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

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  • \$\begingroup\$ How are tags added to questions? \$\endgroup\$ – guest271314 Jan 9 at 7:51
  • \$\begingroup\$ @guest271314 You can use this markup to create a tag in a draft: [tag:code-golf] \$\endgroup\$ – DJMcMayhem Aug 29 at 15:19
  • \$\begingroup\$ Why no featured anymore? Can't we have it auto-added or something? \$\endgroup\$ – JL2210 Sep 26 at 15:57
  • 1
    \$\begingroup\$ @JL2210 We now have a permanent info box that links to the Sandbox, so the featured tag isn't necessary \$\endgroup\$ – caird coinheringaahing Sep 29 at 13:43

2617 Answers 2617


Too many spies

You are fighting an extensive network of enemy spies. You know that each spy has at least one (sometimes multiple) fake identities they like to use. You'd really like to know how many spies you're actually dealing with.

Luckily, your counter-intelligence agents are doing their job and can sometimes figure out when two fake identities are actually controlled by the same enemy spy.

That is to say:

  • Your agents don't always know when two fake identies have the same spy behind them, however
  • If an agent tells you two fake identities are controlled by the same spy, you trust they are right.

Agent messages

Agents send you cryptic messages telling you which identities have the same spy behind them. An example:

You have 2 agents and 5 fake identities to deal with.

The first agent sends you a message:

Red Red Blue Orange Orange

This means they think there are 3 spies:

  • the first one (Red) controlls identities 1 and 2
  • the second one (Blue) controlls identity 3
  • the third one (Orange) controlls identities 4 and 5

The second agent sends you a message:

cat dog dog bird fly

This means they think there are 4 spies:

  • the first one (cat) controlls identitiy 1
  • the second one (dog) controlls identities 2 and 3
  • the third one (bird) controlls identity 4
  • the fourth one (fly) controlls identity 5

Compiling the intel we see:

Identities:   id1    id2    id3    id4    id5 
Agent 1:    |--same-spy--|       |--same-spy--|
Agent 2:           |--same-spy--|
Conclusion: |-----same-spy------||--same-spy--|

This means there are at most 2 spies.


Identities owned by the same spy do not have to be consecutive, i.e. a message like:

dog cat dog

is valid.

Also, the same word might be used by two different agents - that does not mean anything, it's just a coincidence, e.g.:

Agent 1: Steam Water Ice
Agent 2: Ice Ice Baby

Ice is used by both agents - the Ice used by the first agent is unrelated to the two occurences of Ice used by the second agent.


Compile all your agents' intel and figure out how many enemy spies there really are. (To be more precise, get the lowest upper bound, given the limited information you have.)

The shortest code in bytes wins.

Input and Output spec

The input is a list of n lines, which represent n messages from agents. Each line consists of k space-separated tokens, same k for all lines. Tokens are alphanumeric, arbitrary length. Case matters.

The output should be a single number, representing the number of distinct spies, based on your agents' intel.


Example 1


Angel Devil Angel Joker Thief Thief
Ra Ra Ras Pu Ti N
say sea c c see cee



Example 2


Blossom Bubbles Buttercup
Ed Edd Eddy



Example 3


Botswana Botswana Botswana
Left Middle Right



Example 4


Black White
White Black


  • 1
    \$\begingroup\$ The core problem of union set is nicely presented, but the input requirements are rather too restrictive. The question will be better received if the input is permitted to be received as an array of arrays or any other reasonable list format. See codegolf.meta.stackexchange.com/q/7853/194 \$\endgroup\$ – Peter Taylor Jul 16 at 8:22

Originally posted on main site, moved here for more suggestions. Better scoring mechanics required.


I've been browsing all those challenges and was thinking "yeah, they're good, but what if we make GoL one?", so here it goes.


Build starting setting for either Conway's Game of Life or other similar cellular automaton (restricted to ones with binary cell state) which after known amount of generation will include square area containing representation of QR code decodable to string "Hello, world!".

  • Cell (non-empty state) is interpreted as black pixel, no cell as white.
  • Your automation should take at least one generation until result (no hardcoded results allowed).
  • Your automation operates on infinite board.
  • Not sure if this option will be useful, but you can specify scaling ratio: single integer, setting side of square encoding single pixel. Pixel's color is color of cell dominating by count in it (you can specify 50/50 edge case resolution in your answer). Obviously, in this case side of output area should be proportional to scaling ratio. This option doesn't affect scoring.
  • It's not necessary, but nice to provide either link to online demo or .rle file.

Example result

enter image description here

Decodes to "Hello, world!"


Your score is calculated as

score = (initial amount of cells)^2*(number of generations until result) + (number of cells out of output area)*5

Lower score is better.

Happy GoLfing!

  • 1
    \$\begingroup\$ I think this challenge is interesting, although I suggest that the scoring criterion be a combination of the number of initially on cells and the number of generations necessary to get to the final output, without counting the number of on cells in the output (otherwise there's an aspect of QR code golf in the challenge as well, which complicates matters more). Also, I don't really understand the 4th bullet point. Finally, you seem to want to allow different binary cellular automata to compete, just like different languages. Is this true? \$\endgroup\$ – Erik the Outgolfer Jul 14 at 22:48
  • \$\begingroup\$ @EriktheOutgolfer Why would including amount of cells out of output area be bad? It only counts cells which aren't part of QR code, so it seems acceptable. 4th point may probably need some illustrations to make it easier to get (or just remove that). You got the last part right. \$\endgroup\$ – val says Reinstate Monica Jul 14 at 23:34
  • \$\begingroup\$ Oh, I misread the "out of output" part. So you allow extraneous on cells outside of the QR code with a penalty? \$\endgroup\$ – Erik the Outgolfer Jul 14 at 23:36
  • \$\begingroup\$ @EriktheOutgolfer I think that is more or less fine to have some cells on field as long as output in specified area is correct by itself. \$\endgroup\$ – val says Reinstate Monica Jul 14 at 23:37
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    \$\begingroup\$ Could you clarify what classes of automata are eligible? You've specified only binary (two possible cell states). What neighbourhoods are valid? Only the standard 3 by 3 Moore neighbourhood, or also other size and shape neighbourhoods like Von Neumann neighbourhoods? Must all cells in the neighbourhood contribute equally to the outcome (a totalistic automaton) or can different patterns of the same number of "on" cells give different results? \$\endgroup\$ – trichoplax Jul 16 at 21:06
  • 1
    \$\begingroup\$ Where you choose to draw the line is entirely up to you, but it could have a large effect on the nature of the challenge. For example, if arbitrary size and shape neighbourhoods are allowed, with rulesets based on the arrangement of "on" cells rather than just how many are "on", it may be possible to choose a ruleset that gives the output in a single step (maybe - I haven't thought it through). Whether you see that as a bad thing or an interesting way of solving the challenge will determine how restrictive you choose to be. Personally I'd stop short of allowing quite that much flexibility... \$\endgroup\$ – trichoplax Jul 16 at 21:09
  • \$\begingroup\$ Is there a standard for QR that avoids all disagreement as to what's a valid code? On further thought, it might be better just to requre a fixed output pattern, like some pixel version of Heelo World, and not have the whole QR layer. \$\endgroup\$ – xnor Jul 16 at 21:35
  • \$\begingroup\$ In particular, following @xnor's comment, does "decodable to" mean that errors are allowed as long as they're below the threshold for correction? \$\endgroup\$ – Peter Taylor Jul 17 at 10:55

How long's left?

Posted here.

  • \$\begingroup\$ Shouldn't the third test case be FifTy Nine MiNutes And ForTy Six SeConds? \$\endgroup\$ – Erik the Outgolfer Jul 9 at 19:26
  • \$\begingroup\$ @EriktheOutgolfer Thanks, fixed \$\endgroup\$ – Geza Kerecsenyi Jul 9 at 19:27
  • \$\begingroup\$ @Shaggy the challenge here isn't to calculate the number of syllables: it's to find the first number that has the same number of syllables as the distance from the current time. \$\endgroup\$ – Geza Kerecsenyi Jul 11 at 21:14
  • \$\begingroup\$ Ah, OK, I get it now. Yeah, I think that's sufficiently different, so; ignore my previous comment! \$\endgroup\$ – Shaggy Jul 11 at 21:17
  • \$\begingroup\$ Could you please clarify how many syllable each number has? (A list should help.) \$\endgroup\$ – tsh Jul 12 at 7:38
  • \$\begingroup\$ @tsh done, see now. \$\endgroup\$ – Geza Kerecsenyi Jul 12 at 15:05

Irish Snap: Variant Rules


Recently, me and a couple of my friends decided to play some cards, and one of them suggested the game 'Irish Snap', which was the inspiration for this challenge. However, I later learnt that the game has a lot of different rules that work ,some of which are listed here. The rules that are in this challenge aren't currently listed on that page, hence the name, 'Variant Rules'

The Challenge

Given an array of 3 cards, output a truthy or falsey value depending on if they make a valid snap in a game of Irish snap.


The input will be an array of 3 numbers, ranging from 1-13 inclusive, with 11 being jack, 12 being queen and 13 being king. The last number in the array will be the number at the top of the stack of cards.


The 4 different criteria for if cards make an Irish snap are a snap:

  • The top and middle cards are the same
  • The top and middle cards have a difference of one
  • The top and bottom cards are the same
  • The top and bottom cards have a difference of one

If any of these criteria are met, you must output a truthy value. As well as this, for the two criteria that require the cards to have a difference of one, it 'wraps around', meaning that an ace and a king are considered to have a difference of one, and vice versa.

