Sandbox for Proposed Challenges

Question

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

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Other

Search the sandbox / Browse your pending proposals

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Answer 1

Studio 54

code-golf decision-problem number

Studio 54 was a famous nightclub in Manhattan. The club is referenced in the Futurama episode Rebirth in which the crew visits a nightclub called Studio 1²2¹3³. The mathematical expression 1²2¹3³ evaluates to (1 x 1) x (2) x (3 x 3 x 3) = 1 x 2 x 27 = 54.

Challenge

Determine whether a positive integer is a "studio number." We define a studio number to be a number n that can be expressed as the product of a set of distinct positive integers that does not include n, each of which is raised to the power of one of the numbers in the set. Or, more mathematically:

You should have a consistent output value for "is a studio number" and "is not a studio number," and nothing else.

Test cases

These are inexhaustive lists and are just meant for basic ad-hoc testing.

Studio numbers:

4
12
16
18
52
54
64
68
72
88
96

Not studio numbers:

1
2
9
10
11
42
53
55
69
77
87
90

Computed by this script.

Sandbox

I'm going off of this for the two consistent outputs, but I'm not really sold either way. I could also change the requirements to be to output the "studio" representation of the number.

Does the math-y bit help? Could I make the studio number definition clearer?

I've been unable to find any "nice" properties of these numbers that allow for methods besides brute force. Would this still be interesting enough to golf? I could also add a "reasonable time" limit that would enforce some non-naive code to reject bad attempts, but I'm not sure that's much better.

The studio numbers do not appear to be a sequence recorded on the OEIS.

Answer 2

Only HeLlO WoRLd is allowed.

We are all familiar that "Hello World" is the 1st introductory program that most people learn when they first start to program. Then programmers go on to greater and better programs. But who says they have to go on to greater and better programs? What if all other programs were censored?

Your Task:

Write a computer program that takes in standard input. If the standard input is any case-insensitive version of HeLlO WoRLd, do nothing. If the Standard input is anything other than a case insensitive HeLlO WoRLd, print an infinite loop of a HELLO WORLD matrix to the standard output.

To print an infinite HELLO-WORLD-Matrix, randomly sort the letters of "HELLO" and the letters of "WORLD", join the two words with a space as if you were saying HELLO WORLD, although you are probably saying "HELLO DWROL", " OELLH LWODR" gibberish with an occasional "HELLO WORLD". Then just keep printing all this gibberish to the standard output.

ELHOL WRDLO     HOELL LDWRO     LOELH DLWRO     EOLHL DRLOW     LHELO OLRWD     

OLELH LODRW     EOHLL LWROD     LLOHE OWDRL     HLLEO OLRWD     LEHOL LOWDR  

OLLHE WROLD     OLEHL DLRWO     OHLEL OWDLR     LLHEO OWDRL     LLEHO ROLWD     

HELOL WLORD     HLOLE LWODR     LHOEL ODLWR     OLEHL DWORL     LLHEO OWDRL     

LHOLE WORDL     LOLHE WLODR     HLLOE WRODL     HOLLE LDORW     EOLHL WODLR  

ELOHL DRWLO     LHELO LRDWO     HLOEL RLDWO     LHOLE DOWLR     OLELH DOLWR     

OLLEH WORLD     LHLOE RWLDO     OELLH LWODR     LEHLO DOLRW     EOHLL DWRLO     

HELLO WORLD     LOLEH ODWRL     HOLLE WDLOR     LHEOL LORWD     LLOHE OLDWR     

OHLLE DRLOW     LOEHL LODWR     OHLLE ODRLW     HOLEL LWDRO     HOLEL DWROL  

ELOLH RWOLD     EOLHL WDLOR     LHOLE WRODL     HLLEO ODLRW     HLELO LDWOR     

HLELO WLDRO     HLLOE DRWLO     HOLEL OLWRD     OELHL WORDL     HOELL LDRWO     

LLEHO WORLD     OLELH DLOWR     OLHEL LDWRO     ELOLH DWROL     EHLLO WDLRO  

OLELH LDROW     LHEOL WORLD     OLEHL LWDRO     OELHL RWLOD     LEOLH RWOLD     

HLOLE DRLOW     LOELH RWLOD     LHELO LODWR     LLOHE LWDRO     LOEHL OWDLR     

LEHOL WORDL     OLEHL RWLDO     LOELH LOWDR     HEOLL LODRW     HLOLE RLODW  

LLEHO DWORL     LLOHE DWOLR     LLHEO RODWL     OLLEH DLWOR     LHEOL ORDWL     

HLEOL OWDRL     LELOH LDROW     HELLO LDWRO     HOELL ODWLR     OEHLL ROWDL     

EHOLL WRLDO     HLOLE WRLDO     LLHEO WDRLO     LOLEH OLDWR     OEHLL RLWDO  

OELHL DLORW     LLHEO RDWOL     HLLOE OLDRW     OLLHE LRODW     OELLH LDROW     

LEHOL LOWDR     LEHLO DRLOW     HOLEL WROLD     LHELO LORWD     EHLLO LWODR     

HLOLE OLRDW     LOLHE OLRWD     LOLHE DORWL     LOHEL WDLRO     OHELL RWOLD  

LEHLO RLWDO     HLEOL LWRDO     OELLH LWORD     HELLO LDROW     OLHLE LWDRO 

 

There is actually only one "HELLO WORLD" amid all this gibberish

Winning criterion: shortest program in bytes.

Answer 3

Golfing a Busy Turing Machine

code-golf turing-machine busy-beaver

For the sandbox

This question is really hard, and the solution is restricted to one "language" – a 1-tape, 2-symbol Turing Machine. So I'm not sure if it belongs on PPCG. I've written up a basic description below, but can go into more detail if anyone is interested.

Question

I recently came across a paper that explicitly presents a 7910-state 1-tape, 2-symbol Turing machine that cannot be proven to run forever in ZFC, assuming ZFC is consistent. It also cites codegolf.stackexchange.com!

The existence of this Turing machine proves that calculating BB(7910) is independent of ZFC.

So, we know that we can calculate up to at least BB(4), and definitely can't calculate BB(7910) and above.

