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.

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

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Answer 1

Block partite a string

code-golf

Inspiration.

Consider a list l, consisting of numbers. Define a block operation at index i on the list l to be the act of moving 3 consecutive elements starting from i in l to the end.

Example:

l, i (1-indexing) -> l (after applying block operation at index i)
[1,2,3,4,5], 1 -> [4,5,1,2,3]
[1,2,3,4,5,6,7], 3 -> [1,2,6,7,3,4,5]

Given a list consisting of only 0 and 1, your challenge is to partite it so that zeros are at the front, and ones are at the back, using only block operations. Output should be the indices in the order they are applied on the list.

Because this is impossible for the list [1,0,1,0], the list length is guaranteed to be at least 5.

Also (as a bonus, to avoid handling special cases) there is at least 5 ones and 5 zeroes.

Test cases (1-indexing)

(there are other valid outputs)

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

Use this script to generate more test cases. (only input)

Winning criteria

This is code-golf, the shortest code in bytes wins.
Don't let code-golf languages discourage you from posting your solution. Try to come up with as short as possible solution for any language.

Note

• [atomic-code-golf] variant.
• You're free to brute force, although I expect that a non-brute-force solution would be much shorter.

Answer 2

Which number nearest?

We say 2018 is near 2000, but not 2018 is near 2030, though |2030-2018|<|2000-2018|. Given some pairs of numbers (a,b) and two numbers g>0 and x, find an x+t for min((|t|^c+g)*b^d) for t as a real number making (x+t) mod a = 0, (a,b) as one of the pairs. You can decide c to be 1 or 2, and d to be 1 or -1, as long as it's constant.

Samples: (c=1, d=1)

In: {(1000, 1), (10, 100)}, g=1, x=2018
Out: 2000

In: {(1000, 1), (10, 1)}, g=1, x=2018
Out: 2020

In: {(1, 1), (10, 1)}, g=1, x=2018
Out: 2018

code-golf

Answer 3

Is there a dangling else?

Define a statement as follows (Backus-Naur form) (based on Java syntax):

statement ::= ";"
  | "if(true)" <statement>
  | "if(true)" <statement> "else " <statement>

Example valid statements:

;
if(true);else ;
if(true);else if(true);else ;

Example invalid statement that is valid Java syntax, but considered invalid for simplicity:

if(false);
if(true);else;
if(1>0);else ;
System.out.println("This is invalid");

Your task is, given a valid statement, determine if it contains a dangling else (that is, it can be parsed into more than one ways)

Test cases

Truthy test cases (contains a dangling else)

Presented in the format {input}¶ -> {parse 1}¶ -> {parse 2}

if(true)if(true);else ;
 -> if(true){if(true);}else ;
 -> if(true){if(true);else ;}

if(true)if(true);else if(true);else ;
 -> if(true){if(true);else if(true);}else ;
 -> if(true){if(true);}else{if(true);else ;}

if(true);else if(true);else if(true)if(true);else ;
 -> if(true);else if(true);else if(true){if(true);}else ;
 -> if(true);else if(true);else if(true){if(true);else ;}

Falsy test cases (uniquely parsed)

if(true)if(true)if(true);
if(true)if(true);else ;else ;
if(true);else if(true);else if(true);else ;

Answer 4

Quine of Hanoi

Objetive

Make a program that print a rearranged version of itself

Rules

• Your program will consist of newlines and 3 blocks : A, B and C where each block will have distinct and nonzero lengths, i.e. 0 < length(A) < length(B) < length(C).
• The output will be based on the order of the code blocks and newlines, it will be a new arrangement that progresses toward a solved state by one move unless it is already solved, following Tower of Hanoi rules.

For example:

CA
B

Will print

C
B
A

Additional rules

• Your program don't have to handle invalid orders, e.g. CAB
• You have to handle at least one configuration of each group (but not necessarily all of them).
• The order of the lines is irrelevant.

For example

CA
B

CAN print

B
C
A

Examples

#Group 0 - will output itself
CBA

#Group 1 - will output one of group 0
A\nCB
CB\nA

#Group 2 - will output one of group 1
A\nB\nC
A\nC\nB
B\nA\nC
B\nC\nA
C\nA\nB
C\nB\nA

#Group 3 - will output one of group 2
CA\nB
B\nCA

Winning

This is code-golf, so the one with the shortest code (A+B+C) wins

Answer 5

Most times a loop

Given a positive integer n. For an array of length n, each two element of which are different, repeatedly rearrange it using the same permutation till it's the same as original. How many times was the array rearranged at most?

Samples:

input output example permutation
1     1      [a1]
2     2      [a2 a1]
3     3      [a3 a1 a2]
4     4      [a4 a1 a2 a3]
5     6      [a3 a1 a2 a5 a4]

Answer 6

Rotational symmetry in which bases from 2 to 36

A number (here, a non-negative integer) is rotationally symmetric if it "looks" the same after being rotated 180 degrees. For example, 69 (heh.) Here's a related challenge.

We're going to consider bases from 2 to 36, using the symbols 0-9A-Z as the digits. We're going to be generous with what digits are rotationally similar. Each of the following pairs will qualify (order not relevant):

00, 11, 22, 55, 69, 88, B8, D0, DD, E3, I1, L7, S5, SS, Z2, XX, ZZ

The challenge

Given a non-negative integer n in base 10, write a program or function that produces a list of bases from 2 to 36 in which the n is rotationally symmetric.

Input and output

Any reasonable input format is allowed (the integer itself, its character representation, an array of digits, an array of digits as characters.)