Test Cases

Input -> Output
1 13 7 -> False
1 4 13 -> True
9 3 6 -> False
8 9 7 -> True
2 6 5 -> True
12 5 11 -> True
10 4 8 -> False
12 13 7 -> False
9 7 10 -> True
7 3 1 -> False
  • 1
    \$\begingroup\$ Wikipedia describes a substantially different game under the same name. Is there any less ambiguous name for this? \$\endgroup\$ – Peter Taylor Aug 6 at 8:27
  • 1
    \$\begingroup\$ Although I don't think there is a less ambiguous name for it that I can find, the version I described is a combination of the alternate rules listed below the section you linked: 'conventional snap', 'runs', 'sandwiches' and the last rule I listed is basically a combination of 'runs' and 'sandwiches'. How could I change the name to reflect this? \$\endgroup\$ – EdgyNerd Aug 6 at 8:38
  • \$\begingroup\$ Should I change the name to "Ultimate Snap", as that's what Wikipedia says those rules are commonly referred to as? \$\endgroup\$ – EdgyNerd Aug 6 at 8:42
  • 1
    \$\begingroup\$ I think runs as described requires all three cards and in the right order. Maybe "Irish snap: variant rules" would be a suitable title, and the introduction can reference Wikipedia and say that the exact rules we'll be using aren't listed (at time of writing the question). \$\endgroup\$ – Peter Taylor Aug 6 at 8:49
  • \$\begingroup\$ Ok, I've added in all of those suggestions \$\endgroup\$ – EdgyNerd Aug 6 at 11:23
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    \$\begingroup\$ As our token Irishman, I endorse the keeping of "Irish Snap" in the challenge name! \$\endgroup\$ – Shaggy Aug 7 at 21:22
  • \$\begingroup\$ Do you think I'll be able to post this now? \$\endgroup\$ – EdgyNerd Aug 20 at 9:44

Find the Lowest Common Ancestor of Two Nodes In A Binary Tree

Any two separate nodes in a binary tree have a common ancestor, which is the root of a binary tree. The lowest common ancestor(LCA) is thus defined as the node that is furthest from the root and that is the ancestor of the two nodes.

The following are binary trees and the lowest common ancestors of the some of their nodes.

Binary Tree 1

The LCA of 13 and 15 is 14.

The LCA of 47 and 49 is 48.

The LCA of 4 and 45 is 40.

The LCA of 13 and 14 is 14.


Write the shortest program possible that accepts as input the root of a binary tree and references to any two nodes in the binary tree. The program returns a reference to the LCA node of the two inputted nodes.


The binary tree does not have nodes with parent field references in any form. You may not use parent field references in your program.


The root of a binary tree and references to any two nodes in the binary tree. This may be in the form of a reference to the root object or even a list that is a valid representation of a binary tree.


Returns a reference to the node that is the LCA of the two inputted nodes.

Definition of a Binary Tree

A tree is an object that contains a value and either two other trees or pointers to them.

The structure of the binary tree looks something like the following:

typedef struct T
   struct T *l;
   struct T *r;
   int v;

If using a list representation for a binary tree, it may look something like the following:

[root_value, left_node, right_node]
  • 2
    \$\begingroup\$ I mostly like your binary tree questions, but it would be nice if your definition was more inclusive of languages without the concept of pointers. Something like 'input will be a tree where a tree is either something containing a number and two other trees, or else something representing nothing. A tree must not be ambiguous'. This would include strings like [5[][7[6[][]][8[][]]], where a tree is [number tree tree] or [] as well as the usual standard binary tree structures and lists \$\endgroup\$ – Jo King Aug 9 at 6:45

Truth Table Composition

Given 2 or more truth tables, output the "shortest" way to compose the first N-1 tables to form the last (Nth) table.


  • Standard loopholes/io rules apply.
  • Input is a "list" of truth tables
    • A truth table is a "list" of rows that contain the inputs and the corresponding output
      • The input will always be the same length for a given table
      • There must be \$ 2^N \$ rows in a given table, where N is the number of inputs in the table
      • Each row must have distinct input
      • Inputs and outputs must both be "booleany" e.g.:
        • true/false
        • 1/0
        • truthy/falsey
        • "Bob"/"Sally"
    • The input can be in any reasonable format.
      • Any of the formats shown here are reasonable.
      • Taking the output first (ie for &: 1,1,1;0,0,1;0,1,0;0,0,0) is reasonable.
      • Input that requires non-trivial logic to convert is not reasonable.
      • When in doubt, ask in the comments.
  • Output is a "nested structure"
    • Each level of the nest contains information of the:
      • Truth table that was used
      • The ordered inputs (of this structure)
    • If a node is a leaf (one of the inputs to the final truth table) it must:
      • Be distinguishable from the other nodes
      • Contain the index of the input to the final table
    • Output format must be reasonable (see details under input)
  • "Shortest" is measured by the number of nodes in the output structure.
  • It will always be possible to construct the last table with the first N-1.
  • You do not need to handle invalid input.
  • This is , so the answer with the smallest asymptotic time complexity wins! Answers that do not aim to be efficient are also welcomed.

Yes, I'm done with rules now. Sorry.

Test Cases

For these test cases, the output is explained below. Note that this is not the output format you have to use! - $N is the Nnt input to the final table (0-indexed) - N(...) is the Nnt input table applied to ... (also 0-indexed) - Arguments are comma separated and are in this format. - Note that N() is different from $N; the former is the Nnt truth table applied to nothing (only valid in the case of truth tables 1 and 0), and the latter is the Nnt input to the final table.


1 0 0
0 1 1
0 0 0
1 1 1

$1 (length 1; leaf; gives the second input)
1 0
0 1

1 1 1
0 0 1
0 1 0
1 0 0

1 0 1
1 1 0
0 0 1
0 1 0

0($1) (length 2; the first table (not) applied to the second input)
1 0
0 1



0(1()) (length 2; the first table (not) applied to the second table (true))
0 1
1 0


1 0
0 1

0($0) (length 2; the first table (not) applied to the first input to the final table)
0 1
1 0

1 1 1
0 1 0
1 0 0
0 0 0

1 1 1
0 1 1
1 0 1
0 0 0

1 1 0
0 1 1
1 0 1
0 0 0

1(2($0,$1),0(1($0,$1))) (length 8; "(A | B) & !(A & B)")


I think more test cases are needed, but am unsure what to add.

This is my firstsecond challenge, so all feedback is welcome!

  • \$\begingroup\$ The idea is good, I think. I had trouble understanding at first read though, and didn't understand at all your $ things. I suppose $1 is the same as 1() but I'm not sure. Suggested test case: Input : (1,0;0,1) ; (1) ; (1,0;0,1) with Output : 0() and not 0(1()) or 1(0()). \$\endgroup\$ – V. Courtois Aug 13 at 14:40
  • \$\begingroup\$ @V.Courtois $0 is the first input to the final table, $1, the second etc. 0(...) is the first input table, 1(...) is the second, etc. Any recommendations on a better format? \$\endgroup\$ – tjjfvi Aug 13 at 14:43
  • \$\begingroup\$ @V.Courtois Added your test case, though 0() is not a valid output as (1,0;0,1) takes in 1 input, not zero, it should be 0($0) \$\endgroup\$ – tjjfvi Aug 13 at 14:46
  • \$\begingroup\$ Do you mean $0 is the input on the first row of the output table? It got even more foggy... Plus, isn't a truth table's order meaningless? I mean, you even swapped the order of the rows in the last test case. And I just noticed now the # notation... Would you mind clarifying it all? Those signs are nowhere defined in the challenge ^^' \$\endgroup\$ – V. Courtois Aug 13 at 14:52
  • \$\begingroup\$ OH ; and by re-reading all the text I saw that your & is strange: why does 0&0 get 1?? \$\endgroup\$ – V. Courtois Aug 13 at 14:53
  • 1
    \$\begingroup\$ @V.Courtois The "&" is not an &, it is an iff/not xor \$\endgroup\$ – tjjfvi Aug 13 at 14:54
  • \$\begingroup\$ Oh my bad then, I didn't know for this one. \$\endgroup\$ – V. Courtois Aug 13 at 14:56
  • \$\begingroup\$ @V.Courtois Tomorrow I’ll revise the test case format \$\endgroup\$ – tjjfvi Aug 14 at 0:38
  • \$\begingroup\$ @V.Courtois I explained & slightly revised the notation; is it clearer now? If you have any suggestions, they would be very welcome. \$\endgroup\$ – tjjfvi Aug 14 at 12:30
  • \$\begingroup\$ Ah yeah, it looks clearer now. The test case of length 8 is really helpful in the process, too, for guys like me that in general read the test cases before reading what is the actual challenge about :) Let's hear other points of view about this challenge, for my part I don't see any problem now. \$\endgroup\$ – V. Courtois Aug 14 at 12:38
  • 1
    \$\begingroup\$ You can remove the "Exception: if there are 0 inputs, there must be 1 row." line, \$2^0=1\$. \$\endgroup\$ – Erik the Outgolfer Aug 15 at 22:16
  • \$\begingroup\$ For languages that support ND array, a ND array (each dimension has size 2) would be a natural representation of a N-ary truth table. \$\endgroup\$ – user202729 Aug 16 at 4:44
  • \$\begingroup\$ In your example is "1 1 1" = "(1, 1) -> 1" or "1 <- (1, 1)"? \$\endgroup\$ – user202729 Aug 16 at 4:46
  • \$\begingroup\$ Also: do you know any polynomial time solution to this problem? \$\endgroup\$ – user202729 Aug 16 at 4:48
  • \$\begingroup\$ @EriktheOutgolfer shame. I'll fix that. \$\endgroup\$ – tjjfvi Aug 16 at 13:16

Planting Steiner Trees

In the following we are talking about Steiner trees, which are similar to minimal spanning trees: The goal is connecting all nodes via some paths such that the resulting graph that is as short as possible. In contrast to minimal spanning trees when constructing steiner trees you can add additional nodes.

In the following we are talking about points in the real 2d plane and when we are talking about distances and lengths, we are talking about the euclidean distance.

Also, a graph will comprise a set of points where the edges are straight lines between pairs of those points. The length of a graph will be the sum of the length of all edges.

So a steiner tree is a shortest graph connecting all given points possibly with inserting additional points. The following image shows the difference between a minimall spanning tree (blue) and a steiner tree (red).

It is known that it is very difficult to find steiner trees.

enter image description here


Write a program that accepts a list of 2d points and tries to find/approximate a steiner tree of minimal length connecting those points by possibly introducing more points. (It does not have to find the an actual steiner tree.)

The program should output a list of all the points (including coordinates) of the constructed graphs, a list of all edges (including their lengths), the total length of the graph and a graphical representation of the grap.

The program should have a running time of no more than about half a minute for each of the examples on a reasonable computer.

You should also explain how your algorithm works.


The program must be evaluated on all the [NOT YET] given test cases. The score is the sum of the total length of all test cases. The lowest score wins.

Test cases


(cos(2*pi*a/9),sin(2*pi*a/9)) for a = 0,1,...,8


Meta: I need to find a good set of test cases. Suggestions are appreciated.

If you have any suggestions, feel free to edit/add. Any improvements of the text are appreciated too.

@El'endia Starman Pointed out some interesting n-gon configurations

  • 3
    \$\begingroup\$ It is known that Steiner trees for regular n-gons where 7 <= n <= 12 are simply the n-gon with one side removed. 4,5,6 all have interesting configurations though. \$\endgroup\$ – El'endia Starman Oct 31 '15 at 0:03

Shortest Persistent Object in 5-Char JS

The []+=` subset of JavaScript is known to be Turing-complete. A key part of the construction is obtaining persistent objects whose properties can be set and retrieved in a loop.