Can you create a Turing Machine with under 7910 states that cannot be proven to run forever in ZFC?

The author designed two custom-purpose programming languages (Laconic and TMD) to create this Turing Machine. In order to improve upon his work, I imagine you could go one of three ways:

1. Optimize his algorithm in Laconic such that it encodes the interpreter or Friedman's mathematical statement (section 3.1) more tersely.

2. Optimize TMD so individual instructions are translated to fewer states.

3. Find a simpler statement whose truth implies the consistency of ZFC, and encode that instead of Friedman's statement.

4. Go another direction entirely!

Winning criteria

The Turing Machine with the fewest number of states that cannot be proven to run forever in ZFC, wins. The length of the code you used to generate this Turing Machine is irrelevant.

You don't win if you compute BB(5), but you do get eternal fame.

Answer 4

Grouped Keyboard Scores

code-challenge

In the above graphic, one can see 12 distinct color groups, which roughly correspond to columns on a keyboard. The following is a plaintext representation of which characters occur in each group.

Group 1:  ~` \n\t
Group 2:  !1QqAaZz
Group 3:  @2WwSsXx
Group 4:  #3EeDdCc
Group 5:  $4RrFfVv
Group 6:  %5TtGgBb
Group 7:  ^6YyHhNn
Group 8:  &7UuJjMm
Group 9:  *8IiKk<,
Group 10: (9OoLl>.
Group 11: )0Pp:;?/
Group 12: _-{["'+=}]|\

Challenge: Sort characters in the input according to their position in the aforementioned table. For input "Hello, World!", the output would be " !WedrH,llool". The relative order of characters within the same group does not matter, so the output " !WderH,llloo" is just as acceptable.

Scoring: Let P be the product of the number of characters in each non-empty section. Let S be the number of sections your program uses. Then, your score is P × S.

For example, the program QAZ would have a score of 3, and QWERTY would have a score of 6. 12321 would have a score of 12. The lowest such score wins.

Here is a code snippet for scoring your submission:

var sections = [
    "`~\t\n ",
    "!1QqAaZz",
    "@2WwSsXx",
    "#3EeDdCc",
    "$4RrFfVv",
    "%5TtGgBb",
    "^6YyHhNn",
    "&7UuJjMm",
    "*8IiKk<,",
    "(9OoLl>.",
    ")0Pp:;?/",
    "_-{[\"'+=}]|\\"
];

function getSection(chr){
    for(var i = 0; i < sections.length; i++){
        if(sections[i].indexOf(chr) >= 0){
            return i;
        }
    }
    return -1;
}

function score(program){
    // group by sections
    var sectionHolder = [];
    var foundSections = [];
    for(var i = 0; i < program.length; i++){
        var chr = program[i];
        var index = getSection(chr);
        if(index < 0)
            return "n/a\nInvalid character: " + chr;
        
        if(!sectionHolder[index])
            sectionHolder[index] = [];
        
        sectionHolder[index].push(chr);
        
        if(foundSections.indexOf(index) < 0)
            foundSections.push(index);
    }
    
    var S = foundSections.length;
    var P = foundSections.map(function(e){
        return sectionHolder[e].length;
    }).reduce(function(a, c){
        return a * c;
    }, 1);;
    
    return S * P;
}
var output, code;
window.addEventListener("load", function(){
    output = document.getElementById("output");
    code = document.getElementById("code");
});
function update(){
    output.innerHTML = "";
    output.appendChild(document.createTextNode(
        "Score = " + score(code.value)
    ));
}

* { font-family: Consolas, monospace; }
#output { white-space: pre; }

<textarea id="code" oninput="update();"></textarea>

<div id="output"></div>

Test cases

Note: ␉ represents a tab and ␤ represents a newline.

 "input" => "output"

 "Hello, World!" => " !WedrH,llool"
 "Grouped Keyboard Scoring" => "  aSededcrrrGbgynuKiooop"
 "QWERTYUIOPqwertyuiop" => "QqWwEeRrTtYyUuIiOoPp"
 "2017 + 42 = something" => "    122se4tghn7mio0+="
 "Tab␉ulator" => "␉aarTbtulo"
 "Hello␤World" => "␤WedrHllool"

Answer 5

Call a library function

Given a single int32, a path to a Dynamic Link Library (.dll) or Shared Library (.so), and the name of a function, return the single int32 result of calling the function on the single int32.

Examples

On 64 bit Linux: 0 /usr/lib64/libm-2.24.so fesetround → 0

On 64 bit Linux: 1 /usr/lib64/libm-2.24.so fesetround → 1

On 32 bit Linux: 1023 /usr/lib/libm-2.24.so fesetround → 1

On 32 bit Linux: 1024 /usr/lib/libm-2.24.so fesetround → 0

On 64 bit Windows: inp please\edit\filename.dll fname → out

On 64 bit Windows: inp please\edit\filename.dll fname → out

Answer 6

What is the maximum number of backslashes (escape characters) required to mean one backslash?

If you want to use a regex to look for a backslash, you have to escape that backslash, so that the character after it isn't escaped instead. But if you then have to store this regex in a string (in a c-style language, for instance), you need to double the number of backslashes, so that a regex string to match \stuff\ would need to be "\\\\stu(f+)\\\\" (and I had to further double the backslashes to post it in StackOverflow, but that isn't executable so doesn't count).

In your answer, explain the language and the (reasonable) situation, from either real or made-up business needs, and the answer with the most backslashes (per final, output backslash) will get upvoted (permanently) and accepted (until a better one comes along). If using AutoHotKey or another language that has a different escape character (for instance, `), then instances of that character will count instead of backslashes.

This question is not how many backslashes could you use in some esoteric code-golfing language to eventually calculate to a backslash, otherwise I don't think there would be an upper limit. This instead is about feasible scenarios that force you to use a lot of backslashes.

Answer 7

Write an interpreter for XKCD's broken language

code-golfinterpretercode-challenge

---

Meta

• Is this a good idea?
• Is the point system good?
  • If so, are the point values good? I based them off of how difficult I imaged each part to be.

Overview

Randall Munroe, author of the webcomic XKCD, posted a comic a while back about a joke programming language and how it gets types confused.

