitions] would apply here, as would [arithmetic] – caird coinheringaahing Apr 13 at 15:03
• @l4m2 Yes, input won't be 1. – A username Apr 13 at 20:44
• @cairdcoinheringaahing probably – A username Apr 13 at 20:44
• I would suggest change falsy value to any values wont be ambiguous. For example, 0 should work here. While some languages (Lua for example) consider 0 as truthy. – tsh Apr 14 at 3:40
• @tsh Ok, anything that's not a positive integer. – A username Apr 14 at 4:31

# Basic Typescript Types

• suggested testcase: string | string, number & number – tsh Apr 14 at 10:15
• @tsh I just posted the question, thanks for the suggestion, I'll add the testcases there. – Etheryte Apr 14 at 10:17

# Matching to Homologous group

• 1. The underscore doesn't really seem necessary to me since there can't be any other syntax. 2. Can we assume the input will always be one of those categories? If not, add some test cases, and clarify the possible elements/other syntax that might be in the input. 3. Add classification tag? 4. Will you allow output as any 6 distinct values (not saying it has to be, but some challenges do allow this to remove the part of compressing some strings), or does it have to be those strings? If so, do they need to be capitalised exactly like that? – pxeger Apr 11 at 16:15
• @pxeger the input is guaranteed to be in 6 categories. Classification tag added. About the underscore i'll think later. And output needs to be exactly capitalized like in question. Thanks! – Wasif Apr 11 at 16:18
• Also maybe add some more test cases with larger numbers (more than 1 digit)? And clarify what integer syntax is allowed (areleading zeroes allowed, can the number be <2)? – pxeger Apr 11 at 16:21

# It seems $$\2^n\$$?

Let $$\a_0=1\$$ and $$\a_{i+1}=1+\sum_{j=0}^ia_i\$$, then $$\a_i=2^i\$$, which is no fun.

Now we reverse half of the value, $$\a_{i+1}=L(1+\sum_{j=0}^ia_i)\$$ for odd $$\i\$$, where $$\L\$$ reverse the number, e.g. 15=>51, 1230=>321.

Solve $$\a_i\$$. You can choose 1-index, or reverse each output(output $$\L(a_i)\$$).

First elements

1,2,4,8,16,23,55,11,121,242,484,869,1837,4763,8437,47861,64735,74921,204391,287804,696586,2713931,4107103,6024128,14238334,86667482,115144150,3882032,234170332,466043864,934384528,6509678681,8378447737,47459865761,64216761235,74225334821,202658857291,285417713504,690735428086,2716580741831,4098051598003,6006913016918,14203016212924,84852423060482,113258455486330,66279019615622,292795930588282,465671168195585,1051263029372149,8924478506252012,11027004564996310,2629992190045022,24684001320037642,48257004620086394,97625007260161678,653323025410052591,848573039930375947,4981570689706417961,6678716769567169855,1793343193533475331,15150776732667815041,28003653356435510303,58305206821771140385,77082245346314016611,193692658989856297381,267495217979713583783,654880535959426178545,907532588191701679031,2217293660110554036121,2422708011220237854344,6857295331441345926586,27135819628826609541731,40850410291709301394903,60898720681438502800718,142599541264857105590524,840181112417925280991582,1125380194947639492172630,625434898725989830670522,2876195288621268815015782,4651300367352427750932575,10403690944594965380964139,87282916703998198818370802,108090298593188129580299080,61895061952673681795081612,278075659139049940955679772,445953119188990872813151655,1002104437467090754724511199,8932209449051814394788024002,10936418323985995904237046400,829047480819917974663827812,22701884128791909783137920612,42214857266591838575286730454,87618625524175658141562571678,653341521382613153840152732571,828578772430964470123277875927,4581575556420498291684457517561,6238733101282427231931013269415,3883562026836445846520266477421


• 1) You should make it clear whether we need to print the $i$'th term, or the first $i$ terms or we can print the infinite sequence. Usually challenges like these allow all of these options. 2) Can you clarify what does "reverse each output" mean? So instead of $a_i$, the solutions can also print reverse of it? 3) There also needs to be a winning criterion. – Manish Kundu Apr 19 at 7:39

# Close neighbours stick together

• I felt like I'd done this at some point but couldn't find anything in my last 100 or so answers... I think it's a good easy level problem. – Jonah Apr 18 at 20:53

# Posted ;)

• So this is just abs(x-y), since I can just represent the days using integers? Doesn't seem very interesting – pxeger Apr 14 at 9:32
• I think restricting the input to being one of the 7 days (maybe in whatever consistent case answers want) would be a better version of this – caird coinheringaahing Apr 14 at 9:57
• Won't this be simple (x-y+7)%7? – tsh Apr 14 at 10:26

# Posted

• The idea seems to be compute an actually valid rule to replace the flawed schoolroom heuristic, and do so by means of a golfed algorithm. Given that goal, I think it would be easier to work with a word list of all correct words. Then the task is: "Your input will be a word from that list, either or unaltered or with the ie or ei transposed. Return true if unaltered, false if transposed" – Jonah Apr 18 at 18:33
• @Jonah I've edited the task with your suggestion. I hope this makes it less confusing. – dingledooper Apr 18 at 20:49
• Thanks. It's clear to me now and an interesting challenge. I suspect rather tough to golf well too. – Jonah Apr 18 at 20:52