Most expressions won't evaluate to constant values. For example, [] != [] when compared by reference. However, some expressions, such as [].name, return the same object every time they are evaluated.

The Task

The following should hold when e is substituted with your submission:

  • (e) instanceof Object (this includes functions and arrays)
  • (e) == (e)

This is , so the shortest valid submission (measured in bytes) wins.


Cleaning the dishes

In this task, you will be given a bar of soap with a width of 1 or more units, which will be inputted as an integer. You will also be given a plate, which you will have to clean, using the soap as few times as you can. The plate will be inputted as a an array of 2 different characters, one of which is the 'dirty' character, and one of which is the 'clean' character. The plate will be at least 1 character. You will have to output an array with the 'clean' character representing the plate, and a third unique character to represent in what positions the bar of soap was placed. None of these 3 unique characters may be whitespace.

How much the soap cleans:

n//2-1 on each side for odd n
n//2-1 on the left side of the soap bar for even n
n//2   on the right side of the soap bar for even n


An integer greater than or equal to 1. A series of 2 unique characters to represent clean portions and dirty portions. Here, '=' represents a dirty portion, and '-' represents a clean portion. '+' represents where the soap was placed.


3 ===- : -+--
32 ================================ : ---------------+----------------
1 ==== : ++++
5 ----- : -----
4 -====- : --+---
3 -====- : --+-+-
7 === : +--
6 - : -
6 -==-===- : ---+----
5 -==--==- : ---+--+-
3 -==--==- : --+--+--


  • There are multiple solutions. Any one of them are acceptable, as long as they use the soap the minimum amount of times possible.
  • This is a contest, so the shortest answer in bytes wins!
  • The plate may only be non-whitespace characters, and have 2 unique characters.
  • The soap may only be one non-whitespace character, unique from the other 2 used in the plate.
  • Standard loopholes are not allowed.

Posted: Cleaning the dishes

  • \$\begingroup\$ If "soap input may only contain the characters '0' through '9', and may be multiple characters", then can it not be passed as an integer argument to a function? \$\endgroup\$ – Unrelated String Sep 4 at 4:15
  • 1
    \$\begingroup\$ i already specified rules about soap input in the first paragraph, so i will erase that rule. \$\endgroup\$ – girobuz Sep 4 at 20:34
  • \$\begingroup\$ There seem to be multiple possible outputs, e.,g.: 3 =-=-= could be either +--+- or -+--+, yes? If that is true, can we output any of them? \$\endgroup\$ – Chas Brown Sep 7 at 23:34
  • \$\begingroup\$ Yes, any output is acceptable, as long as it works, and is the minimum. \$\endgroup\$ – girobuz Sep 7 at 23:53

Battleship KotH

This is a pretty rough idea to start but I figured I would drop it in the sandbox so that people can start to think about it and I will remember to do it.

The idea here is a that combines the game, battleship with .

The rough idea is that two enemies would face off, each turn irradiating a location in their opponents source code. Then the opponents source code would be recompiled and then try and attack back.

Some additional thoughts I've had:

  • We will likely want to limit the size of the board to a specific rectangular size

  • I would like there to be a feedback from shooting your opponent (in the game battleship this is hit/miss) so that you are doing more than just firing randomly. Perhaps programs might irradiate a single bit (flipping its value) and get back its value before it was irradiated.

Language choice is a bit tough since I would like something multipurpose and flexible but I don't want to have to deal with the security issues that are involved in compiling and running a fully featured programming language.

  • \$\begingroup\$ radiation-hardening tends to work best with deletion. This is going to need a maximum byte count to be fair, otherwise the best strategy is excessive amounts of whitespace and comments. Love the idea though. \$\endgroup\$ – Beefster Sep 17 at 14:22
  • \$\begingroup\$ You don't actually have to limit yourself to a specific language on this one. It wouldn't be that hard to use a shell script to run whatever languages are available. One question though: is each program able to read the source code of the other or is each attack supposed to be blind? If you're worried about security, you could run the controller in a docker container or VM. \$\endgroup\$ – Beefster Sep 17 at 14:26

Injection from two strings to one string

  • \$\begingroup\$ Do you think that a reasonably number of languages won't implement the following: convert the strings into numbers (e.g. treat each character as a base 128 digit) then give a resulting string of those two numbers joined by some other character? I haven't spent too long thinking about it but that seems very short in most languages. I suppose there are other variants though where you map characters to some subset and then join them. \$\endgroup\$ – FryAmTheEggman Sep 24 at 20:42
  • 2
    \$\begingroup\$ @FryAmTheEggman I imagine the solution used is going to depend on the language: what builtins it has, if it's more high-level or low-level, etc. But there may well end up being a prevalent algorithm. \$\endgroup\$ – negative seven Sep 24 at 20:57
  • \$\begingroup\$ Why strings? Lists of integers, (even restricted to a range) work as well but don't have the complexities that strings do when it comes to printables etc. I feel like the simpler challenge is going to be the better one. \$\endgroup\$ – Wheat Wizard Sep 26 at 3:30
  • 1
    \$\begingroup\$ @FryAmTheEggman Don't worry, I've thought of a totally different approach that I think would be shorter for many languages. \$\endgroup\$ – xnor Sep 26 at 4:46
  • 2
    \$\begingroup\$ @SriotchilismO'Zaic Restricting the character set seems to me like a reasonably simple detail, while making it about strings encourages creativity with string operations, converting to string representations, etc. Also, I personally think string input/output is much more appealing to look at and easier to consume than a list of numbers. \$\endgroup\$ – negative seven Sep 26 at 14:38

Code Golf Measurer © 2019

Hexdumps used with xxd look something like this:

00000000: 666f 6f20 6261 7220 7370 616d 2065 6767  foo bar spam egg
00000010: 730a                                     s.

Your task is to convert a hexdump in this form in to the number of bytes used.


  • Usual loopholes forbidden.
  • This is , so shortest valid answer in bytes wins.
  • You may or may not include the newline at the end of text (0a). This means that if the hexdump ends in a newline (0a), that input may have it's output reduced by one.
  • An empty input must output 0.

Test cases:

00000000: 4865 6c6c 6f2c 2077 6f72 6c64 2120 4865  Hello, world! He
00000010: 6c6c 6f2c 2077 6f72 6c64 210a            llo, world!.

returns 27 or 26

00000000: 0a                                       .

returns 1 or 0

00000000: 6368 616c 6c65 6e67 650a                 challenge.

returns 10 or 9

00000000: 4865 6c6c 6f2c 2077 6f72 6c64 21         Hello, world!

returns 13

returns 0


  • Is this clear?
  • Is this a duplicate?
  • Other tags?
  • 1
    \$\begingroup\$ Does the extra rule mean that the input can have an optional trailing newline, or that the results in all of your test cases could be reduced by 1? If you mean the former I recommend adding a test case that doesn't end with a newline. If you mean the latter then I recommend explicitly saying the file will end with a newline character. Also I suppose this is a string challenge. Thanks again for using the sandbox :) \$\endgroup\$ – FryAmTheEggman Oct 3 at 20:55
  • \$\begingroup\$ @FryAmTheEggman It means that all test cases could be reduced by one. This was intended as a code golf byte counter, and the newline most certainly isn't usually included. I'll clarify this and add another test case to highlight it. \$\endgroup\$ – gadzooks02 Oct 4 at 15:17
  • \$\begingroup\$ So: discard all the input except the last line, and parse hex? Or just output the last line and claim that your output is in hex? IMO it would be a more interesting problem with xxd input, where the last line is not present. \$\endgroup\$ – Peter Taylor Oct 5 at 9:00
  • \$\begingroup\$ @PeterTaylor If I were to switch to xxd, would that be a valid edit, or would that be too big a change such that I would have to post another challenge? \$\endgroup\$ – gadzooks02 Oct 5 at 9:45
  • \$\begingroup\$ I'm sure far more significant edits have been made to sandboxed challenges in the past. \$\endgroup\$ – Peter Taylor Oct 5 at 13:10
  • \$\begingroup\$ @PeterTaylor In that case, edited. \$\endgroup\$ – gadzooks02 Oct 5 at 14:52

ASCII Sum of your code

Encoding is nice, adding things is also nice. Let's do both !

Your task will be to create a program that read itself, convert every of its character into ASCII values and return the sum of those numbers.


Let's say your program is Hello, world !. Convert every character into ascii values

H  e   l   l   o   ,  (space) w   o   r   l   d   (space) !
72 101 108 108 111 44 32      119 111 114 108 100 32      33

Now, sum everything into a meaningless very useful value

72 + 101 + 108 + 108 + 111 + 44 + 32 + 119 + 111 + 114 + 108 + 100 + 32 + 33
= 1193

Here it is, Hello, world! returns 1193 !


  • The code have to read itself and calculate the result
  • Standard loopholes are not allowed
  • This is codegolf, so the fewer bytes wins.
  • Non-standard languages with non-ASCII characters should use their own codepage's encodings (Thanks for @Veskah for this rule)


  • Is the challenge clear enouth ?
  • Is there an already existing challenge like this one ?
  • is this considered as a duplicate of this challenge ?
  • 2
    \$\begingroup\$ I would probably have non-standard languages use their codepage's encodings (pretty much all of them should be 8 bytes) to crunch their output. The big hammer approach would be to ban non-ASCII languages but I would not recommend that. \$\endgroup\$ – Veskah Oct 23 at 14:06
  • 3
    \$\begingroup\$ Requiting the code to read itself and do the calculation is a non-observable requirement. Since it seems you don't want programs that just hardcode the value, I think the best way to be just to require the program take in an input string to use. Regardless, I don't really see room for interesting golfing in the challenge, since pretty much any normal-ish language has built-ins to take ASCII values and compute sums, and weird languages that don't have already done these as subtasks for many many challenges. \$\endgroup\$ – xnor Oct 25 at 0:52
  • \$\begingroup\$ @xnor Does this challenge with string input already exist ? \$\endgroup\$ – The random guy Oct 25 at 7:06
  • 2
    \$\begingroup\$ I don't remember an exact one, but I'm finding very close ones: averaging ASCII values and summing then counting binary 1's, which was closed as a duplicate of one without the character adding. I also found an unrestricted quine challenge with the same task as yours. So I think there's a good chance this would be closed as a duplicate either way. \$\endgroup\$ – xnor Oct 25 at 7:11
  • 1
    \$\begingroup\$ Yup, the last one is quite the same as mine. Duplicate it is then. \$\endgroup\$ – The random guy Oct 25 at 7:13