Here's the comic in question

Your job is to write an interpreter for a slightly modified version of this language.

Rules

• If your language supports it, it must be a live interpreter where all input lines start with [#]> (where # is the line number) and all outputs must start with =>.
  • If your language does not support it, you may substitute this with reading all the lines on the input and printing out each output on its own line, still starting with =>. Remember to keep track of line numbers.
• All commands must be usable in any order and with any parameters (within reason)
• Each command you implement correctly is worth the listed point value. See scoring to find your final score.

Integers plus numeric strings (1 point)

Given an int and a string containing a number (in that order) calculate the numeric sum of them, then return the result as a string with quotes surrounding it.

[1]> 2 + "2"
=> "4"
[2]> 6 + "13"
=> "19"

Numeric strings plus lists (1 point)

Given a numeric string and a list, append the numeric value to the list and return the list as a string.

[1]> "3" + []
=> "[3]"
[2]> "7" + [1,4]
=> "[1,4,7]"

Dividing by zero (1 point)

Any number divided by zero returns a NaN object. This does not have quotes around it.

[1]> 1/0
=> NaN

NaN plus integer (2 points)

Given a NaN object and an integer, pretend it's a string and increment the leading character, carrying over if needed. The result does not have quotes.

[1]> (5/0)+2
=> NaP
[2]> NaN+256
=> NbN

You do not need to use ASCII for this, any character set works, as long as it includes at minimum the 52 uppercase and lowercase letters.

You will never have to add a result from this to another integer. (For example, NaP+4 is invalid)

String plus string (1 point)

Given two strings, remove swap the first and last quotes with single quotes and return the result.

[1]> ""+""
=> '"+"'
[2]> "Hello"+"world"
=> 'Hello"+"world'

List of integers plus integer (3 points)

Given a list of integers (or an empty list) and another integer, return True or False based on whether the new integer matches the linear pattern.

It will follow this rule:

If the list has 0 or 1 items, return True regardless (everything matches).
Determine the pattern of the list by subtracting every item by the item right before it. If the pattern is inconsistent, return False regardless (nothing matches).
Otherwise, check if the new integer matches the pattern. If it does, return True. If it doesn't, return False.

[1]> [1, 2, 3, 4] + 5
=> True
[2]> [5, 7, 9, 11] + 13
=> True
[3]> [6, 5, 4, 3] + 2
=> True
[4]> [2, 4, 6, 8] + 9
=> False
[5]> [1, 2, 1, 4] + 5
=> False

Range(a, b) (1 point)

With the Range function given two numbers, return a list of numbers from a to b.

[1]> Range(1, 5)
=> [1, 2, 3, 4, 5]
[2]> Range(3, 6)
=> [3, 4, 5, 6]
[3]> Range(6, 4)
=> [6, 5, 4]

Plus integer (1 point)

Given simply "+" and an integer, return the line number plus the integer.

[1]> +2
=> 3
[2]> +2
=> 4
[3]> +1
=> 4

Single digit plus single digit (2 points)

Given two single digit integers a and b, replace all future instances of a in the output with (a+b)%10 (where % means modulo, essentially wrap around if the result is more than 1 digit). Return Done. This effect is superficial and has no effect on math. This only affects output, not input.

[1]> 3+2
=> Done
[2]> Range(1, 6)
=> [1, 2, 5, 4, 5, 6]
[5]> 1+2
=> Done
[4]> Range(1, 6)
=> [3, 2, 5, 4, 5, 6]

Floor (1 point)

Draw an ascii art floor with the number at the bottom. The specifications are 3 lines of only pipes, then a line with a pipe, 3 underscores, the number, and 3 underscores.

[1]> Floor(4.7)
=> |
=> |
=> |
=> |___4.7___
[2]> Floor(105.3)
=> |
=> |
=> |
=> |___105.3___

Scoring

Add up the points you've earned. Your score is now calculated as (15-points) * bytecount. Lower is better.

Notes

• You do not have to account for mixing functions. For example, Range(Floor(2.3)) is invalid.
• Whitespace may be added or removed as is convenient.
• Double quotes or single quotes may be used as convenient (as long as you use the opposite for "String plus string")
• Any brackets may be used for lists, as long as it's consistent.
• A few commands were omitted from the original comic because I couldn't figure out a way to make it well specified.

Answer 8

Counting from 0 - 100

I posted this question, but it was not taken very well, so I wanted to put it through the sandbox and get some feedback/help before re-posting.

Challenge

Output all numbers from 0-100. Without using any of your languages built in loops.

Loops that are not allowed

This list contains, but is not limited to

• For loops
• While loops
• Do While loops
• Goto Statment
• In Range

Rules

• This is code-golf the shortest solution in bytes wins
• Standard Loopholes Apply
• You may use functions as well as programs

Answer 9

OCR

test-battery code-challenge

In this challenge you will attempt to write a program to perform OCR in the fewest bytes possible. The tests are linked below, the only data that your program receives is the contents of the image, you may not rely on file name, timestamp, or other metadata, additionally you may not query any external source such as the internet or dispatch an independent program to outsource the task of OCR.

Spec

Given a hand written word in in image of 80px in height. Output the word. words will consist of lowercase latin letters:

abcdefghijklmnopqrstuvwxyz

Scoring

Given the test cases, your score is a percent of the words you have gotten correct. No partial credit.

---

Tests cases:

TODO

Answer 10

Data exfiltration

Frenzy in the frequency domain.

Summary of the challenge

You must find a way to broadcast a ten-character password through a lossy communication channel and recover the password on the other side. To achieve this you must write two programs. The first program will receive the password as input and encode it as output data for the channel, the second program has to decode the output of the channel back to the password.

Some background

In signal processing theory, many problems are usually dealt with by converting a signal from the time domain to the so-called frequency domain, a trick that relies on the fact that any function can be written as an infinite series of sine waves. Signals can be converted into this domain using a Fourier transform. This transform is lossless, and the resulting signal can be converted back into the time domain using the inverse Fourier transform. The frequency domain has some interesting properties, as the actual values of the signal in it represent the amplitude and phase of different frequencies in the original signal.