# Plz Halp, Need Investors ASAP

• This might be a duplicate, but searching is going to be difficult because of how many ways you can describe the challenge. One thing that might make it interesting is giving each investor an amount of money they'll invest, then have the programs maximize the money invested (for example, by skipping three meetings with investors promising $1 and going to a single meeting with an investor who promises $10). – Redwolf Programs Apr 26 at 19:00
• The thing about that is that the algorithm gets a lot harder - I'm pretty sure you need DP to solve your variant. Also, I did spend quite a while looking for any duplicates and could not find any. – knosmos Apr 26 at 19:07

# Number to set - duplicate

• Dupe – caird coinheringaahing Apr 27 at 18:36
• aw rats, but thank you – Wzl Apr 27 at 18:37

# Decompress a Sparse Matrix (WIP)

The dual of this challenge

Decompress a sparse matrix reversing the method here Compressed sparse row (CSR, CRS or Yale format).

There will be 4 inputs, either as separate variables or as a list of lists:

• V, a list of the nonzero elements of the matrix in row-major form. This is of length NNZ (the number of nonzero elements in the original matrix)
• NCOLS - the number of columns in the original matrix.
• JA - a list of the column indices of the elements in V, also of length NNZ. (zero-indexed)
• IA - a list that yields the number of nonzero elements in each row. IA[0] = 0, IA[i] = IA[i - 1] + <number of nonzero elements in row i>. The number of nonzero elements in row i is IA[i + 1] - IA[i].

Input will be a list of 3 lists and the number of columns in the original matrix, e.g. either

[
[5, 8, 3, 6],
[0, 0, 2, 3, 4],
[0, 1, 2, 1],
4]
]


Or

V = [5, 8, 3, 6]
NCOLS = 4
IA = [0, 0, 2, 3, 4]
JA = [0, 1, 2, 1]


Output will be a decompressed matrix/list of lists:

[[0 0 0 0],
[5 8 0 0],
[0 0 3 0],
[0 6 0 0]]


If your language doesn't support actual data structures, input and output may be text.

# Test cases

Input 1:

[ 5, 8, 3, 6 ]
[ 0, 0, 2, 3, 4 ]
[ 0, 1, 2, 1, ]
4


Output 1:

[[0 0 0 0],
[5 8 0 0],
[0 0 3 0],
[0 6 0 0]]


Input 2

[ 10 20 30 40 50 60 70 80 ]
[  0  2  4  7  8 ]
[  0  1  1  3  2  3  4  5 ]
6


Output 2:

[[10 20 0 0 0 0],
[0 30 0 40 0 0],
[0 0 50 60 70 0],
[0 0 0 0 0 80]]


Input 3:

[ ]
[ 0 0 0 0 ]
[ ]
3


Output 3:

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


Input 4:

[ 1 1 1 1 1 1 1 1 1 ]
[ 0 3 6 9 ]
[ 0 1 2 0 1 2 0 1 2 ]
3


Output 4:

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


Input 5:

[ 5, -9, 0.3, -400 ]
[ 0, 0, 2, 3, 4 ]
[ 0, 1, 2, 1, ]
4


Output 5:

[[0 0 0 0],
[5 -9 0 0],
[0 0 0.3 0],
[0 -400 0 0]]


Assume inputs may contain any real number, you need not consider mathematical symbols or exponential representation (e.g. 5,000 will never be entered as 5e3). You will not need to handle inf, -inf, NaN or any other 'pseudo-numbers'. You may output a different representation of the number (5,000 may be output as 5e3 if you so choose).

# Scoring

This is a , fewest bytes wins.

• I'd suggest to at least briefly explain how the decompressing works in the post. The challenges should be self-contained as much as possible. – Bubbler Apr 22 at 23:55
• @bubbler, that's coming, but I need to figure out how to do that/explain it myself. I've left (WIP) on the question because of this. – Pureferret Apr 23 at 0:11
• @Pureferret I think it would be better to allow only nonzero integers instead of any real number. It'd be easier for most languages that way – user May 2 at 20:59
• @user I think it's more interesting seeing those languages work around those difficulties. Also the original challenge required them, so it I my makes sense this one does too. – Pureferret May 2 at 21:14
• @Pureferret I'm not sure many golfing languages support arbitrary precision floating point numbers. Would they be able to use strings, then? Edit: could you at least restrict it to rational numbers? Unlike Jon Skeet, most of us here don't know all the digits of pi :P – user May 2 at 21:17
• @user it needn't be arbitrary, just as long as it matches the test cases – Pureferret May 2 at 23:46
• You do need a objective winning criterion. See why here. Nice challenge though! Probably simplest to just make the criteria [code-golf]. Most [code-golf] challenges don't result in an accepted answer though, so you should be fine. – A username Apr 29 at 12:48
• @ausername Thanks for the feedback, I'll work on the winning criterion – EliteDaMyth Apr 29 at 12:51
• You don't need the last part, by the way. It's usually implied. – user Apr 29 at 19:30
• @user according the the comment above, the person said this needed a Winning Criterion thats the reason i added it. – EliteDaMyth Apr 29 at 19:55
• Sorry, I meant just the last sentence. Also, you don't need to make "Winning criterion" a separate header. – user Apr 29 at 20:05
• @user Alright, gonna remove it – EliteDaMyth Apr 29 at 20:08

# Self-Interpreter But Never Loops

I'm afraid that this might look too intimidating. Is there any way to improve it?