Java vs C++

Now posted at Time to settle this: Java vs C++

  • \$\begingroup\$ How vital is the validation to the challenge? \$\endgroup\$ – Unrelated String Aug 27 at 21:01
  • \$\begingroup\$ @UnrelatedString I think it's fairly integral if the story is considered. Gotta inform the user that they're feeding you crap. Also it should add an extra element of challenge. \$\endgroup\$ – Mr Redstoner Aug 27 at 21:07
  • 3
    \$\begingroup\$ @MrRedstoner Validation is generally considered tedious by the users of this site, rather than challenging. I'd recommend reconsidering - clearly the validation code could make use of the submissions as a subroutine. There are also a couple near dupes 1 2 but I haven't found a precise dupe. That said, thanks for using the sandbox! \$\endgroup\$ – FryAmTheEggman Aug 28 at 0:36
  • 1
    \$\begingroup\$ getHTTP would result in... get_h_t_t_p? get_http? Error? Some other thing? \$\endgroup\$ – Chas Brown Aug 28 at 1:42
  • \$\begingroup\$ @ChasBrown should be get_h_t_t_p, I shall add that. @FryAmTheEggman While I considered it part of the story, if those are the standards I figure I'll remove it and say the validation was done by a previous part of code. \$\endgroup\$ – Mr Redstoner Aug 28 at 5:24
  • \$\begingroup\$ "If it is neither, output/return a falsey value." I would change this to something like "If it is neither, any unspecified behavior is fine (return a falsey value; give an error; try to convert it somehow anyway; etc.)." As mentioned by @FryAmTheEggman, validation is usually considered a distraction of the actual challenge (and can sometimes even double the code of the program/function for those answering), so most challenges assume the given input will always be valid. Apart from that the entire challenge looks fine, so +1 from me. Thanks for using the Sandbox! :) \$\endgroup\$ – Kevin Cruijssen Aug 28 at 9:32
  • \$\begingroup\$ @KevinCruijssen Dang it missed that during the edit. Thanks for telling me! \$\endgroup\$ – Mr Redstoner Aug 28 at 10:42
  • \$\begingroup\$ What should be returned from an input of a__b (two underscores)? \$\endgroup\$ – Value Ink Aug 29 at 1:03
  • 1
    \$\begingroup\$ @ValueInk That would be invalid input. 'You may assume all input to be valid'. Therefore I refer you to the ANSI C standard for undefined behaviour. \$\endgroup\$ – Mr Redstoner Aug 29 at 6:00

Can Jimmy escape the ghosts?

Posted: Can Jimmy escape the ghosts?

  • 1
    \$\begingroup\$ S'all good, no problem \$\endgroup\$ – Veskah Oct 17 at 14:05

Signpost reading

Note: I didn't invent this challenge, I came across it elsewhere and thought it would fit here. I haven't found it already posted here, but there's a perfectly fine chance that I merely overlooked it. It's also defined in an interresting manner IMO. Anyway, I'll let the challenge speak for itself.

Challenge definition == Example input/output:

Input 0

The hero was deep inside the dragon’s lair.
But he was not afraid; he knew what was coming.
Each dragon lair has some crossroads. At each crossroad, one can go either left or right.
At each crossroad there is a signpost, indicating what is to the left, and what is to the right, always in the same format.
One direction leads to the dragon.
If the hero,in full armour, went into the dragon’s bedroom, he would surely wake him up and become breakfast in bed.
So, the hero will definitely choose the other option.
The hero always reads this signpost into a  single line, by itself.
Oh, here comes the first crossroads, thought the hero to himself.
Left to dragon. Right to princess.
Oh no, what is this sorcery!?
What heroes don’t know, is that the signposts are cursed.
Whoever reads one, forgets which of the two options he definitely didn’t want to pick.
So the hero needs your help - Every time he manages to read a signpost,tell him where he needs to go.

Output 0

Right, to the princess!

Input 1

The story contains at most 100 lines, none of which are over 100 characters long.
The signposts are always read into a single, separate line, and strictly follow the following format:
Left to x. Right to y.
Where x,y are non-empty strings made up of letters of the english alphabet, one of them is ’dragon’, and the other is NOT ’dragon’.
This line must have no missing, or extra, spaces.
Notice that the above example is not a valid signpost, as it violates ’one of x,y is dragon’.
Often, heroes just mentally prepare for the inevitable signpost they will face.
Right to dragon. Left to princess.
Hm, on a real signpost the directions would probably be the other way around,thought the hero.
Wait, what is this before me!?
Left to dragon. Right to goodluck.
Left to YouWillNeedIt. Right to dragon.
What is happening!? Where should I go???
Left to havefun. Right to dragon.
Left to dragon. Right to dragon.
What the hell kind of sign was that?

Output 1

Right, to the goodluck!
Left, to the YouWillNeedIt!
Left, to the havefun!


Standard input/output rules apply, standard loopholes are forbidden.


Has this been done?

Is this sufficient for a definition?

Tags I'm thinking of: string, decission-problem, any suggestions for others/more fitting ones?

  • 1
    \$\begingroup\$ Questions: a) what if both x and y are 'dragon'? b) may x or y include capital letters? \$\endgroup\$ – Artemis supports Monica Oct 28 at 23:18
  • \$\begingroup\$ @ArtemisFowl a) that violates 'the other is NOT dragon', therefore making it an invalid signpost (note how nothing is output for those), I may add that to the examples b) yes they can, I'll modify the examples to show that. \$\endgroup\$ – Mr Redstoner Oct 29 at 7:27
  • \$\begingroup\$ a) oh my bad b)cool \$\endgroup\$ – Artemis supports Monica Oct 29 at 20:18

Substitute Unprintable ASCII Characters

Have y'all ever written an answer with unprintable ASCII characters in it and wished that there was an easy way to represent those characters in a printable way? Well, that's why the Control Pictures Unicode block was invented.

However, manually substituting these characters into one's answer is time-consuming, so that's what today's challenge is about: swapping out the nasty invisible characters for nice, readable characters.


You will be given strings that contain a mix of ASCII-only characters (i.e. the UTF-8 code point of each character will be in the range: \$0 \lt char \le 127\$).


For all unprintable characters, replace it with its corresponding character in the Control Pictures Unicode range.

In other words:

  • Characters in the range \$0 \lt char \lt 9\$ are replaced with their corresponding character
  • Vertical tabs and newlines (9 and 10) aren't replaced
  • Characters in the range \$11 \le char \lt 32\$ are replaced with their corresponding character
  • Spaces (32) aren't replaced
  • The delete character (127) is replaced with its corresponding character:


Characters are given as escapes for nice formatting here, but each character will be replaced with the unprintable character

In -> Out
\x1f\x1c\x1f\x1e\x1f\x1e\x1f\x1f\x1e\x1f\x1e\x1f -> ␟␜␟␞␟␞␟␟␞␟␞␟
Hello\x07World! -> Hello,␇World!
\x01\x02\x03\x04\x05\x06\x07\x08\x0c\x0b\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f\x7f -> ␁␂␃␄␅␆␇␈␌␋␎␏␐␑␒␓␔␕␖␗␘␙␚␛␜␝␞␟␡


  • All standard loopholes are forbidden
  • Character substitutions must be made according to the Control Pictures Unicode block


This is code-golf so the answer with the fewest amount of bytes wins.

Test-Case Generator

I have provided a test case generator for y'all. It prints inputs in the way they will be passed to your program and outputs the expected result.

Try it online!

  • \$\begingroup\$ "DEL" (ASCII 127) is also unprintable. Also, did you mean 0≤char≤127? \$\endgroup\$ – Bubbler Nov 15 at 8:00
  • \$\begingroup\$ Updated! (I forgot DEL wasn't printable) \$\endgroup\$ – Jono 2906 Nov 15 at 8:04
  • \$\begingroup\$ I think you need to give test input as JSON (i.e. with escapes) \$\endgroup\$ – Adám Nov 15 at 8:46
  • 1
    \$\begingroup\$ Space has a substitution character (). Should it be replaced? I think you should clearly state that ≤ (or < 32) and 127 should be replaced. \$\endgroup\$ – Adám Nov 15 at 8:48
  • \$\begingroup\$ Updated accordingly. \$\endgroup\$ – Jono 2906 Nov 16 at 1:33

A Spherical Die


I have a spherical die, but it's a cheap one so it doesn't work properly. When I roll it, it doesn't always land directly on a "face" marking, but instead can result in an ambiguous result ("is that a 6, a 4 or a 2?")


Assume the die is a perfect, evenly-weighted Unit sphere (i.e. all points on the surface are radius 1cm from the center) , such that a "roll" can result in any point on the sphere being the uppermost point (the "roll value").

Assume that, if the die is placed or rolled such that 1 is at the "north pole", the conventions of a normal die will follow, i.e:

  • 6 will be at the "south pole"
  • 4, 5, 3, 2 will be on the "equator", clockwise in that order, equidistant around the sphere.

So, before it's rolled, the die looks like this:

image of die

The Challenge

Given a simulated roll of the die with the conditions above (i.e. coordinates representing the top of the die after it's rolled), identify the closest value (1-6) to that point (i.e. what the roll value should resolve to).


A co-ordinate on the sphere.

There are a few co-ordinate systems used for spheres, the two I'm familiar with (and so will provide examples in) are as follows:

  • P(1, φ, Θ) where φ is the "azimuth angle" (0..360), Θ is the "polar angle" (0..180)

  • P(x,y,z) where \$x^2+y^2+z^2=1\$

(note: the conversion between the two is: x = cos(φ)·sin(Θ); y = sin(φ)·sin(Θ); z = cos(Θ))

for clarity:

  • roll "1" is at P(1,n,0)
  • roll "2" is at P(1,270,90)
  • roll "3" is at P(1,180,90)
  • roll "4" is at P(1,0,90)
  • roll "5" is at P(1,90,90)
  • roll "6" is at P(1,n,180)


The nearest value (1-6) to that point. If the point is equidistant to two or more points, output any one of them.

Usual exclusions etc. apply.