Any output format that communicates the desired result in an unambiguous way is acceptable. For example, a 35 element array of truthy/falsey values. If it's easier to include base 1 (always truthy) that's fine too.

Rules

This is code-golf. Fewest bytes in each language. Usual rules apply.

Answer 7

Challenge

n=2πr

Given an input, n, print a circle with the circumference of n characters.

Rules

• The characters for the circumference of the circle can be any non-whitespace character
• Shapes don't have to be an amazing circle, kinda roundish shapes are still valid
• The circle can have a small gap, but no overlap

Examples

Input: 1
Output:
o

Input: 2
Output:
oo

Input: 3
Output:
oo
o

Input: 7
Output:
 ooo
o   o
 oo

Input: 20
Output:
  oooooo
 o      o
o        o
o        o
 o      o    
  oooooo

Answer 8

Shortest code to send an html s/mime signed message with one attachment over smtps

Simple challenge : use a valid RSA based security certificate in order to sign message according to s/mime rules and send it over smtp over TLS on port 465 (or starttls on port 25).

Rules :

• The program parameters takes an ʜᴛᴍʟ string consisting of message body ; a message subject as string ; a sender address as string ; and list of recipients address.
  They can be obtained either as function/class parameters or program arguments or read from keyboard input.
• The security certificate is read from an hardcoded file name of your choice or a hardcoded non empty string.
  It can be in the format of your choice.
• The attachment is read is read from an hardcoded file name of your choice or 2 non empty hardcoded strings (1 for filepath and the other 1 for content)
• The s/mime signing rules state that message body should be signed and other part shoudln’t be signed, this means in practice that data stating the message is in the html format and all data about attachments should be signed (subject priority, and e‑mail addresses aren’t signed).
• When I say you have free choice, just pick up the solution using the fewest bytes.

 Winner

The code which uses the fewest bytes.

Answer 9

Earth mover's distance code-golf

Dupe check: Do we already have a challenge about the Earth mover's distance? Some possibilities could be to compute it for a 1D array, a 2D array, or a circle.

Answer 10

Fewest instructions to copy bytes in memory in WebAssembly.

Implement the functionality for copying bytes in memory in WebAssembly.

Rules

• Use WebAssembly, written in wast (the text format).
• Any of the WebAssembly instructions are fine.
• In calling copy, it doesn't need to worry about overriding an existing string.
• Doesn't need to worry about the strings being too large to fit into memory, strings will be reasonable size and wont overflow over the end. For example, the total memory is 10000 bytes, so strings might be 100 bytes and only go to 5000 in the memory. (But those aren't actual hardcodable values).
• No calling JavaScript functions.
• The string "Hello World" starts of at position 0 in memory. Copy this string to random places in memory and log it, as shown in the xample below.

The winning answer is the one with the fewest WebAssembly instructions. That is, feel free to have a functions in WebAssembly, just no calling or importing JavaScript functions.

Example

To get started, here is the start of the WebAssembly module:

// example.wast
(module
  (memory (export "mem") 1)
  (data (i32.const 0) "Hello World")
  ;; instructions counting starts from here:
  (func (export "copy")
    (param i32) ;; existing start index
    (param i32) ;; size in bytes
    (param i32) ;; new index to copy to
    ...))

And here is how to load it, as well as the tests:

// example.js
WebAssembly.instantiateStreaming(fetch('example.wasm'), {}).then(mod => {
  var exports = mod.instance.exports
  var i8 = new Uint8Array(exports.mem)
  var i = 200 + rand(500)
  exports.copy(0, 11, i)
  var i2 = 1000 + rand(500)
  exports.copy(i, 11, i2)
  console.log(i, getString(i, 11))
  console.log(i2, getString(i2, 11))

  function rand(size) {
    return Math.floor(Math.random() * (size + 1))
  }

  function getString(index, size) {
    var string = ''
    for (var i = index; i < index + size; i++) {
      string += String.fromCharCode(i8[i])
    }
    return string
  }
})

Resources

Potentially useful resources:

• Memory in WebAssembly (and why it’s safer than you think)
• Example of the .data section in wast
• Example func in WebAssembly
• Example of WebAssembly iteration with block
• WebAssembly examples

Answer 11

Concatenate my strings!

As you know, we all like to save bytes around here. So, my strings are special: they come in four different flavours depending on the highest code point in the string:

• ASC (code points up to 0x7F). Like ISO but all bytes have values less than 0x80.
• ISO (code points up to 0xFF). Each byte represents a code point.
• UTF (code points up to 0x7FF). Uses UTF-8 encoding.
• UCS (code points up to 0xFFFF). Uses UCS-2 encoding.

For input you will receive two strings, each represented by a flavour identifier and a sequence of bytes representing the code points according to the flavour. You then need to output a byte sequence using the best flavour to hold the concatenation. Except where limited by standard loopholes, you don't need to use the designations ASC, ISO, UTF and UCS, so for instance if you choose to use numbers 0-3 for the flavours then the output flavour is simply the maximum of the two input flavours.

Example:

ISO 43 6F 64 65 A0 + ASC 47 6F 6C 66 = ISO 43 6F 64 65 A0 47 6F 6C 66 

This is code-golf, so the shortest program or function wins!

Answer 12

Count binomial coefficient entries

This task is very simple. For integer \$n \ge 0 \$, given the binomial coefficients of all the expansions of \$ (x+y)^m \$ for \$ 0 \le m \le n \$, count the number of occurrences of \$ n \$. This is OEIS A003016.