Ever since Gödel and Turing, it is widely assumed that a reasonable programming language that contains a self-interpreter can never be terminating. Here, I present a simple proof.

Suppose that, on the contrary, a total language has a self-interpreter eval(program, input) that accepts two natural numbers that encode programs and inputs, respectively. Then this function eval can be encoded as a natural number, since it is a program with two inputs. We define the function

evil(n) <- 1 + eval(n, n)


Then, since evil is a program, it can be encoded as a number EVIL. Therefore evil(EVIL) = 1 + eval(EVIL, EVIL). By the nature of eval it computes to 1 + evil(EVIL). But this is impossible, since no natural number is equal to one plus itself. Therefore, somewhere along the line of reasoning, one of the functions involved must loop indefinitely.

[On the other side, the program can also return something like StackOverflow or null, but that would render the self-interpreter incorrect, since the program that is being interpreted actually behaves differently.]

Of course, such a proof ignores a bunch of details -- in imperative languages, the function can change global variables; some nasty languages doesn't have anything like functions; some languages may not be able to define natural numbers, etc. But you get the idea. I quote C. T. McBride:

It's ironic, but not disastrous that lucifer, the evaluation function by which [...] angels [representing programs in a terminating subset of Haskell] bring their light, is himself an angel, but one who must be cast into Hell.

Now it's time for rebellion.

Challenge. Pick your favorite language (or a subset of it) that is terminating. Write a self-interpreter for it. The language must also contain (to eliminate trivial cases):

• Arithmetic for arbitrary precision integers.
• A program that always returns its input.
• Random-access lists.
• The encoding of programs must support random access. There must be a program that enumerates all legal programs up to size n, where n is the input.

What's happening here? Indeed, there are flaws in our reasoning above. A self-interpreter need not have its program encoded with natural numbers. And moreover, with an modestly elaborate type system, you can forbid the evil program to be well typed, as pointed out here. The linked paper already contains a program that fulfills the requirements of the challenge in the language $$\\mathrm F_\omega\$$ (arithmetic for integers and random-access lists are left as an exercise for the reader).

• so, a halting language plus an extra exec program? – l4m2 May 2 at 2:34
• @l4m2 Basically yes. – Trebor May 2 at 4:54

# Tips for golfing in Binary Lambda Calculus

• No, you don't need to post [tips] questions (especially these kind) in the Sandbox. Feel free to just post to main :) – caird coinheringaahing May 1 at 17:47
• Thanks for sandboxing this, though! It's nice to see new users using the Sandbox instead of directly posting to main - always better to be on the safe side. – user May 1 at 17:50
• @caird Wow! Thanks for the quick reply. Posted. – Andrew Li May 1 at 17:53
• I've edited this down to a stub now that it's been posted to save space – caird coinheringaahing May 1 at 17:55

# Base-ically god

• I've edited this down to a stub now that it's been posted to save space – caird coinheringaahing May 1 at 18:12

# Generate the ticks of a graph

• yes I need something like this. +1 because clearly specified and the gif demonstrates the different testcases well – lyxal May 1 at 5:30

# Assassin KoTH

## Description

Each bot is a point in the 2D plane. Each game, the list off bots is shuffled and each bot is a particular bot as their mark. This is done such that there is a cycle of assassins and targets.

Each bot's goal is to kill their mark and avoid their assassin. They can kill their target by getting within a certain distance to them. When they kill their target their new target is their target's assigned target. This continues until there are two bots left in the arena. Then each bot scores their kill count and the two remaining bots score their kill count plus a bonus.

## Sandbox

• What should the bonus for being one of the remaining bots be?

• Should the game take place on a grid instead of a 2D plane?

• Should there be a time limit?

• Is creating a bot accessible enough or is the game too complicated?

• Any other feedback?

• I think the bonus should be the number of bots in play. – StackMeter May 3 at 9:00
• @StackMeter Wouldn't that heavily bias the game in favour of camping? Getting kills and dying early should still be a viable strategy. – EnderShadow8 May 3 at 9:19
• Yeah, I see what happens what that in place: maybe you get double your score, so campers get 0 if they last to the end (0 * 2 is still 0). – StackMeter May 3 at 9:52
• @StackMeter Camping still needs to be a viable strategy though - more variety is better. – EnderShadow8 May 3 at 10:32
• 50*(kill/total bot)+survival bouns(5) or something similar. – okie May 10 at 1:41