A special case exists for when the signal exists out of equally spaced sampled points, called the discrete-time Fourier transform. To perform this transform the fast fourier transform algorithm is commonly used. Given a signal of N samples spaced with dt spacing, it will convert it into a signal containing N frequency bins which are each 1/(N*dt) apart.

Channel definition

The communication channel requires 256 unsigned bytes data as input, and returns 256 unsigned bytes data as output. If the input values are centered around zero and interpreted as data samples on regular intervals, then the output values represent the amplitude of the signal in the frequency domain scaled to use the range 0 to 255, calculated using a discrete fourier transform. The channel is lossy as it only transfers the amplitude of each frequency, not the phase.

It can be simulated using the following python 3 script:

import cmath
def channel():
    # amount of input and output values
    l=256
    # read the input values from standard input as newline separated integers and center them around zero
    n=list(map(lambda: min(255, max(0, int(raw_input())))-127.5, range(l)))
    # perform a discrete fourier transform
    v=[sum(v*cmath.exp(-2.0j*cmath.pi*t*k/l)for t,v in enumerate(n))/l for k in range(l)]
    # remove artifacts due to the Nyquist limit
    v[1:128]=map(lambda n:n*2,v[1:128])
    v[129:]=[.0]*127
    # return the scaled magnitude of each frequency bin
    for i in v:print(int(round(abs(i)*cmath.pi/2)))

Input/Output

The password is randomly generated using only using visible ASCII characters (0x20 up to and including 0x7E) and is 10 characters long.

Inputting the password to the encoder, communicating it to the channel, receiving data from the channel and communicating the decoded password should all follow the default input/output rules. The password must be decoded only from data received from the channel, no side-channels are allowed.

Scoring

This is code-golf, where the score is calculated by adding the length of both the encoder and decoder program. For each language, the shortest entry in bytes wins.

Meta

• Is the challenge clear
• Is the difficulty okay
• Anything else?

Tags: code-golf

Answer 11

List My Factors!

code-golfmath

---

Introduction

Given an algebraic expression as input, list all the factors of it. A factor of an algebraic expression is any algebraic expression (or simply a numerical expression, sometimes) that evenly divides it. A factor can only be an integer or an algebraic expression consisting of integers and variables.

---

Rules

• The algebraic expression will contain * to denote multiplication.

• The algebraic expression will only contain integer constants and coefficients.

• The algebraic expression will contain ^ to denote exponentiation.

• The algebraic expression will only contain positive constants, coefficients and variables.

• Your program should output only the positive factors.

• The algebraic expression will not contain negative exponents.

• You must not use any built-in to accomplish this.

• Standard Loopholes apply.

---

Examples

The algebraic expression 5*x^2 has the following factors:

1. 5
2. x
3. x^2
4. 5*x^2
5. 5*x
6. 1

The algebraic expression 10*(x-y)^2 has the following factors:

1. 10
2. 5
3. 2
4. 1
5. (x-y)
6. (x-y)^2 or x^2 + y^2 - 2*x*y
7. 2*(x-y)^2 or 2*(x^2 + y^2 - 2*x*y) or 2*x^2 + 2*y^2 - 4*x*y
8. 5*(x-y)^2 or 5*(x^2 + y^2 - 2*x*y) or 5*x^2 + 5*y^2 - 10*x*y
9. 10*(x-y)^2 or 10*(x^2 + y^2 - 2*x*y) or 10*x^2 + 10*y^2 - 20*x*y.
10. 10*(x-y) or 10*x - 10*y
11. 2*(x-y) or 2*x - 2*y
12. 5*(x-y) or 5*x - 5*y

The algebraic expression x^2 - y^2 has the following factors:

1. 1
2. x-y
3. x+y
4. x^2 - y^2

---

Input

Your program may take the input in any way except assuming it to be present in a predefined variable. Reading from file, input box, modal window, command line etc. is allowed. Taking input as function argument is allowed as well.

---

Output

Your program should output a list of factors of the given input as a collection data type (such as array) or as a separator-separated String.

Your program may output in any way except writing the output to a variable. Writing to file, screen, modal window, command line etc. is allowed. Outputting using function return is allowed as well.

---

Test Cases

Input               Output

5*x^2               [5*x^2, 5, 1, 5*x, x, x^2]
10*x^2              [10*x^2, 10, 5, 2, 1, 10*x, 5*x, 2*x, x, 5*x^2, 2*x^2, x^2]
10*(x-y)^2          [10*(x-y)^2, 10, 2, 5, 1, 10*(x-y), 5*(x-y), 2*(x-y), (x-y), (x-y)^2, 2*(x-y)^2, 5*(x-y)^2]
x^2 - y^2           [x^2 - y^2, x+y, x-y, 1]

---

Winning Criterion

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

---

Sandbox

1. Should I allow negative constants and coefficients? Answer : No
2. Should I allow variable exponents?
3. Is there any mistake in Examples and Test Cases?
4. How long should I let this challenge be here?
5. Any problem with the Input/Output Rules?
6. Should I allow built-in to accomplish the task?
7. Any other suggestion?

Answer 12

Rotational Anagrams

Given, for lack of a better word, an anagram cube c with n rings and a word w, output whether or not you can rotate the individual sections to make w appear across the middle.

Constraints

• The letters that can appear are all printable ASCII characters EXCEPT for newlines.
  • All three characters that make up the rings can appear (|-+).
• Your program should work for cubes of any size, though the maximum I expect you to test is my biggest case (this means that if your code won't finish for n=22 on TIO, I don't care).
• Your only input should be the ASCII-art c and the word w.
• Your only output is one of two distinct values for true/false, which are arbitrary.
• You can assume the input is well-formed, and output anything for bad input.

Examples

Example cube with n=3 and w='AXMOZC':

+----A----+
| +--Y--+ |
| | +N+ | |
B X M O Z D
| | +P+ | |
| +--W--+ |
+----C----+

Rotate the outer wheel once coutner clockwise:

+----D----+
| +--Y--+ |
| | +N+ | |
A X M O Z C
| | +P+ | |
| +--W--+ |
+----B----+

Ding-ding! A match, so we can output truthy for this, but for AXMOYC there is no rotation that allows that combination, so it would return falsy. (X and Y are not adjacent on the ring, which means they can't appear at the same time.