  • \$\begingroup\$ Does anyone know the maths for this? Feel free to edit it in! \$\endgroup\$ – simonalexander2005 Nov 22 at 9:40
  • \$\begingroup\$ I'm not sure I understand: You want us to generate a random point on a sphere and output the face of the die it corresponds to? \$\endgroup\$ – flawr Nov 22 at 9:57
  • \$\begingroup\$ yeah, so generate a random point on the sphere, then find the nearest "face" - i.e. the nearest of the 6 points (top, bottom, 4 points on opposite sides around middle) \$\endgroup\$ – simonalexander2005 Nov 22 at 11:11
  • \$\begingroup\$ This will be exactly equivalent to a uniform distribution over 6 values, just based on the symmetry of the situation. \$\endgroup\$ – AlienAtSystem Nov 22 at 12:33
  • \$\begingroup\$ @AlienAtSystem yes, all outcomes are equally likely; but the challenge is determining which number any given point on the face of the sphere is closest to \$\endgroup\$ – simonalexander2005 Nov 22 at 13:04
  • 2
    \$\begingroup\$ That's not the challenge as posted. Right now, it's "Takes no input, returns the number the (internally generated) random point is closest to" which is, under the consensus of no unobservable requirements simply equal to "Takes no input, returns uniform random value from 1-6". If you want the challenge to be "Input is point on sphere, output is number it's closest to", then write that. \$\endgroup\$ – AlienAtSystem Nov 22 at 13:09
  • \$\begingroup\$ @AlienAtSystem I've edited to try and make it clearer what I'm looking for. Is it clearer now? \$\endgroup\$ – simonalexander2005 Nov 22 at 13:15
  • \$\begingroup\$ It's clearer that my point still stands. Look, "Make Voronoi cells on sphere" and "Generate uniformly random points on sphere" are both good challenges. But when put together like that, they annihilate each other and give you an extremely quick shortcut right from Input (None) to output (a die roll) that doesn't require calculation of either part. \$\endgroup\$ – AlienAtSystem Nov 22 at 13:21
  • 2
    \$\begingroup\$ @AlienAtSystem thanks for the feedback, I'd never heard of a Voronoi cell before. What I'm asking, then, is "generate a random point on a sphere and say which Voronoi cell that point is in". Can you explain why that doesn't work? Note that I'm asking for both the point and the cell to be output, not just the cell - otherwise I agree, given the "no unobservable requirements" rule it would be possible to just generate a random number and pretend you'd done it properly (although that would be against the spirit of it) \$\endgroup\$ – simonalexander2005 Nov 22 at 13:24
  • \$\begingroup\$ Would it be better for the point on the sphere to be the input, then? \$\endgroup\$ – simonalexander2005 Nov 22 at 13:27
  • \$\begingroup\$ If you want the challenge to be about finding the points it's closest to, yes. \$\endgroup\$ – AlienAtSystem Nov 22 at 13:31
  • \$\begingroup\$ I want it to be a good challenge on this theme, whatever that would look like :) \$\endgroup\$ – simonalexander2005 Nov 22 at 13:33
  • \$\begingroup\$ Although I don't think the current challenge is bad, it's usually best to not have multiple challenges into one nor multiple outputs (since some languages aren't able to output more than once very easily). The two challenges are: 1. Generate a random coordinate on a sphere (in whichever coordinate system you want); 2. Given a (random) coordinate on a sphere, output the dice-value closest to it. No. 1 already is a challenge, so I agree it might be better to rewrite it to challenge No. 2. I do like the general idea though, so +1 from me. \$\endgroup\$ – Kevin Cruijssen Nov 22 at 14:36
  • \$\begingroup\$ It would also need some info about the size of the sphere, and what to do when the coordinate is exactly in the center between two or three poles. \$\endgroup\$ – Kevin Cruijssen Nov 22 at 14:39
  • \$\begingroup\$ @KevinCruijssen Thanks, that's helpful. \$\endgroup\$ – simonalexander2005 Nov 22 at 14:40

OEIS A125959

https://oeis.org/A125959 is a sequence I submitted. It is the following array, which then repeats:

1 2 3 4 5 6 7 8 9    
2 4 6 8 1 3 5 7 9    
3 6 9 3 6 9 3 6 9    
4 8 3 7 2 6 1 5 9    
5 1 6 2 7 3 8 4 9    
6 3 9 6 3 9 6 3 9    
7 5 3 1 8 6 4 2 9    
8 7 6 5 4 3 2 1 9    
9 9 9 9 9 9 9 9 9

This is a rather useful array for quickly calculating the digital root of the product of any two numbers (i.e the iterative sum of the digits of the product). See the OEIS link if you're interested in the details.

The challenge is to print the array in the shortest number of bytes.




The above array. It can be output as strings with new lines, or as a nested array, or an array of strings; but not as a single-line sequence (i.e. the 2d-nature of the array must be reflected in your output).

  • 4
    \$\begingroup\$ So it's the multiplication table mod 9, except 0s are 9's? \$\endgroup\$ – xnor Nov 25 at 12:58
  • \$\begingroup\$ @xnor is it? I hadn't spotted that before. Does that stop it being an interesting challenge? \$\endgroup\$ – simonalexander2005 Nov 25 at 13:49
  • 1
    \$\begingroup\$ I believe it does (because it is "create a 10x10 table of the function (-~a*-~b-1)%9+1" now). \$\endgroup\$ – my pronoun is monicareinstate Nov 25 at 14:05
  • 2
    \$\begingroup\$ I think it makes it too similar to generic print-a-multiplication table challenges, but others might disagree. \$\endgroup\$ – xnor Nov 26 at 2:10

Bake the cookie

Quick intro

So i was playing cookie clicker yesterday, and I thought about something. We keep producing cookies, without any loss. What if your cookies failed? This is where I thought about a clicker that would cook a cookie. Don't click too much, or the cookie will be overcooked!


Your task will be to create a function that will "bake" a cookie :

  • Your function will have to randomly select a number between 5 and 10 : it will establish the cooking duration of your cookie (and so, the number of time you'll have to call the function to cook your delicious cookie).
  • Each time you call that function, it will iterate the baking process of your cookie.
  • Your function should return "Undercooked" if your cookie is not fully cooked, "Overcooked" if you ... overcooked it, and "Cooked" when the cookie is baked just right.


Since I'm bad at explaining things, an example will show you more clearly what needs to be done. Let's call my function bake() :

bake()    // The random number generated is 6, so i need to call my function 6 times





bake()    // We hit the 6th function call, the cookie is baked.

bake()    // The 7th call overcooked the cookie. Congratulation, you ruined it.


  • The random number of iterations has to be set the first time you call the function. It has to be between 5 and 10 (inclusive).
  • A cookie has to be undercooked before being cooked, and has to be cooked before being overcooked. The 3 steps have to be reachable. A cookie can't uncook itself, therefore you can't go from cooked to undercooked, or from overcooked to cooked (it's too late, you ruined the cookie anyway).
  • The function can have as many parameters as you please.
  • Classic rules apply, no standard loopholes
  • This is codegolf, so the shortest code wins.


  • Is the challenge clear enough ?
  • Should I go with this method to iterate the "baking" process ?
  • Are there some rules I could add to make it more exciting ?
  • Does this challenge exist already ?
  • Should we bake pies instead ?
  • \$\begingroup\$ I'm assuming bake() will take no parameters and will have to store the count somehow, which means you might want to include some rules about file and global variable I/O. I also did a small editing pass. \$\endgroup\$ – Veskah Dec 2 at 16:14
  • \$\begingroup\$ @Veskah I never thout about restricting bake()'s parameters, gonna edit the rules to include this particulatiry. Also, thanks for the edits. \$\endgroup\$ – The random guy Dec 3 at 8:12

Universal Self-correcting Program

The idea here is to make a program that can tolerate errors in its own code, while still functioning correctly.

Since "error" is too broad, we will define it by a single bit flip. Of course, more tolerant versions, that could accept swapping any character with any other character would still be valid.

This program is universal in the sense that you can write any other self-correcting program (with the same tolerance) -- more on that later.


1) This program takes as input a triple-redundancy string of characters, and outputs a corrected string.

2) This program executes correctly with any bit flip in its own code.

(1) Triple redundancy codes

A triple redundancy code consists of simply repeating each bit, character or byte 3 times. In this case we use characters.

Correction is done by taking the majority of the characters, so (A,A,B) is corrected to A, (A,B,B) is corrected to B and so on.

AAA => A
AAB => A

This is a very crude an inefficient code for correcting single bit errors, but it is the least complex, which is why I think may be the best choice here. Hamming codes are better but a little more complex.

(2) Error tolerance

Our program will be defined as error tolerant if it performs the desired decoding function for any single bit flip in its own code. It may take longer for some inputs or when some flips occur, but it should always terminate.

Putting it together

The error-tolerant program can receive as input a (possibly faulty) program, and outputs a error-free program. Therefore, if a single-bit error occurs anywhere in the system comprised of (decoder,input program), a corrected program will still be output.


I don't actually know if this is possible, quite possibly it won't be achievable in every language. If it is too hard, we may relax the tolerable errors.


The score will reflect the reliability of your program to errors. Tolerance is simply the number of bit flips you code accepts anywhere. It must be at least 1 (accept 1 bit flip anywhere). Size is the length of your program in bytes.

The score is Score = Size / 2^Tolerance

Lowest score wins.

Note: Several other challenges are possibly solved by solving this one (which would make sense given its universality!) by hardcoding the input.

Detect if your program has been mutated

Write a program that always outputs “2012” - even if it's modified!

This solves the "Who Watches the Watchmen?" problem involved in error correcting programs, like in this challenge:

Meta radiation hardener

since the decoding program itself tolerates errors (what good would be an error correcting program that is itself in error? :p).

  • 2
    \$\begingroup\$ Check the radiation-hardening tag for duplicates and rules clarifications, too. \$\endgroup\$ – AdmBorkBork Mar 7 '18 at 19:17
  • \$\begingroup\$ @AdmBorkBork Thanks, I wasn't aware of that. It appears no one has proposed a Universal radiation hardener yet (this is universal only in the sense of bit flip errors; those are actually a good model for radiation though!). \$\endgroup\$ – Real Mar 7 '18 at 19:30
  • 1
    \$\begingroup\$ Again Lenguage win lol \$\endgroup\$ – l4m2 Jan 8 at 14:53
  • \$\begingroup\$ Even though your scoring involves code length you should use code-challenge instead of code-golf for challenges that are not solely scored by code length. \$\endgroup\$ – Laikoni Jan 10 at 20:14

Count Syllables

The goal of this challenge is to write a program that can count the syllables in a word as accurately as possible.


On STDIN, your program will receive a number X followed by X lines, each containing a single word. Simple enough. (Should there be a limit on the size of X?) The words will come from this list.



Your output should be to STDOUT and have X lines. On each line should be the number of syllables counted in that word.