This is code-golf, so the shortest program or function that breaks no standard loopholes wins!

Answer 13

Smallest Match-3 Game

codegolf game

I was reading about Match Three games, games about manipulating a field of symbols to generate lines of three or more matching symbols, and was thinking a playable game would be a pretty short program, if golfed.

The reason I think that is because it has less rules than Chess, so I thought that when golfed it'd be a simpler program shorter than the Smallest chess program, which uses 487 bytes of Assembly, or less than 2 MB in any language used to answer that question.

Here's the other questions on this site, relating to Match-3 games:

• Find the best immediate move in a "match-3" game
• Determine if a move exists in a Bejeweled/match 3 game

Question:

How small can a Match-3 Game Program be?

Rules

• The symbols used can be any ones you want, just have at least 3 different symbols.

• At least a 4x4 board. Board size can be customized, if that's somehow easier.

• Board must start with a valid configuration, can stall player interaction and visibly reform the board, but player action must only be start to be allowed on a valid board.

• Any method of moving symbols is allowed. It could be sliding rows around, instead of swapping the positions of pieces, either side by side or anywhere on the board, or some other innovative way of moving pieces. But the board starts filled, and you move the symbols already there.

• Any method of selection of what to move is allowed.

• When a match happens, it's removed, and new pieces arrive, somehow. They don't have to fall from the top.

• It'd be nice if it could detect when there's no more valid moves.

• Random progression instead of deterministic would be nice as well.

Sandbox Questions

Not sure how much variability in the end result I should have. I want to have maximum customization.

I suppose I could have the score for each entry be something like:

Bytes of code - average number of bytes used to implement each optional feature.

Answer 14

An example text for scrambled-words experiment. Version 1

Introduction

This challenge is based on an old experiment that proves that we only need first two and last two letters in order to uniquely identify a word. The remaining middle-characters can be completely scrambled and yet we should not have any problems in reading the whole word. And the speed of reading even longest scrambled-words based text shouldn't be significantly longer than reading an "normal" text.

The challenge itself is to write a shortest possible code (any language) that can be used to generate test texts to prove above described idea.

The experiment in the background of this challenge was conducted many years ago by some English or American scientist. I can't credit particular source or recall any other details. The challenge itself is created by me.

Challenge

Write the shortest possible code to generate test text (any length) based on following algorithm:

1. For each word in input text.
   • If word is 5 characters long or less -- keep it unchanged.
   • If word is 6 characters long or longer -- keep first two and last two characters unchanged and scramble remaining ones.
2. Print generated resulting text with scrambled words.

There there no corner cases except for two assumptions:

1. Words with 5 characters and less should be kept untouched.
2. Your code must support all UTF-8 characters, not just English / non-Latin alphabet.

I assume "standard" approach here, so the winner of the challenge will be determined by the length of the code.

Example Input and Output

Input:

• This challenge is based on an old experiment.
• Print generated resulting text with scrambled words.

Output:

• This chllenage is based on an old exripmeent.
• Print gertaneed reitlusng text with scbrmaled words.

An example text for scrambled-words experiment. Version 2

Challenge

The extended version of this challenge adds only one new assumption to base / above algorithm:

1. For each word in input text.
   • If word is 4 characters long or less -- keep it unchanged.
   • If word is 5 characters long -- keep first and last character unchanged and scramble remaining three.
   • If word is 6 characters long or longer -- keep first two and last two characters unchanged and scramble remaining ones.
2. Print generated resulting text with scrambled words.

And again:

1. Words with 5 characters 4 characters and less should be kept untouched.
2. Your code must support all UTF-8 characters, not just English / non-Latin alphabet.

Example Input and Output

Input:

• This challenge is based on an old experiment.
• Print generated resulting text with scrambled words.

Output:

• This chllenage is baesd on an old exripmeent.
• Pirnt gertaneed reitlusng text with scbrmaled wrods.

Answer 15

Maximal number of programming languages in 1KiB

In this code-challenge your task is to write a program/function with a maximum of 1024 bytes, the goal is to interpret/compile as many programming languages as possible.

Rules

You're free to use any combination of inputs and outputs as you wish.

Input

Inputs will be the name¹ of the programming language and the source code.

The inputs can be

• read from a file (you may hardcode a filename if it helps)
• read from stdin
• taken as command-line arguments
• taken as function arguments
• a combination of the above

^{1: you may choose to encode them, as long as the encoding is bijective - for example numbering the languages 1 through n.}

Output

The output can be

• the resulting side-effects of interpreting the program in the specified language
• valid machine code that produces the above

What is a programming language?

For the purpose of this challenge a programming language needs to be

• Turing-complete
• publicly listed, as in having one of the following:
  • an entry on Esolangs
  • an entry on Rosettacode
  • an entry on Wikipedia
  • an interpreter/compiler hosted on Bitbucket
  • an interpreter/compiler hosted on Github
  • an interpreter/compiler hosted on Sourceforge
• released before 13. July 2018
• able to do I/O

What does my interpreter/compiler need to implement?

For each of the chosen programming languages, your program does not need to implement the full language. It suffices to implement a working subset of it as long as it stays Turing-complete.

Scoring

The answer that implements the greatest number of different programming languages wins.

---

Sandbox

Tags: code-challenge, interpreter, compiler

• Should I leave the source size restriction and use a different scoring, eg. \$\frac{\#bytes}{\#langs ^ n}\$ for some \$n \ge 1\$?
• Should I disallow using polyglotting (maybe eval could be used several times that way which would be boring)?
• How should I properly define different programming languages (should I count different versions as 1 each)?
• Additional places for entries, descriptions of programming languages?
• Missing tags or other suggestions?