---

Here's a small cube of n=2:

+--G--+
| +P+ |
P C P G
| +C+ |
+--P--+

For an input w=PPCG|GPCP|PCPG|GCPP this returns true, everything else is false. So you can start to see that the possible keyspace of answers is always n**2, so... hint hint.

---

Here's the big honkin' example that took me a minute to piece up.

+----------1----------+
| +--------O--------+ |
| | +------5------+ | |
| | | +----E----+ | | |
| | | | +-----+ | | | |
| | | | | +G+ | | | | |
C 3 D E - B O L L I 4 G
| | | | | +O+ | | | | |
| | | | +--W--+ | | | |
| | | +----F----+ | | |
| | +------6------+ | |
| +--------N--------+ |
+----------2----------+

And, amongst many other strings, for w=CODE-GOLFING|CODE-BOWLING you should return true.

---

This is ascii-artpermutationscode-golfparsing, if you're on my front lawn the third Tuesday of next month in a batman costume doing unspeakable things to my sprinkler system, you've won.

Answer 13

Home on the Range code-golf number

Challenge

Given a range [0,n) that has been shuffled, return the index of each element of the range.

Examples

[1, 2, 0] -> [2, 0, 1]

This is the range [0, 3) after being shuffled. The element at index 0 in the result is 2 because, in the input, 0 is at index 2. Likewise, the 0 in the output is the index of the 1 in the input, and the 1 is the index of 2.

[1, 0, 2] -> [1, 0, 2]
[0, 1, 2, 3] -> [0, 1, 2, 3]
[0, 2, 1, 3] -> [0, 2, 1, 3]
[2, 0, 1, 3] -> [1, 2, 0, 3]
[3, 2, 0, 1] -> [2, 3, 1, 0]
[4, 3, 2, 0, 1] -> [3, 4, 2, 1, 0]
[1, 2, 4, 0, 3] -> [3, 0, 1, 4, 2]
[2, 4, 0, 3, 1] -> [2, 4, 0, 3, 1]

Bonus

I will award a +100 bounty to the first person to design and explain an algorithm that solves this problem using O(n) time and O(1) space.

Sandbox

• I think my explanation was rather poor. How can I make this more clear?
• Is this a dupe?
• Is the bonus a good idea? (I really want to hear the answer because I don't know if this is even possible!)

Answer 14

Find the maximum number of coprimes in a set

Inspired by a recent question on Math.stackexchange.com, which I can't find anymore.

The challenge

Exactly what it says on the tin. You are given a set of integers and you have to create a program (according to the default definitions on meta) that outputs the size of the biggest subset that shares no divisors except for 1.

Input

A set of nonzero positive integers of length >= 2. You can take this input as per the defaults in meta.

Output

Output, print or return the size of the subset of the input that does not share any divisors except for one.

Testcases

1 2 3 4 5 6 7 8 9 10 11 12 13 14
7

1 3
1

2 3 5 7 9
4

2 3 5 7 11 13
6

Answer 15

Golf a program whose behavior is independent from Peano arithmetic

Your task is to write a program that doesn't take any input, and whose termination cannot be proved or disproved inside Peano arithmetic. This is code-golf, so the shortest byte count wins!

Rules

• Standard loopholes apply
• Shortest by count wins
• You can assume that your program runs in a machine with an unlimited amount of memory.

Tags

code-golf busy-beaver

---

Questions for meta

• Is this a good challenge?
• Is it a duplicate?
• I think the same question with a behavior independent of ZF set theory might be interesting as well (see this link for instance), but will attract very different answers; should I post it as a separate challenge?
• What can be improved? Are the tags ok?

Answer 16

Iterate over all sets

(This question needs fixing so that the output size is not too large)

Consider all possible pairs of sets of integers (can have positive, negative and zero values) A and B such that |A| = |B| = 7. Define the set T_{A,B} = {a * b | a in A, B in B}.

The challenge is to iterate over all pairs of sets A and B so that |T_{A,B}| < 19 and the largest absolute value of an integer in A or B is at most 128. As an example of one such pair of sets, A = B = {2^i | for i in {1,...,7}}.

What should my code output?

Your code should output the pairs of sets A, B along with |T_{A,B}|.

For example:

A = {2,4,8,16,32,64,128}, B = {2,4,8,16,32,64,128}, |T_{A,B}| = 13.

Running time

I don't care how long your code takes to run except you must run your answer to completion before posting an answer.

Answer 17

Code golf the Fast growing hierarchy (fgh)

if your not familiar with the fgh you migth want to check out this explantion: Large Numbers, Part 3: Functions and Ordinals

and these value aproximations: Fast growing hierarchy Approximations

the goal this code golf is to golf the following functions:

• the exact value of f_ω(x) this means you can't golf the ackermann function

• the growth rate of f_ω2(x)

• the growth rate of f_ω²(x)

In any language of your chose.

This is a code golf so the smallest program that defines each of these functions wins (Note:the functions are allowed to call each other).

It is also allowed to ask for an input x and output the 3 function values in any order.

Tags

busy-beaver,growth-rate-golf,code-golf,recursion

Sandbox notes

I'm not sure on which functions should be the target but these functions seem challenging yet golf-able in less than 150 bytes.

Upon closer inspection I realized that f_ω²(x) is probably to easy since it can be golfed with something like:

f(x,a...) {
    for i in range(a.length) {
        if(a[i] != 0) { //first non zero
            Arrays.fill(a, 0, i, x); //replace 0's with x
            a[i]--; //decrement a[i]
            return f^x(x,a);
        }
    }
    //all zeros
    return x+1;
}

f(x,n) > f_n(x)

f(x,0,n) > f_ωn(x)

f(x,0,0,n) > f_ω^n(x)

so f(x,0,...,0,x) (x zeros) ~= f_ε0(x)

Any other tags? Suggestions? Does this interest you?

Answer 18

Just One More Time code-golf

Challenge

Write a program or function that will run without error once, but will crash when run for the second time.

If you are writing a function, you may assume the function will be run twice within the same interpreter session or program.

If you are writing a program, you may assume the machine will not be rebooted between runs.