To score you program, it will receive a long secret list of words to test. All programs will receive the same list of words. For each word, the number of syllables that your program got wrong will be added to the score of the program. If it output a 4 or a 2 when the word had 3 syllables, then one point will be added. If it said a 15 instead of a 3, then 12 points will be added to the score. The lower the score, the better.

For example, if for the above input your program output 3 2 2 2 (which would be produced by a program that counts strings of vowels), then the program would receive a score of 2.


Your program should not access any external files (such as the word list). Also, your program should be no more than 5,000 bytes long (is this a reasonable limit?).

The winner will be the person whose program has the lowest score, therefor the most accurate syllable counter. The deadline for submissions is [some time at least a month away].


I am open to all constructive criticism. Is 5,000 bytes a reasonable limit for the program size? How long should the official scoring test be? How long should the deadline be?

  • 10
    \$\begingroup\$ This has one major flaw: the output is subjective. How many syllables do these words have? Every; victory; hierarchy; desire; oil; hour; poem. The only real way I see to work around this is for you to produce a marked-up version of the word list. \$\endgroup\$ – Peter Taylor May 29 '12 at 20:40
  • \$\begingroup\$ I was really worried about that, and I don't see a way around it. \$\endgroup\$ – PhiNotPi May 29 '12 at 20:42
  • 1
    \$\begingroup\$ I personally would love to see more language processing challenges. I agree with @PeterTaylor on the difficulty of some words. Perhaps taking a specific text(s) and identifying explicitly in the challenge which words will have how many syllables? \$\endgroup\$ – Gaffi Jun 8 '12 at 3:34
  • 2
    \$\begingroup\$ @PeterTaylor ...Or maybe you could filter ambiguous words out of the reference list? \$\endgroup\$ – user16991 Feb 8 '15 at 1:19
  • 1
    \$\begingroup\$ What's the point of the first line of input? \$\endgroup\$ – msh210 Apr 27 '16 at 20:05
  • 2
    \$\begingroup\$ If you provide a reference list, A hyphenated reference list, and hide a secret list which may or may not include members of the reference list, this would be a reasonable challenge \$\endgroup\$ – Rohan Jhunjhunwala Sep 17 '16 at 0:05
  • \$\begingroup\$ Do you plan to post this? If not, I'd be happy to adopt it. (If you don't respond within two weeks, by community standards, I'm allowed to do so.) \$\endgroup\$ – MD XF Aug 18 '17 at 3:20
  • \$\begingroup\$ The example of inaccurate program that would score 2 - did you mean to output 3 1 1 2 rather than 3 2 2 2? \$\endgroup\$ – Heimdall Nov 9 '17 at 18:31
  • \$\begingroup\$ A reference list could be dynamic: potential contestants can ask for words of their choice to be added to the list. They won't know what's on the secret list but will try to make their programs as accurate as possible (according to your syllable count) so they should always be able to ask for specific words they are not sure about. Of course, you could make it in different language. In my language, Slovene, it's much clearer how many syllables words have. How about Solresol, haha! \$\endgroup\$ – Heimdall Nov 9 '17 at 18:38
  • \$\begingroup\$ I am going to adopt this if you don''t respond \$\endgroup\$ – Christopher Dec 20 '17 at 16:48

Play Simple 2-Dimensional Minecraft

Recently I found this video of "HansLemurson" showing a computer that was built in minecraft, which runs minecraft. He is playing minecraft on a computer that was built in minecraft that is running on his computer. To be specific, it is a two dimensional version with an 8x8 grid of cells. There is gravity, block placement, and even jumping. It is worth noting that the computer is single purpose. The same person has built programmable computers, but making them single purpose allows the computer to be much smaller.


The minecraft world is an 8x8 grid (one horizontal and one vertical dimension). The grid is comprised of either Xs (representing blocks) or empty spaces. The player is an X that is blinking on and off about once every second.

There are two modes in the game, controlled by a toggle switch. The first mode is movement. This is controlled by a WASD-like button arrangement. If the player chooses to move left/right/down, the computer checks to see if the space immediately in that direction is empty. If so, then the player moves into that space.

If the player chooses to move up, then the computer checks that the block underneath the player is solid. If so, then the player moves upward two units. Notice that this can propel the player into a solid block. If this happens, the player is obscured by the solid block, but can still move to an empty block next to him. When the player is inside on a solid block, the game continues as if the block isn't there, although the block is still there once the player leaves it.

After each move, the player falls down one unit if there is empty space there. This simulates gravity. This is also why moving up moves up two units, so that the gravity makes a net movement of up one unit. Gravity does not cause the player to fall all of the way to the ground, just one unit.

The second mode is block placement. In this mode, the same exact WASD buttons are used. Instead of moving the player, they toggle the state of the block in that direction. If the player presses "left" and there is a block there, then the block is destroyed. If there is not a block there, then a block is placed. Again after this move, the player is again subject to gravity. The blocks are not subject to falling.

Toggling the toggle switch does not count as a move, and does not invoke gravity.

The game board is a torus, so all actions (movement, block creation) can wrap around the board. The board does not scroll with the player. The player moves, and the blocks stay in the same place.

The challenge

You challenge is to write the shortest program that simulates this game. Your program should display and update the map correctly (with Xs as blocks, and with the blinking player). It should accept input from a button that toggles the state and four buttons for movement and actions. This is code golf.

There are imaginary bonus points for adding more features (block types, game size, etc) to your game.


  • 2
    \$\begingroup\$ With more complicated challenges I find that it helps to do a reference implementation so that you have a very concrete idea of how much work is involved. Aside from that, I like it. \$\endgroup\$ – dmckee Jun 3 '12 at 20:11
  • \$\begingroup\$ Is the blink rate selected to fit with the ANSI escape sequence? Either way I would explicitly allow that, because it's the obvious way to do it on compatible terminals. \$\endgroup\$ – Peter Taylor Jun 5 '12 at 7:14
  • \$\begingroup\$ The blink rate wasn't selected to be anything specific. I think that I will broaden the restriction. Maybe any blink rate between 3 blinks per second to 1 blink every 2 seconds. \$\endgroup\$ – PhiNotPi Jun 5 '12 at 20:21
  • \$\begingroup\$ @programmer5000 No, for two main reasons: First, challenges can go extended periods of time in the sandbox before they are posted and/or adopted. In the past I've posted challenges after not touching them for 4 years. Second, deleting this answer will not reduce lag, as deleted answers are still present, simply not visible. Users with sufficient rep will see all 4040 answers in the sandbox, and you will too once you earn the "view deleted answers" privilege. \$\endgroup\$ – PhiNotPi Apr 13 '17 at 18:15

I've Got The Key, I've Got The Secret

A cryptography challenge in 2 parts.

Part 1

Implement a pair of programs in any language (the two programs could be in different languages if you wanted) to encode and decode a string of plaintext.

Input and Output

The encoder must take the plaintext (and an optional key) and return an encoded string. The decoder must take the cyphertext (and an optional key) and return the plaintext exactly as it was given to the encoder.


  • The encoding and decoding code must be entirely implemented in the language - no libraries or cryptography functions may be used.
  • The code (encoder+decoder) cannot be longer than 1024 characters.

Part 2

Implement programs (multiple programs per answer, one answer per entrant) which crack your opponents encryption algorithms.


The cyphertext.


The plaintext that generated the ciphertext.


I will upvote all answers to part 1 which have working encryption and have obviously made an attempt at golfing their answer.

In order to be eligible to win, an entrant will have to have taken part in both parts of the question. Overall score will be (length of shortest program that cracks your code-(length of encoder+length of decoder)). Highest score wins and winning entrant's entries will be accepted on both questions.

  • 1
    \$\begingroup\$ The obvious place for this to fall flat on its face is if someone is able to implement AES or something similar within the 1024 character restriction. \$\endgroup\$ – Gareth Jun 13 '12 at 13:06
  • 1
    \$\begingroup\$ Probably better if the methods of the part one programs are disclosed in non-obfuscated language, though with the short length restriction this may not be necessary. \$\endgroup\$ – dmckee Jun 13 '12 at 15:23
  • 2
    \$\begingroup\$ Forget AES: RSA is easily doable. That aside, you need to define "crack" in part 2. \$\endgroup\$ – Peter Taylor Jun 13 '12 at 15:35
  • 1
    \$\begingroup\$ Also, it's not clear whether "optional key" means that it's optional to make the algorithm unkeyed (doesn't make much sense, I admit) or optional to supply it, in which case it uses a default key. \$\endgroup\$ – Peter Taylor Jun 13 '12 at 15:42
  • 1
    \$\begingroup\$ @PeterTaylor I just put optional in to leave it up to the implementer whether or not they wanted to have the key input or hard-coded (or use no key). I'd have thought everyone would have the key input into their program, but I didn't want anyone to feel forced into it by the spec. Hmm, if RSA is doable within the character restriction I'll end up with a load of unbreakable codes which would make for a pretty crap part 2. By crack I meant cyphertext goes in, some time later plaintext comes out. Would restricting the character count further help, or is this question beyond help? \$\endgroup\$ – Gareth Jun 13 '12 at 16:05
  • 3
    \$\begingroup\$ On that definition of crack, I can brute force for the length of the decoder plus a few bytes to iterate over all keys of the right length and some heuristics to check plausibility of the plaintext. The brute force cracker might even be shorter than the decoder if the decoder wasn't written in GolfScript... I think this question may be beyond help. \$\endgroup\$ – Peter Taylor Jun 13 '12 at 16:28
  • 3
    \$\begingroup\$ @PeterTaylor Okay, thanks. I like the 'build your own - knock everyone else's down' aspect of this question though. I'll have to find another area where it could apply. \$\endgroup\$ – Gareth Jun 13 '12 at 16:34
  • 2
    \$\begingroup\$ @Gareth I too like the competitive nature of this idea. I'm looking forward to a question with this plan in mind! \$\endgroup\$ – Gaffi Jun 13 '12 at 19:31
  • 1
    \$\begingroup\$ I think it would be better to split this into a "cops" post and a "robbers" post. \$\endgroup\$ – wizzwizz4 Feb 16 '17 at 9:46
  • 1
    \$\begingroup\$ @wizzwizz4 Wow, this is another blast from the past. I think this pre-dates the cops-and-robbers tag. I always seem to be ahead of my time. :-) \$\endgroup\$ – Gareth Feb 16 '17 at 9:49
  • 1
    \$\begingroup\$ Can we delete this because the sandbox lags so much and this hasn't been touched in 5 years? \$\endgroup\$ – programmer5000 Apr 13 '17 at 17:35

Countability of Sets of Finite Sets

The aim of this challenge is to code-golf a program which returns an iterator that will iterate over all possible non-empty finite sets of positive integers.