Answer 16

Irrational Array indexing Starts at 3.

I came across the following brilliant comment, which suggests that subsequent sets of digit from pi should be used to Index an array, from a user named on the r/programmer humor subreddit context for the curious.

To fix the duplicate problem, instead take an extra digit whenever you are about
to duplicate a key: arr[3], arr[1], arr[4], arr[15], 
arr[9], arr[2], arr[6], arr[5], arr[35] and so on.

Exercise for the reader: write a program that outputs the nth index of this array, and describe for yourself the limitations of the program (what is the maximum value of n? what is the minimum?)

Your task (should you choose to accept it), is to implement a function (or rather pair of functions/ (pair of full programs/ one of each)) that converts to and from this cutting-edge choice.

You may either write a single function that receives two inputs one being an integer input, and two being which way to go, or you can write a pair of functions and your score will be the sum of their sizes.

Put another way, implement both f(x) and \$ f^{-1}(x) \$ according to this table. You may also instead implement f(x-1), and \$ f^{-1}(x) \$ + 1 (1 indexed arrays), but you will get some stern looks.

x f(x)
------
0 3
1 1
2 4
3 15
4 9
5 2
6 6
7 5
8 35
19 950
21 841
41 6280

This problem is essentially identical to OEIS A064809, although the table there is one indexed.

This is code-golf, so shortest code in bytes wins. As always, you may use any programming language, but standard loopholes are prohibitted. What is allowed though, is that at no penalty you may optionally take in a second or third input with the first 10,000 digits of pi. Your code must work with 0<=x<=1000. Even if you choose to receive pi as input, I'll personally encourage you to write one that doesn't require pi as input, It'll obviously be unscored, but you'll earn some imaginary internet points.

code-golf

Answer 17

The Shifty Maze

code-challenge maze grid python3

---

You are a wild mouse and you have stumbled on a maze that some human has constructed to observe your behavior. The maze is littered with blobs of peanut butter and has a cache of sunflower seeds near its center. After discovering the seeds, you decide that you want to take them all home to your personal cache. You must find your way to the seeds and exit the maze. Since there are so many seeds, it takes you many trips to get them all.

Things go well your first time. You find your way to the seeds, bring a few back, and return to the maze. To your surprise, when you return the second time, the maze looks nothing like it did before, but you quickly figure out that the entrance was simply in a different place and continue navigating as usual. The next time you return to the maze, you are once again lost, but you find a familiar pattern of peanut butter dabs and find your way to the sunflower seeds once again. Naturally, you catch onto this pattern and eventually retrieve all the sunflower seeds.

The Challenge

Your task is to make a "mouse" bot that navigates through a maze where the entrance moves to somewhere else on the edge of the maze every time you exit and enter it. You have no limits on memory, but no absolute sense of direction and a limited visual field. You can only exit the maze after finding the cache. Your goal is to get all of the seeds in as few steps as possible.

Mazes

A perfect maze is randomly generated using a randomized version of Prim's Algorithm starting from a cell near the center. The seed cache will be close to the center. 10% of the cells will be dabbed with 3-5 units of peanut butter. There will not be any peanut butter on the same cell as the seed cache. The maze used for scoring will be 30x30 cells.

Actions

Each turn, you can move forward or turn 90 degrees in either direction. If there is any peanut butter on your current cell, you may also eat one unit of it instead of moving or turning. (Partially eaten peanut butter can be used to create landmarks for navigation.)

Vision

You can see every cell in a straight line in front of you until a wall obstructs your view. You can also see one cell to your left and right, provided there is no wall between that cell and your current cell.

For each cell that you can see, you can see whether there is a wall on each of the four edges of the cell, how much peanut butter is on that cell, and whether it is the seed cache or the exit.

Example

Suppose you had this maze:

+-----+-------+-+---+
|     |  5    | |   |
| ----+-- +---+ | --+
|4    |   |@   3    |
| --+-+ --+---- | --+
|   | |    4   <|   |
| --+ | --+ | | +-+ |
|         | | |   | |
| | +-- --+-+ +-- +-+
| | |    3  | |     |
+-+-+-------+-+ ----+

@ is the seed cache. Numbers are blobs of peanut butter. < is the mouse (facing west)

The vision for the mouse would look something like this:

  +-+

  + +
  | |
  + +    
   4|
  + +
    |
+-+ + +
|.(^)3
+ +-+ +

No memory limit

You can remember as little or as much as you would like. The challenge is in figuring out where you are as quickly as possible and reduce the amount of time you spend wandering.

Test Driver

The test driver can be found here.

Coding

Your solution should be compatible with Python 3.7. You should implement a class with the following methods:

• A constructor taking no arguments
• get_action, which is called with one argument representing your vision on each step of navigation (more on that below). This should return a string representing the action to take: forward, left, right, or eat are valid values. If this returns an action that cannot be taken, an exception will be thrown and your solution will be considered invalid.
• enter_maze, which is called without arguments each time the maze is entered. No return value is expected and the function doesn't actually have to do anything. The next time get_action is called, you are guaranteed to be on the cell on the edge of the maze facing away from the entrance/exit.

The Vision Object

You will receive an object with the following attributes:

• left and right: the cells to your left and right. If there is a wall that obstructs your view, this will be '???' instead of the cell view object.
• forward: a list of all the cells in your forward vision, starting with your current cell and continuing until the last cell in your vision.