Scoring

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

Answer 19

What Tiles did I have?

Everyone should be aware of the scoring system in a classic board game: Scrabble. I remember going back into my old scrabble box and finding some old post-it notes containing old scores. I always wonder what the heck was played for some of the more insane point scores. That gave me the idea for this challenge...

---

English-language editions of Scrabble contain 100 letter tiles, in the following distribution:

• 0 points: * x 2 (These are the blank tiles)
• 1 point: E ×12, A ×9, I ×9, O ×8, N ×6, R ×6, T ×6, L ×4, S ×4, U ×4
• 2 points: D ×4, G ×3
• 3 points: B ×2, C ×2, M ×2, P ×2
• 4 points: F ×2, H ×2, V ×2, W ×2, Y ×2
• 5 points: K ×1
• 8 points: J ×1, X ×1
• 10 points: Q ×1, Z ×1

---

Your challenge is, given a single integer input between 0 and 185, output a corresponding sequence of scrabble tiles that sum to that score with a length between 2 and 100 characters in length.

The Specifics

• The letters don't have to spell anything, they just have to sum to that score.
• You can only use a tile the number of times it exists (E.G. E can be used 12 times).
• The shortest word is 2 characters long, for an input of 0 you get **.
• Outputs will not match between answers, as there are many solutions.

Inputs and Outputs

• Input should be a single integer, anything else is wrong.
• Output should be a single string, with no spaces, order of letters is arbitrary.

Example (Potential Solution)

0   | **
1   | *E
2   | EE
[... Pattern Omitted ...]
12  | EEEEEEEEEEE
13  | EEEEEEEEEEEA
[... Pattern Omitted ...]
68  | EEEEEEEEEEEEAAAAAAAAAIIIIIIIIIOOOOOOOONNNNNNRRRRRRRTTTTTTLLLLSSSSUUUU
[... Arbitrary Ordering Omitted ...]
185 | EEEEEEEEEEEEAAAAAAAAAIIIIIIIIIOOOOOOOONNNNNNRRRRRRRTTTTTTLLLLSSSSUUUUDDDDGGGBBCCMMPPFFHHVVWWYYKJXZQ

---

This is code-golf,strings: Whomever contacts Cthulhu using the dark arts first wins.

Answer 20

Display the Undisplayable

I have sometimes seen answers to challenges, written in binary machine code. The users who post them usually display them in hexadecimal representation. This representation makes the code extremely long, and does not do them justice!

Thus, we should give them help, and I don't care if they don't need it. Your task will to write a program/function/eldritch incantation to turn their beautifully golfed binary code into the shortest possible string of printable characters.

Input

A sequence of random binary data of random length. Use any of the standard IO methods (note to self: find the link to the Meta post).

Output

A sequence of printable characters. Use any of the standard IO methods.

• If encoding is relevant, you are free to choose any encoding, provided you clearly indicate which one you used in your answer. What is relevant is the number of characters anyway.

• Whitespaces (regular space, new line, non-breaking space, form feed, etc.) are considered not printable. They can be added if you wish, but their presence or absence must not impact the decoding of the output.

Conditions

• There must exist a program, that can take any possible output of your program, and turn it back into the input (providing it is not needed, but will be smiley'd at).

• If your program is run twice, with 2 inputs of same size, the 2 resulting outputs must have the same size.

• Standard loopholes apply.

Score

The score is calcaulated as the number of bytes in the input, divided by the number of characters in the output. The higher the better.

If the score varies depending on the length of the input, take its average over input sizes from 1 to 1024 bytes included (I don't think we'll have answer 1 kb long here).

---

Giving an answer in a binary language (machine code, LLVM bitcode, etc.) and adding the output when run with its own binary source will be smiley'd at (but no bonus, unless it can also summon Cthulhu).

Don't forget to explain how your code works!

---

Meta

• Do you think it's a good idea? Is there already a challenge like this one?
• Is there any blatant loophole/possible imporvements?
• What tag(s) do you recommend for this challenge? (please edit the answer)

Answer 21

Every Nth Line in Source Outputs N

code-challenge source-layout

Heavily inspired by Hello, World! (Every other character)

Related to my other Sandbox post Every Nth Char in Source Outputs N; is it a dupe?

Write a program that outputs 1. When the first, third, fifth, etc. lines are removed, it outputs 2. When all lines where their (1-based) index in the source, mod N, are not 0, are removed, it should output N.

This is code-challenge. The winner is the program that works with the largest N, while working for all n < N (obviously, to run up to N, it has to be at least N lines long). If there is a tie, the winner is the shortest answer that reaches the largest N. Your program must at least work up to N=2, since I don't think any languages will struggle with simply printing 1.

Example

Examples are based off of this sample program:

test
hi
world
hello
12345
System.out.println(test);
timeout
let's dance

For the program to work for N=1, the original program should output 1.

For the program to work for N=2, the following should output 2:

hi
hello
System.out.println(test);
let's dance

For the program to work for N=3, the following should output 3:

world
System.out.println(test);

For the program to work for N=4, the following should output 4:

hello
let's dance

For the program to work for N=5, the following should output 5:

12345

etc.

The highest N this program could work for is its line length, 8.

Answer 22

Sandboxing this mostly so I don't forget about it (as I don't want to initiate this so soon after v3). Unlikely to need any serious revision, but comments are appreciated none the less.

Prisoner's Dilemma v4: The Amnesiac Gentlemen.

This is similar to v3 Petri Dilemma, except with one significant change: no one knows what round it is. The same setup, submission format, and scoring will be used. For sandbox brevity, I'm only noting the differences from v3.

Bots will receive input at the beginning of its turn in the format:

current points, enemies points, your previous moves, enemy's previous moves

The format of the move list (both yours and the enemy's) will be a string of characters, "c" for cooperation "d" for defection, in order from first round to last. However this list will contain only the first seven moves of the game as well as the most recent 7 moves (as everyone knows, you can only hold seven items in working memory). A String 14 characters or fewer would indicate a round at the beginning of the game where 14 total moves haven't yet been performed. Later rounds would be indeterminate.