So if running long enough, this iterator should eventually touch on {1}, {2, 5}, {3, 6, 112} (ie none of these should occur "at infinity")

You may choose the order in which you iterate over these sets, but the order must satisfy the following requirement:

Under a particular ordering, if S is the i'th set to be returned by the iterator, then we shall call i the index of set S.

Let a restriction (k,T) be an assertion about a set S that says S has size k and T is a subset of S.

For a given restriction (k,T) and iterator IT, let the restricted iterator be the iterator which takes sets returned by IT and filters out sets that don't satisfy the assertion, iterating only over the ones that do. In other words, if IT iterates over the sequence of all sets, the restricted iterator iterates over the subsequence satisfying (k,T). Now if S is the n'th set returned by the restricted iterator, then we'll call n the restricted index of S with respect to (k,T)

Your ordering must satisfy the property that for any restriction there exists a polynomial P(x) such that for any set satisfying the restriction (with index i and restricted index n), i < P(n)

Note that the following ordering is not acceptable:

{1} {2} {1, 2} {3} {1, 3} {2, 3} {1, 2, 3} {4} {1, 4} {2, 4}...

This is the sequence that comes from counting 1, 2, 3, 4, 5, 6... and listing the set bits in the binary representation of each number.

This is because the restriction (1, {}) satisfies only the sets {1}, {2}, {3}, {4}... whose index i as a function of their restricted index is i=2^(n-1) which is not bounded by any polynomial

Sandbox Questions

The reason for the strange requirement at the end is to disqualify any variants on the most natural ordering which simply counts upwards from 1 and enumerates the set bits in each number. In this ordering, the n'th set of length-one occurs at index 2^n which is non-polynomial.

I posted this problem originally, but didn't think of the obvious solution and so I left out the final restriction. I'd like to re-post it with the extra restriction. But first I'd like to know what people think. Is there a better way I can word that restriction or a more natural restriction I could impose instead?

  • 1
    \$\begingroup\$ I don't understand the extra restriction, so I can't suggest a rewording, but I can say that it needs one. (In particular: what is k? And what function does T serve? Is it really a parameter of the property?) \$\endgroup\$ – Peter Taylor Jun 18 '12 at 8:25
  • 1
    \$\begingroup\$ I don't understand it either. Maybe a sample of an ordering, satisfying the requirement, and another one, violating it, would help. \$\endgroup\$ – user unknown Jun 18 '12 at 15:31
  • 1
    \$\begingroup\$ I understand the restriction now, although I haven't worked through the full implications. Does allowing T to be non-empty make a significant difference at all? \$\endgroup\$ – Peter Taylor Jun 19 '12 at 6:52
  • 1
    \$\begingroup\$ I don't know. It may not. I guess the size part is the important part. I was just thinking that the ordering should be such that you run into all kinds of sets frequently. \$\endgroup\$ – dspyz Jun 20 '12 at 7:17
  • 1
    \$\begingroup\$ Can we delete this because the sandbox lags so much and this hasn't been touched in 5 years? \$\endgroup\$ – programmer5000 Apr 13 '17 at 17:36

Bad Voice Recognition Calculator


Let's say you've decided to operate your computer using voice recognition software, but unfortunately you did a horrible job researching the various products out there and chose a package that does not recognize numbers as numerals, only words. (i.e. "one" (spoken) == "one" (typed), not "1".) Rather than spend more money to get another option, you decide to make do. Now you want to use the computer's calculator, but this poses a problem, since your machine doesn't know how to add "one plus one".


Implement a basic calculator that will read in a string of the written-out equation, perform the correct calculations, then return the result in its text form. Your code should be as short as possible; this is code golf.


  • Input/output will be using your preferred method (STDIN, ARGV, etc.).
  • Your calculator must be able to handle input and output within the billions (non-inclusive) -1,000,000,000 < i < 1,000,000,000, but you may expand to more if you wish.
  • Decimal values and/or parts must be accepted (0 < i < 1) up to 3 places/digits.
    • When calculating answers, proper rounding must be used, so "three point one four one five nine two six" must be returned as "three point one four two".
  • Basic calculator functions required:
    • "Add"/"Plus"/"Sum"/"And" (+)
    • "Subtract"/"Minus"/"Remove" (-)
    • "Multiply"/"Times" (*)
    • "Divide"/"Divided"/"Divide by"/"Divided by" (/)
    • "Raise"/"Exponent"/"Power"/"To the power of" (^)
    • "<Base>Root"/"<Base>Radical" (√)
    • "Point"/"Decimal" (.)
    • "Pi" (π)
  • All strings in the list above must be accounted for in your code, capitalization does not matter.
  • Numbers may be presented as their full value ("one thousand") or by digit (one zero zero zero).
  • Negative numbers may be assigned using "Minus" or "Negative".
    • The string "Minus" bust be accounted for as an operator and identifier. (see example)
  • "And" is only acceptable as an operator, not as part of a named number.
    • "one hundred and one"
    • "one hundred one"
  • "a" or the absence of a number does not equate to any number; all numbers will be explicitly accounted for in the program input.
    • "a hundred" does not equate to "one hundred" and is not a valid input.
  • No more than 2 terms will be used.
    • "one plus one minus one" will not be implemented.
  • If an invalid input is supplied, your function/program should handle the error and exit gracefully with an error description.

Example I/O:

  • "one add one" --> "two"
  • "five thousand thirty four subtract ten thousand six hundred" --> "negative five thousand five hundred sixty six"
    • Alternatively: "five zero three four subtract one zero six zero zero"
  • "three root twenty seven" --> "three"
  • "ten minus minus ten" --> "twenty"
    • Alternatively: "ten subtract negative ten"

Sandbox Questions:

  1. Is this too basic/complicated? (I'm assuming some languages will handle this much more simply than the method I have in my head...)
  2. Does the title fit?
  3. Are there any constraints that should be added/lifted?
  4. Are any more examples needed for clarification?

Thanks for your input, guys!

  • \$\begingroup\$ Not everyone says numbers the same way. Does the parser have to treat the following as equivalent? "negative one hundred five", "minus one hundred five", "negative one hundred and five", "minus one hundred and five", "negative a hundred five", "negative a hundred and five", ...? \$\endgroup\$ – Peter Taylor Jun 15 '12 at 15:12
  • \$\begingroup\$ @PeterTaylor I had had a similar thought re: operators. ("plus" versus "add", etc.) I think it would be more interesting to account for all, but given the wide variety of possible inputs, it may generally be better to limit the options to a specifically defined set (which I have yet to define). \$\endgroup\$ – Gaffi Jun 15 '12 at 15:18
  • \$\begingroup\$ @PeterTaylor I've added some of these details. Please let me know if there's anything unclear about them. \$\endgroup\$ – Gaffi Jun 15 '12 at 16:10
  • \$\begingroup\$ I don't spot any ambiguities in the parser. There is still an ambiguity relating to decimals, though. What precision should be used? Also, I notice now that there's no winning condition. Is this intended to be code-golf? (Ugh - tons of strings which will have to be hard-coded in most languages. I expect Perl has a suitable parser already in CPAN, though...) \$\endgroup\$ – Peter Taylor Jun 19 '12 at 9:03
  • \$\begingroup\$ @PeterTaylor I don't know where I went... I've updated the spec. re: decimal places and objective. \$\endgroup\$ – Gaffi Jun 29 '12 at 13:24
  • 1
    \$\begingroup\$ @PeterTaylor metacpan.org/pod/Lingua::EN::Words2Nums \$\endgroup\$ – msh210 Apr 27 '16 at 20:37
  • \$\begingroup\$ Can we delete this because the sandbox lags so much and this hasn't been touched in 5 years? \$\endgroup\$ – programmer5000 Apr 13 '17 at 17:36

The One with Two Parts

The aim of this challenge is to create a pair of functions which scramble and unscramble any given piece of text.

Part 1

In part one you post your scrambling function, along with the length in characters and language of your unscrambling function (but NOT its code). The length of the scrambler does not affect your score so you needn't golf it unless you want to. The two functions may be written in different languages if you wish.


The scrambling function should take one argument only - a string containing the input text - and return a string containing the scrambled text. The unscrambling function should also take only one argument - the scrambled text - and return the original text. The input text will be limited to characters in the ASCII set range from 0 to 127.

Part 2

In part two you try to beat your opponents' scores for their unscrambling functions. You MUST use the language they specify for their unscrambler in part one. Please give just one answer to this question containing all your unscrambling functions making it clear which question in part one each function unscrambles (maybe each answer in part one should give its scrambler a name for identification?).

Once the closing date (TBA) has passed all participants should post their unscrambling functions in their answer to part one to prove the length, language and functionality of their function.

Scoring The participants score will be calculated as follows: (unscrambler length from part one) - (shortest unscrambler length from part two). The participant with the lowest score wins and will have their answers accepted on both parts of the challenge. To be eligible to win a participant must have taken part in both parts of the question.


In part 1:

  • Bob posts a Python answer and says his unscrambler is a 165 character Python function.
  • Fred posts a GolfScript answer and says his unscrambler is a 59 character GolfScript function.
  • Joe posts a JavaScript answer and says his unscrambler is a 180 character PHP function.
  • Jim posts a Ruby answer and says his unscrambler is 163 character Ruby function.

In part 2:

  • Bob posts an 82 character GolfScript function to unscramble Fred's scrambled text. He also posts a 175 character PHP function to unscramble Joe's scrambled text.
  • Fred posts a 181 character PHP function to unscramble Joe's scrambled text.
  • Joe posts a 150 character Python function to unscramble Bob's scrambled text.
  • Jim posts a 156 character Python function to unscramble Bob's scrambled text. He also posts a 91 character GolfScript function to unscramble Fred's scrambled text.

The scores:

  • Bob scores 165 - 150 = 15
  • Fred scores 59 - 82 = -23
  • Joe scores 180 - 175 = 5
  • Jim scores 163 - 0 = 163

so Fred wins.


I suggest that the closing date be two weeks after the challenge begins, and that unscramblers be posted to part one within 48 hours of closing date in order to be eligible.