Any of these cell views may also be None, indicating the entrance/exit of the maze.

Each visible cell inside the maze will be an object with the following attributes:

• forward, left, right, back: booleans indicating whether there is a wall in the given directions, oriented the same way as the mouse.
• contents: an integer representing the amount of peanut butter (if any), None (if nothing is on the cell), or 'cache' if the cell contains the seed cache.

Scoring and Rules

• Standard loopholes apply.
  • If your bot only works on the scoring maze, it is an invalid solution. Your bot does not receive enough input to distinguish the scoring maze from another maze, so hard-coding a route will produce an invalid solution.
• Run the test driver to score your result. It uses an isolated and seeded random number generator to ensure that all entries get the same maze and sequence of entrances. The total number of turns it took to retrieve all of the seeds (this takes 100 iterations through the maze) is your score.
• Include your score, your code, and an explanation in your solution post.
• You must output a valid move each turn. Moving into a wall or attempting to eat nonexistent peanut butter will result in an error that you have no opportunity to recover from.
• You may not exit the maze until you have visited the cell containing the seed cache since the last time you entered the maze.

Answer 18

Encoding nested tuples

Tags: code-golf, number-theory, set-theory, binary-tree

Related: this

---

Working on my recent esolang μ6 I found myself a neat puzzle: Given the set of all natual numbers and the set of all nested tuples over the natural numbers, find a bijection between those two sets.

A nested tuple \$t \in T\$ is recursively defined, it is one of the two:

• an natural (\$\ n \in \mathbb{N}_0\ \$) number itself: \$\;t = n\$
• a tuple of two nested tuples (\$\ t_l,t_r \in T\ \$): \$\;t = (t_l,t_r)\$

If it helps you can think of a nested tuple as a binary tree that has only values in its leaves.

Challenge

Your task is to define two programs/functions, let's call them \$\ E\ \$ (encode) and \$\ D\ \$ (decode) which are each others inverses:

Given any natural number \$n \in \mathbb{N}_0\$ the output \$E(n)\$ is a unique element of \$\ T\$ and \$\ D(E(n)) = n\$.

Given any nested tuple \$\ t \in T\$ the output \$\ D(t)\$ is a unique element of \$\ \mathbb{N}_0\$ and \$\ E(D(t)) = t\$.

Rules

Inputs to the two programs/functions can be

• an integer or a string representation thereof for \$\ E\$
• a nested tuple/list, custom data-type¹ for \$\ D\$

Outputs can either be of the same type as the input of the inverse function/program or printed to stdout.

Example

Since you're free to implement any bijection, it's difficult to give meaningful test cases. These are just a few examples using this encoding-function and this decoding-function:

0 <-> 0
1 <-> (0,0)
3 <-> ((0,0),0)
20415 <-> ((1,0),(1,2))
55340232221111877631 <-> ((0,(1,0)),(2,1))
1000000000000000000000000 <-> 500000000000000000000000

---

^{1: For example if your language doesn't support nested tuples/lists, you don't need to count its definition towards your byte count. As an example a Haskell submission could assume data T = El Integer | Nest T T.}

Sandbox

• Anything unclear?
• Is this maybe too much to ask in a code-golf?
• I could "simplify" it by asking for two \$\ E_k \$ and \$\ D_k \$ which would for all inputs \$ k \$ map \$\ \mathbb{N_0} \leftrightarrow \mathbb{N_0}^k\ \$..

Answer 19

Most Turing-incomplete Instruction Set

Tags: code-challenge, language-design

---

This challenge expects you to define an instruction set \$I = \{ \texttt{instr}_1 \dots \texttt{instr}_n \}\$ which is provably Turing complete. The catch is that any subset \$I'\$ that is proper (ie. \$I' \neq I\$) must not be Turing complete.

Challenge

Your task is to define some environment (eg. a stack, an unbounded tape, tuples, integers, funcions etc.) over which you have complete freedom to choose, let us call this environment \$E\$.

To initialize \$E\$ you will define a way of transforming the source code \$s\$ and inputs \$in_0,\dots,in_r\$ to some \$E_{initial}\$. The same holds for the output of your programming language, you can define the output as any mapping of the end state \$E_{end}\$ to your output set.

The main task is to find an as large as possible number of instructions which define a Turing complete programming language, but removing any instruction from that set must result in a programming language that is not Turing complete.

An instruction \$\texttt{instr}_i\$ takes some non-negative number \$m\$ of arguments and modifies the environment, ie.

$$ \texttt{instr}_i : A_0 \times \cdots \times A_m \times E \to E $$

where \$A_0,\dots,A_m\$ are the sets of valid arguments, you're free to define these as you wish (eg. natural numbers, integers, Booleans, labels etc.).

Submission

Your submission will contain

• the language specification
• informal proof of validity
• an implementation of the language.

Rules

• this is a code-challenge and your score will be the number of instructions, the goal is to maximize this number (ties will be broken by favouring the earliest submission)
• your programming language only needs to support input by using some special initial environment \$E_{initial}\$
• the same holds for the output(s), these only need to be encoded in the final \$E_{end}\$
• the definitions of \$E\$ and the way of transforming input/output do not need to be formal (eg. it suffices to just say something along the lines of: "My language works with a stack of integers, initially it will contain all the inputs beginning with the first one at the bottom of the stack. Output will be the top of the stack or zero if it's empty.")
• you will need to provide an informal proof of why your submission is valid, consisting of
  • an informal proof of Turing completeness of the instruction set \$I\$
  • an informal proof of why any proper subset of \$I\$ is not Turing complete
• these proofs may rely on reductions to known Turing complete languages (eg. Turing machines, BitBitJump, brainfuck etc.)