Additionally, as the current round number is not being passed in, bots will be unaware of when the end of the game comes (games will still be 200 rounds). This should prevent "Ah ha, last round, I backstab!" "Ah ha, but I backstab you first, one round earlier!" strategies, which is what dominated a large swath of the v3 strategic playspace (I did tests where all backstab-early bots were coded to all backstab on the same round and there were only two that performed sub-optimally as a result, both of which were set to backstab "before all n-Tit-for-Tat strategies", moving them back 1 rounds re-elevated them above n-Tit-for-Tat again, as well as which one backstabbed the other first determining the winner between them). While several bots from v3 would be valid submissions in v4, all of the winning bots utilize more data than v4 will let them have, opening up the playing field for new techniques.

Here are four sample strategies that will be entered to start with:

Tit for Tat

def titfortatfunc(mypoints, enpoints, mylist, enlist):
    if not enlist or enlist[counter-1] == "c":
        return "c"
    else:
        return "d"

RandomPick

from random import choice
def randompickfunc(mypoints, enpoints, mylist, enlist):
    return choice(["d", "c"])

Cooperator

def cooperatorfunc(mypoints, enpoints, mylist, enlist):
    return "c"

Defector

def defectorfunc(mypoints, enpoints, mylist, enlist):
    return "d"

Answer 23

(Code Golf) How Many Notes Are There?

Background

Most music games (MUG) describes the "instructions" that the player must follow as "notes". When the charts (set of notes) are first available, MUG players usually record the chart as a video and upload them to video sites. However, unless playing a full combo (able to pick up all notes) that the combo count directly shows the number of notes, it is usually not practical to count the number of notes one by one directly (since there are usually hundreds of notes), so they calculate that from the scores that may show on those videos if the score formula is known.

One of those examples is jubeat, which is somehow like a MUG version of "Whack-a-Mole". Although officially "instructions" are called "chips", players have the consensus to call them "notes". (For those who don't know what jubeat is please check it out here: jubeat - RemyWiki)

Objective

What you have to do, is to:

• Write a program or function,
• Which accepts a list of integers as the only input,
• That calculates the numbers of notes which is possible for all the given "basic scores".

Requirements

• The input can be an array of integers or a string containing those integers (Please indicate the input format).
• The integers in the input are guaranteed to be in the range of [0, 900000] inclusive.
• A case (NOTES in the formula) is possible means that, for each integer in the input, there exists a variable ACH, when substituted into the formula below, the formula evaluates to that integer. (See The Formula and Test Cases for details)
• All possible cases within the range [1, 1100] inclusive must be included in the output.
• The output can be an array of integers or a string containing the results (Please indicate the output format).
• If there is no case fulfilling the requirements, the program or function should either return an empty array, an empty string, null, or any objects indicating absence of results.
• NO RUNTIME EXCEPTIONS shall be thrown in any circumstances.

The Formula

The max score is 1000000, but here we only consider BASIC_SCORE, whose maximum is 900000.

The BASIC_SCORE is calculated by BASIC_SCORE = floor(floor(ACH * 100000 / NOTES) * 0.9), where ACH is an integer in the range [0, NOTES*10] inclusive except NOTES*10-1 and NOTES*10-2.

As a concrete example, take ACH=6850, NOTES=900, we have BASIC_SCORE = floor(floor(6850 * 100000 / 900) * 0.9) = 684999.

As a result, NOTES=900 is a possible case for the basic score 684999.

Test cases

 Input                                    | Output
-----------------------------------------------------------------------------------------
 896757, 846353, 844486                   | 916
 891000, 893999                           | (all multiples of 30 within [1, 1100])
 899736                                   | 1024, 1025, 1026, 1027
                                          | (342, 683, 684 are false positives because  
                                          |  in these cases ACH = NOTES*10-1 or 
                                          |  ACH = NOTES*10-2)
 873540, 802468                           | (none: no case fits all inputs.
                                          |  some cases do fit some inputs but not all)
 0, 900000                                | (all values within [1..1100])
 800000                                   | (none)

Rules and Winning Criteria

This is a code-golf, so the source code with the shortest length (in terms of bytes) wins. Standard loopholes apply.

Answer 24

Poor Man's Ransomware

This challenge is loosely inspired by the cheapo-enigma machine question. However, I beleive that the differences are substantial enough that this would not be a dupe. Feedback welcome.

---

You have been captured by a morally questionable "employer" and forced to write a piece of "ransomware". All it has to do is take in a string "in whatever format" and output another string (which can be used to recover the files) Essentially, across the set of all possible inputs (infinite) you will define a one to one function.

Participants will then publish their code to stack-exchange, where other aspiring "hackers" will try to break your code. A "cop" submission will consist of a byte count a sample plaintext and a sample "encrypted" file as well as an encrypted copy of your code.

Robbers will work tirelessly in another thread to reproduce your code. Any submission which correctly produces the corresponding "encrypted" files when fed the sample plaintext and itself will be considered to be cracked.

If your code lasts 7 days or longer you may mark your submission as "safe" by publishing the source code for the encryptor and a decryptor. Until this time robbers may still work to break your code. If anyone finds that a specific decryptor fails on a certain plaintext it is invalid.

The winning cop has the shortest safe submission and the winning robber has the largest sum of the bytes of his cracked cops. Ties go to the earlier poster. Good Luck!

Answer 25

Count bytes like a Java golfer

Java is verbose, everybody knows that. Sometimes, here on PPCG, it happens that a Java answer is shorter than 60 characters, but most of the time it's longer, way longer! And the Java golfers here often post improvement suggestions in comments.

Alas, the PPCG website is based on the stack software, which invisibly cuts <code> comments according to an obscure rule, which I shall name the "Java golfer's bane", making it impossible to get an accurate byte-count by copy-pasting.

The rule in question is the following:

• in a <code> tag, insert two invisible characters
  • the first time after 60 non-whitespace consecutive characters
  • then subsequently ever 20 non-whitespace consecutive characters

Challenge

Your goal is to help us, poor Java golfers, to get the byte-count straight from when we copy/paste code from comments.

SE software rules are, I'm sure, complex, so we will simplify a bit, but not that much.