Sandbox

As pointed out by Nathaniel, it is currently possible to get an arbitrary large score.. If anyone has a nice fix that will prevent that (and similar exploits), please leave a comment.

Answer 20

Define the structure X as a non-empty array of (smaller) X objects and "1". Split an X object into the smallest amount of continuous parts Y, length of each of Y don't exceed n, so that each X is either part of a Y, or exactly some Ys. It's fine if output only express which part has how many 1's.

Samples:

[1,[1,1,1]],3 => 1;111
[1,[1,1,1]],2 => 1;11;1 or 1;1;11
[[1,1,1],[1,1,1]],1 => 1;1;1;1;1;1
[[1,1,1],[1,1,1]],2 => 11;1;11;1 or etc.
[[1,1,1],[1,1,1]],3 => 111;111
[[1,1,1],[1,1,1]],4 => 111;111
[[1,1,1],[1,1,1]],5 => 111;111
[[1,1,1],[1,1,1]],6 => 111111

Answer 21

Game of Circles king-of-the-hill

This is a hidden-identity game with Detectives and Robbers. You will write either a Detective bot or a Robber bot. All Robbers know the identity of all other Robbers. Each turn, a bot must either:

1. Draw a private circle:
   • The actual circle drawn is public information
   • Detectives receive the number of Robbers in the circle privately
2. Draw a public circle
   • The player that draws the circle declares the number of robbers in the circle (may or may not be true)

Finally, the player with the most circles (public or private) around them dies. In the case of a tie, no player dies.

The game ends when a single side has been eliminated or when no players have died for 3 turns.

Each game consists of 17 Detective and 3 Robbers. (META: These numbers I'm not sure about).

The bots that will participate in each game will be chosen using two genetic algorithms. There will be 100 simultaneous games, and the first genetic algorithm will choose the 1700 players for the Detectives, while the second genetic algorithm will choose the 300 Robbers. The fitness function for each bot will be how long they survived in the game (by percentage).

After 1000 rounds, players are ranked by their population (two scoreboards, one for Detectives, one for Robbers)

Answer 22

4B/5B Encoding

Tags: code-golf, encode, kolmogorov-complexity, string

---

To transmit data in binary there's a technique called NRZI where a transition from +V to -V or vice-versa encodes a 1 and the absence of such a transition a 0.

In case there are a lot of 1 s this is a good method because there will be a lot of transmissions and the risk of getting out of sync is smaller, however it's still tricky for long runs of 0. One solution is 4B/5B encoding which takes 4bits and encodes it in 5bits in a way such that there are at most 3 consecutive bits. The encoding is as follows:

0000 -> 11110
0001 -> 01001
0010 -> 10100
0011 -> 10101
0100 -> 01010
0101 -> 01011
0110 -> 01110
0111 -> 01111
1000 -> 10010
1001 -> 10011
1010 -> 10110
1011 -> 10111
1100 -> 11010
1101 -> 11011
1110 -> 11100
1111 -> 11101

Challenge

Given an bytestring, you will need to encode it with the aforementioned encoding.

Rules

• Input will be a bytestring
  • to avoid padding-issues, it will always have a length that is a multiple of 4 bytes
• Output will be of the same a bytestring
• You may not assume that input (nor output) is printable

Examples

Note: You need to handle both printable and unprintable examples!

ASCII examples

ORLY -> WWEis
OBMO -> WUEm]
SSePCcGG -> ]WW-~U]U=O
aHAHaHAHaHAHaHAHaHaO -> rU%%RrU%%RrU%%RrU%%RrU'%]
S#KPOCFWcSaOCR!@sz!\q9OKqY!L -> ]iU]~WUU9ouWW%]UWJ%^}_j%zzk5uWzW:%Z

Unprintables in hexadecimal

c0 ff ee 00 -> d7 bb de 73 de
66 6f 6f 00 -> 73 9d d7 77 de
50 50 43 47 -> 5f 97 e5 55 4f
48 65 6c 6c 6f 2c 20 57 6f 72 6c 64 21 00 00 00 -> 54 9c b7 69 da 77 69 aa 79 6f 77 5f 47 69 ca a2 7d ef 7b de

Answer 23

Drat! This was actually run three years ago! See Implement INTERCAL's Binary Operators

Mingle and Select

code-golf

---

The programming language INTERCAL has two operators, "mingle" or "interleave" (represented by $), and "select" (represented by ~).

Mingle takes two 16-bit values and produces a 32-bit value by taking single bits alternately from its left and right operands, and concatenating them together - for example, 65535 $ 0 will yield -1431655766 as follows: 65535 is 0xFFFF, or 0b1111111111111111; 0 is 0b0000000000000000. Taking the bits alternately gives 0b10101010101010101010101010101010, or 0xAAAAAAAA, which evaluates to the signed integer -1431655766.

A simplified implementation of Select takes two 32-bit operands, and produces a 32-bit value by comparing the bits in the two operands, and wherever the right operand has a 1 bit, take the corresponding bit from the left operand. The resulting bits are compressed to the right, and zero-filled on the left - for example, an 8-bit version of select, given 79 ~ 42, would return 3, as follows: 79 is 0b01001111, and 42 is 0b00101010. Numbering the bits from the left starting with 1, we need to take the third, fifth, and seventh bits of 79, which are 0, 1, and 1, respectively. We then compress them to the right - 011 - and zero-fill, yielding 0b00000011, or 3.

The challenge

Without using INTERCAL, and without using in any other language any operator builtin that amounts to either mingle or select, implement both operators. You may implement them for 16- or 32-bit integers, and as either operators or functions, but input and output must be UNsigned decimal integers. (I'm not going to require input or output in INTERCAL-style insanity!)

Further constraint: The minimum bit width of the operands must be 16 bits for mingle (no constraint for select), and if they are unequal in width, the shorter is zero-filled on the left to match the width of the longer (zero fill applies to both mingle and select).

test cases to be written and inserted here

This is code-golf, so shortest solution in each language 'wins'. (Naturally, the standard loopholes are forbidden.)

Answer 24

Lucas and Fibonacci are in pair

Answer 25

Delimiter-Chaos

Write a program of at most 150 bytes length that produces different outputs (to stdout) if you insert token-delimiters into the source code.

Score

The program with the highest number of different outputs wins.

Rules

For this challenge, we assume that the source code is tokenized prior to compilation/ interpretation. A delimiter is any character which, when inserted at a given position, changes the way the source code is tokenized, but is not part of a token on its own.

Example

(python)

a = "0"
b = "0"
ainb="12"
print(ainb)

This prints 12. If you insert two spaces, you get:

a = "0"
b = "0"
ainb="12"
print(a in b)

which prints "True"

This gives a total score of 2 for 2 (known) different outputs

Rule clarifications

• Only program versions that exit with zero error code count towards the score.
• All versions have to be listed explicitly in the answer.
• Put the score into the title of the answer.
• If your code produces different outputs in different programming languages, they count.

Answer 26

Write in Ge'ez!

Ge'ez is a now-dead language used for liturgy in the Ethiopian Orthodox Church. It's traditionally written in a very distinctive script with many loops and curves. But for ease of reading, it's often transliterated into Latin letters.

Your task here is to take some writing in Latin characters and convert it to the Ge'ez script. For example, the input gəʿəz (the name of the language) should give the output ግዕዝ.

Details

Every letter in the Ge'ez script represents both a consonant and the following vowel. There are eight vowels

ä u i a e ə o wa

and twenty-six consonants

h l ḥ m ś r s ḳ b t ḫ n ʾ k w ʿ z y d g ṭ p̣ ṣ ḍ f p

which give 208 combinations. (In reality, some of these combinations like "wwa" don't actually happen, and there are some extra letters like "mya" not covered by this system, but ignore all that for the purposes of the challenge.)

The combinations are encoded in a convenient way in Unicode. The consonant defines the starting position, and the vowel defines the offset.

C    start (hex)
----------------
h    1200
l    1208
ḥ    1210
m    1218
ś    1220
r    1228
s    1230
q    1240
b    1260
t    1270
x    1280
n    1290
ʾ    12A0
k    12A8
w    12C8
ʿ    12D0
z    12D8
y    12E8
d    12F0
g    1308
ṭ    1320
p̣    1330
ṣ    1338
ḍ    1340
f    1348
p    1350

V    offset
-----------
ä    +0
u    +1
i    +2
a    +3
e    +4
ə    +5
o    +6
wa   +7

(Again, reality is a bit more complicated, but ignore that for the challenge.)

Your task is to take a string written in Latin letters, and output the corresponding Ge'ez syllables. If a consonant is followed by a vowel, add the consonant's start point to the vowel's offset, and print the corresponding Unicode character. If a consonant is not followed by a vowel, use the start point with no offset (as if the vowel were ä).

Input is a Unicode string, or a list of Unicode codepoints as integers. Output is a Unicode string, or a list of Unicode codepoints as integers. A "Unicode string" here can be in any official encoding (UTF-7, UTF-8, UTF-16, UTF-32…). NFC and NFD are both acceptable.

This is code golf; shortest code (in bytes) in each language wins. Standard loopholes forbidden.

Test cases:

gəʿəz    ግዕዝ
[TODO more to come here]

Answer 27

Cleanup after Easter

king-of-the-hilljavascript

As most people (probably) know, Easter was about a month ago. But around the community park, there're still some eggs hidden! Can you build a (Javascript only, please) bot to help us find them?

The Course:

The bots will compete on a 201 by 201 field, with coordinates ranging from (-100,-100) to (100,100). All bots will start at (0,0) and will begin. The course has 3 types of areas: wall, egg, and grass.

Finding Eggs:

You will build a function to find the Easter eggs. To see, use the function checkZone(x,y). The ouputs are:

0=Grass
1=Wall
2=Egg
3=Bot

To find a player, use findPlayer(name) (Returns coordinates array) or detectPlayers(x,y) (Returns name or null). If your bot lands on a spot with an egg, it will not be able to pick it up until it uses the function fetchEgg(). If there is not an egg, your turn will stop.

Moving:

Moving is done by returning a string. This string can be north, south, east, west, or none. Assume that directions are like a compass placed on a Cartesian plane:

North=Y+1
East=X+1
South=Y-1
West=X-1

Winning:

When all eggs are found, the game is over. If you move North to an egg, you must pick it up on the next turn in order to obtain it. If you try to move into a wall, nothing will happen. To get your current position, use getLocation(), which returns an array [x,y]. Use getBasket() to get how many eggs you have. The course will be designed so that all eggs are accessible, but some may be hard to get. If an egg is found by two bots in the same turn, each bot get 0.5 added to their basket, as they split the reward.