• Your input:
  • is mappable to UTF-8;
  • must support codepoints until at least U+FFFF;
  • will contain only characters with codepoints greater than or equal to U+0020;
  • must be a string or a characters array/list if those accept unicode characters, or else must be an integer (16 bits minimum) array/list. Unless I forgot anything obvious, no other input format is allowed.
• If a sequence of non-whitespace characters in the input contains more than 60 characters:
  • keep the 60 first characters, then skip the next 2 characters;
  • then until you meet a whitespace, keep the next 20 characters and skip the next 2.
  • We don't care which are the two stripped characters.
• Your output is the size of the string after being sanitized, in bytes as encoded in UTF-8! You must support very long Java answers, up to 500 characters (not bytes).
  • You don't need to map to UTF-8 since I give the rule on how to count without mapping, but in some languages it might be easier to actually map!
• The standard loopholes are naturally forbidden.
• This is codegolf, so the shortest answer in bytes wins!

You may assume the following:

• the only whitespace character you will ever get is the space (U+0020). I abuse the term whitespace by including the start of the string as well in its meaning.
• no whitespace will be at positions 62, 94, 116, (+22) ... after the previous whitespace

You may not assume the following:

• The skippable characters will exclusively be the ones SE actually uses (U+200C U+200B);
• you will get only ASCII characters;
• you will not get any diacritics.

Bonus

• if your code supports Unicode code points up to U+1FFFFF, you can remove 10% off your byte count, do not round the resut.

How to count the number of UTF-8 bytes?

If you haven't a builtin for that, Wikipedia gives us the rule, based on code points:

first code point  |  last code point  |  # bytes
U+0000            |  U+007F           |  1
U+0080            |  U+07FF           |  2
U+0800            |  U+FFFF           |  3
U+10000           |  U+1FFFFF         |  4

Wikipedia goes beyond those number, but the RFC 3629 capped this mapping to 4 bytes, so we thank it!

Test cases

Work in progress!

---

Notes for review:

• Suggested tags: code-golf, string, unicode
• Related:
  • Bytes/Character (different as there is an additional string manipulation)

Answer 26

What feedback do you have for me?

Challenge

Convert and print out a time in a 12-hour format. HH:MM AM/PM

Examples

Input:

• 'Fri Jun 30 2017 21:14:20 GMT-0700 (PDT)'
• 'Sat Jun 31 2018 08:06:20 GMT-0700 (PDT)'
• 'Fri Jul 01 2017 01:14:20 GMT-0700 (PDT)'
• 'Sat Apr 10 2020 09:06:20 GMT-0700 (PDT)'

Ouput:

• 09:14 PM
• 08:06 AM
• 01:14 AM
• 09:06 AM

Rules

• This is code-golf so the shortest solution in bytes wins
• Standard Loopholes Apply
• You may use functions as well as programs

Answer 27

Help! My code has exploded! code-challenge

Insert backstory here

Task:

Your task is to create a program, which must follow these rules:

• It must be able to be split exactly into pieces of the same length in bytes.
• Once you have separated your program into pieces, your program must print 1 if the first "piece" is removed from your code, 2 if the second "piece" is removed, etc., until the program prints n if the nth piece is removed.

For example, if your program was the following:

aabbccdd

And it could be split into 4 equal parts of length 2, then these programs must result in the following outputs:

bbccdd -> 1 (aa is removed)
aaccdd -> 2 (bb is removed)
aabbdd -> 3 (cc is removed)
aabbcc -> 4 (dd is removed)

Scoring requirements:

Your program is scored based on the number of parts that it can be split into, with each part following the rules defined above. The more parts, the higher the score.

In the event of a tie, there is a "hierarchy" of scoring methods (with the next method in the list being used when there is a tie):

• Number of parts the program can be split equally into
• Size of the full program, in bytes (shortest byte-count wins)
• Time posted (first poster wins)

Rules:

• Each byte in the program must belong to one part.
• Each part in the program must be of equal length.

Answer 28

Introduction

Ten years ago, a secret encryption key used by DVD players was published online. When the industry tried to censor it, the internet reacted by republishing it widely—creatively incorporating the key onto shirts, a flag and even in song.

If this code golf community had existed, I'm sure we would have joined in.

Challenge

Output the number 13256278887989457651018865901401704640.

Example input and output

Input:

Not applicable.

Output:

13256278887989457651018865901401704640

Answer 29

Decode Reddit's Voting System code-golf number

Background

Users with a high enough reputation on Stack Exchange can see the number of upvotes and downvotes on each question and answer. On Reddit, however, the net vote count and percentage of upvotes are displayed. Unfortunately due to rounding errors, it is impossible to determine exactly how many upvotes and downvotes occurred.

Challenge

Given a nonzero net vote count and a percentage of upvotes, return all possible pairs of the numbers of upvotes and downvotes.

Constraints

The net vote count can be any integer in the range [-2^31, 2^31).

The percentage can be a whole number in the range [0, 100], or a floating point number in the range [0, 1] with no more than two digits; you may decide which format to accept.

The percentage represents the percentage of votes which are upvotes, rounded to the nearest integer. So a value of 93% could be anywhere in the range [92.5%, 93.5%) that would result

The maximum numbers of upvotes and downvotes will not fall outside the range [-2^31, 2^31); that is, you should be safe using 32-bit signed integers.

You may not return two ranges representing all possible amounts of downvotes and upvotes; you must specify which numbers of upvotes correspond to which numbers of downvotes; hence you must return all possible pairs.

Test Cases

1, 67%  -> [(2, 1)]
1, 100% -> [(1, 0)]
1, 60%  -> [(3, 2)]
0, 50%  -> [(0, 0), (1, 1), (2, 2), ...]; cases like this will not be valid input
More involved ones to come...

Meta

Anything I can do to make this more clear or more fun?

Answer 30

Create The Correct Path

Which would be better code golf with shortest code and being able to run on at least two operating systems or code challenge and scoring by how many operating systems it can run on?

(code-golf OR code-challenge) file-system

Given an input create a program that when ran on different operating systems creates a path for each one. For example, when ran on Windows:

[ "folder1", "folder2" ] -> folder1\folder2

Input

An array of strings or any suitable alternative. The input can be empty, in which case you would just return an empty string.

Output

The correct path for the operating system the program has been ran on.