Functions list:

checkZone(x,y): Returns an integer, takes 2 integers as parameters between -100 and 100
    0=Empty
    1=Wall
    2=Egg
findPlayer(name): Takes string as parameter, returns player's position as an array of integers or null if player is nonexistant
detectPlayers(x,y):  Returns an array of player names, takes 2 integers as parameters between -100 and 100
fetchEgg(): Fetches egg in current position if exists
getLocation(): Returns array with x and y coordinates
getBasket(): Returns number of eggs in basket
move functions: Returns true or ends turn (Ends turn if cannot move)

Example:

function rabbitInDisguise() {
    var loc = getLocation();
    if (getLocation(loc[0], loc[1]) == 2) {
        fetchEgg();
    } else {
        if (getLocation(loc[0], loc[1] + 1)) {
            moveNorth();
        } else {
            moveEast();
        }
    }
}

UPDATE 1: Added findPlayer(name) and detectPlayers(x,y) functions, made locating functions "background", and added simultaneous egg finding rules

UPDATE 2: Added functions list

Answer 28

Compute strings with a fixed distance

Consider a binary string of total length N. For example 000111000111 with \$N=12\$. We can store this string more efficiently by just recording the indices where bits are first flipped. In this case \$(3, 6, 9)\$ is sufficient information to reproduce the string. Here are some more examples using this representation:

10101010 is represented inefficiently by (0, 1, 2, 3, 4, 5, 6, 7)
1111100000 is represented by (0, 5)
0000011111 is represented by (5)

Let us call this representation of a string its compressed representation (even though sometimes the compression is worse than doing nothing).

Now recall the Levenshtein distance between two strings. This is the minimum number of single character insertions, deletions and substitutions needed to transform one string into the other.

Task

Given a compressed representation of a string \$S\$ of uncompressed length \$N\$ and two positive integers \$k\$ and \$d\$, the task is to output the compressed representation of \$k\$ distinct strings of uncompressed length \$N\$, each with Levenshtein distance exactly \$d\$ from \$S\$. If there are not that many distinct strings possible, simply output as many as possible.

Your code must run with \$N = 1000000\$ and \$k, d < 20\$ in less than a minute on a normal desktop PC.

code-golf

Answer 29

Find the fixed point prime

number-theoryfastest-algorithmrecursion

---

Definition

Let f(n) be the sum of the sums of each possible factor permutation of n. Determine (Y f)(n) (a fixed-point combinator) for all n from 2 to the input i (where i is an integer greater than 2).

Example

A quick example of f(n) first:

f(8) = (2 + 2 + 2) + (2 + 4) + (4 + 2) + (8)
f(8) = 26

An example of (Y f)(n):

(Y f)(8)
  f(8) = 26 (shown above)
  f(26) = (2 + 13) + (26) = 41
  f(41) = (41) = 41
(Y f)(8) = 41

Let g(i) define a function which implements the described problem.

g(2)
2

g(4)
2
3
41

g(8)
2
3
41
5
11
7
41

Competition

This is a fastest-algorithm challenge, which means that the solution with the lowest asymptotic time complexity (in Θ(...)) wins!

In the case of a tie, the winner will be determined by fastest-code rules, so please submit an implementation of your code along with the algorithm. Tie-break will occur on a Google Compute Engine n1-standard-8 instance.

Answer 30

Bijective base banana to decimal

I'm trying to decide between 2 versions of this challenge:

---

Prefixes version

Let bijective base banana be bijective base 6 with each digit represented by a different prefix of the word "banana" as follows:

1: "b"
2: "ba"
3: "ban"
4: "bana"
5: "banan"
6: "banana"

The input will be a string made up of a concatenation of zero or more of only these strings. This represents a number in bijective base 6 (with most significant digit first).

The output will be the same number in (non-bijective) decimal.

For example: (input : output)

"" : 0
"b" : 1
"bb" : 7
"bbanana" : 12
"bananab" : 37
"bananabanana" : 42

A worked example:

bananabanbana
banana ban bana
6      3   4
6*36 + 3*6 + 4*1
216  + 18  + 4
238

This is code golf, so the winner for each language is the code with the fewest bytes.

---

Suffixes version

Let bijective base banana be bijective base 6 with each digit represented by a different suffix of the word "banana" as follows:

1: "a"
2: "na"
3: "ana"
4: "nana"
5: "anana"
6: "banana"

The input will be a string made up of a concatenation of zero or more of only these strings. This represents a number in bijective base 6 (with most significant digit first).

The output will be the same number in (non-bijective) decimal.

For example: (input : output)

"" : 0
"a" : 1
"aa" : 7
"abanana" : 12
"bananaa" : 37
"bananabanana" : 42

A worked example:

bananaananana
banana ana nana
6      3   4
6*36 + 3*6 + 4*1
216  + 18  + 4
238

This is code golf, so the winner for each language is the code with the fewest bytes.

---

Sandbox questions

• Is this a duplicate or near enough a duplicate to be worth changing?
• Are there any flaws that would make the challenge uninteresting?
• I'm considering changing from prefixes to suffixes following this comment from H.PWiz
• I currently prefer the suffixes version, but the worked example shows that the interpretation is no longer unique. It would either need to be specified that the match must be greedy (or non-greedy) or a different word would need to be chosen. I lean towards choosing a word which still gives enough ambiguity to force looking ahead, while still keeping the overall conclusion unique. I can't see a way of doing this without making the last character unique though, which reduces to a reversed version of the prefixes version (you can still ignore all other letters).