  • \$\begingroup\$ Are there any rules regarding scrambling? i.e. is "Stockholm"->"Stockhoml" a valid scramble? (it may not matter, but I'm curious. And to be clear, the scoring is the difference between your opponent's unscrambler length and your own for the same language? \$\endgroup\$ – Gaffi Jul 16 '12 at 16:39
  • \$\begingroup\$ @Gaffi No, you scramble however you want. If you want to just output the text as given that's ok, but you probably won't win with that strategy. The aim is to do it in a way that is easy for you to unscramble but difficult for all the others. That way your score will be smaller. Yes, the score is the difference between your score and the score of the best of your opponents' attempts. I'll add an example to make that bit clearer I think. \$\endgroup\$ – Gareth Jul 16 '12 at 21:27
  • \$\begingroup\$ I think this gives an advantage to people who use (relatively) obscure languages. If the scrambler is written in J and the descrambler in GolfScript then only people who know both can realistically attempt a descrambler. (NB the rules don't say how the score works if no-one attempts a particular unscrambler). \$\endgroup\$ – Peter Taylor Jul 17 '12 at 6:59
  • \$\begingroup\$ I did consider saying that programs that had no attempts at beating them were not eligible to win, but then I thought that if they were scored as though the shortest attempt to beat them was 0 then they wouldn't have much of an advantage. I'll add that into the example scoring. What do you think? I want to encourage answers that are clever or well obfuscated rather than written in Malbolge or something like that. \$\endgroup\$ – Gareth Jul 17 '12 at 7:28
  • 1
    \$\begingroup\$ Does it mean that since no one attempts to solve Jim's Ruby challenge his chances are minimal that he'll win? That would discourage complicated scramblers or difficult languages. \$\endgroup\$ – Howard Jul 17 '12 at 17:12
  • \$\begingroup\$ @Howard As it stands, yes that's how it would work. The alternative, as Peter Taylor points out, is that people using obscure languages have an advantage. I'm not sure how else I might score unscramblers that no-one has attempted to beat. Maybe give them a score of 0? Please, if you or anyone else has any suggestions for making the challenge as inclusive as possible, let me know. \$\endgroup\$ – Gareth Jul 17 '12 at 17:51
  • \$\begingroup\$ Can we delete this because the sandbox lags so much and this hasn't been touched in 5 years? \$\endgroup\$ – programmer5000 Apr 13 '17 at 17:37

Huffman Decoding

Write a programm which takes two strings as input and prints a text.

The first argument is a Huffman Tree, serialized in the following format:

  • every ascii character except ~ is always a leaf, if ~ is the first characater it is also a leaf.
  • <tree0><tree1>~ is a tree where <tree0> is the left subtree and <tree1> is the right subtree.

Example: ab~cde~~~ generates this tree:

┌┴┐ ┌┴─┐
a b c ┌┴┐
      d e

where a would have the key 00, b 01, c 10, d 110 and e the key 111.

The second argument is a text that has been compressed with with the Huffman code that is defined by the first parameter. This bit-string can contain any bit sequence (also null-bytes and non-printable characters) and is not byte aligned, therefore it has been encoded with a variation of the standard Base64 encoding:

  • the characters used for the encoding are the standard base64 characters: ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/
  • the bitstring is broken up into 6-bit chunks and mapped to this characters
  • if the last chunk is smaller than 6 bits, a character with this prefix is used, and padding characters are added to the string:
  • - : the last chunk was five bits long
  • = : the last chunk was four bits long
  • =- : the last chunk was three bits long
  • == : the last chunk was two bits long
  • ==- : the last chunk was one bit long


bits:       1 1 1 1 0 1 1 0 1 0 0 1 1 1 0 1 0 1 0 0 0 1 1 0 1
chunks:    |1 1 1 1 0 1|1 0 1 0 0 1|1 1 0 1 0 1|0 0 0 1 1 0|1[0 0 0 0 0]|
characters:       9           p           1           G           g
base64:     9p1Gg==-

Your programm has to decode the text encoded in the second parameter and print it to stdout.

You have to provide your source code encoded in the way described above. The length of your encoded source code + the length of your serialized huffman tree will be the winning criterion.

TODO: example input

  • \$\begingroup\$ It would be helpful to explicitly state the 64 characters used in the encoding. I presume they're A-Za-z0-9+/ but (especially if you're expecting people to implement that part explicitly) it's best to make the problem self-contained. \$\endgroup\$ – Peter Taylor Oct 8 '12 at 16:23
  • \$\begingroup\$ Hello! This looks like a good but abandoned meta post, would you be willing to offer it for adoption? (If you want to, you can still post to main.) \$\endgroup\$ – programmer5000 Jun 9 '17 at 15:30

Compile BF to TM

Your task is to write a compiler accepting a Brainfuck program (previous challenge: Interpret Brainfuck, wikipedia: Brainfuck) as input and outputting a Turing Machine which produces identical output when supplied with the same (correct) input.

You may select the output format from among the various formats accepted by the answers to Turing Machine Simulator.

The following links may also be useful.
An introduction to programming in BF
BF is Turing-complete
Programming a Turing Machine
Programming Praxis: Turing Machine Simulator

Equivalently, you may write a Brainfuck interpreter in TM, or any partial compilation/interpretation which results in a TM program as described above.

If we consider squares of the TM tape to represent bits (blank=0, mark=1) of the BF memory, then eight squares represent a cell. Each BF instruction translates to a minimum of 8 states of the Turing Machine.

'>' "advance" (++ptr) could be implemented by eight states (sixteen transitions):

adv8 _ adv7 R _
adv8 1 adv7 R 1
adv7 _ adv6 R _
adv7 1 adv6 R 1
adv6 _ adv5 R _
adv6 1 adv5 R 1
adv5 _ adv4 R _
adv5 1 adv4 R 1
adv4 _ adv3 R _
adv4 1 adv3 R 1
adv3 _ adv2 R _
adv3 1 adv2 R 1
adv2 _ adv1 R _
adv2 1 adv1 R 1
adv1 _ link R _
adv1 1 link R 1

where 'link' represents the first state of the following instruction.

'<' "rewind" (--ptr) can be implemented similarly by making leftward movements and rewriting the same symbol just read.

'+' "increment" (++*ptr) can be implemented by a ripple-carry from the Least Significant Bit to the Most Significant Bit, borrowing "rewind" states to back-up to normal position. If the LSB is on the left, it would look something like this:

inc8 _ link N 1
inc8 1 inc7 R _
inc7 _ rew1 N 1
inc7 1 inc6 R _
inc6 _ rew2 N 1
inc6 1 inc5 R _
inc5 _ rew3 N 1
inc5 1 inc4 R _
inc4 _ rew4 N 1
inc4 1 inc3 R _
inc3 _ rew5 N 1
inc3 1 inc2 R _
inc2 _ rew6 N 1
inc2 1 inc1 R _
inc1 _ rew7 N 1
inc1 1 overflow N 1

where overflow is a HALT state.

For I/O, the simplest way I can think is to place all input on the tape after the memory area, and expand the alphabet to include a symbol indicating the dividing line between the memory portion and the input portion of the tape. In fact, by expanding the cell size to nine squares, this symbol can serve as an input pointer, advancing as the input is consumed. (So "advance" and "rewind" now need 9 states each.) And another new symbol is written in front of the current memory cell to serve as the memory pointer. Inputting a byte therefore consists of schleping each bit over the entire space between the two tape positions with something like this:

input _ set-memptr L _
input 1 set-memptr L 1
set-memptr _ find-inptr R *
find-inptr _ find-inptr R _
find-inptr 1 find-inptr R 1
find-inptr $ schlep-bit R $
schlep-bit _ schlep-blank L _
schlep-bit 1 schlep-one L 1
schlep-blank $ schlep-blank L $
schlep-blank _ schlep-blank L _
schlep-blank 1 schlep-blank L 1
schlep-blank * deposit-blank R *
schlep-one $ schlep-one L $
schlep-one _ schlep-one L _
schlep-one 1 schlep-one L 1
schlep-one * deposit-one R *
deposit-blank _ etc R _
deposit-blank 1 etc R _
deposit-one _ etc R 1
deposit-one 1 etc R 1

where "etc" represents going to get the next bit in similar fashion.

To perform a loop (all BF loops are "while" loops, so the exit control is at the beginning and the end has a simple goto back to the beginning), we need first to check is the current cell is zero,

zero8 _ zero7 R _
zero8 1 body R 1
zero7 _ zero6 R _
zero7 1 left1 L 1
zero6 _ zero5 R _
zero6 1 left2 L 1
zero5 _ zero4 R _
zero5 1 left3 L 1
zero4 _ zero3 R _
zero4 1 left4 L 1
zero3 _ zero2 R _
zero3 1 left5 L 1
zero2 _ zero1 R _
zero2 1 left6 L 1
zero1 _ exit-loop R _
zero1 1 left7 L 1
left7 _ left6 L _
left7 1 left6 L 1
left6 _ left5 L _
left6 1 left5 L 1
left5 _ left4 L _
left5 1 left4 L 1
left4 _ left3 L _
left4 1 left3 L 1
left4 _ left3 L _
left4 1 left3 L 1
left3 _ left2 L _
left3 1 left2 L 1
left2 _ left1 L _
left2 1 left1 L 1
left2 _ loop-body L _
left2 1 loop-body L 1
loop-body-final _ zero8 N _
loop-body-final 1 zero8 N 1

So assuming the machine starts at tape-location 0, and the input is on the tape starting at 0 and going to the right, the "startup code" for this arrangement would be

startup _ place$ L _
startup 1 place$ L 1
place$ _ left270000 L $
left270000 _ left269999 L _

Jeez! The output is going to be HUGE! It might be better to treat the BF memory as negative-indexed and reverse all the _L_s and _R_s in 'advance', 'rewind', 'increment', and 'decrement'.


Bonuses for optimizations? If I can implement this myself and provide a complete example output, The bonus could be "subtract the difference between your program's output for the example input with the example output". So eliminating states would be far more valuable than shrinking the code. One could possibly achieve a negative score!

Edit: Actually I think this is unreasonable unless the Turing Machine is augmented with non-reading (movement-only or epsilon) transitions. Duplicating every letter of the alphabet just to move over one square is just ridiculously painful. That means this challenge won't link-up nicely with the other one. :(

What about, instead of implementing the compiler, just devise a translation scheme (as above) that leads to a smaller output for a trivial sample program (based on calculating, rather than coding)? "Back of the envelope" compiler.

  • \$\begingroup\$ "How much detail on BF do I need to supply? Can I simply reference the BF question?" A link to almost any site that describes the language will do. \$\endgroup\$ – dmckee Nov 5 '12 at 16:52
  • \$\begingroup\$ Winning condition? \$\endgroup\$ – Peter Taylor Nov 6 '12 at 13:43
  • \$\begingroup\$ "Longest prefix containing syntactically-correct Malbolge!" :) ... I'd say have none at all. Perhaps the questioner should be required to accept their own example answer? \$\endgroup\$ – luser droog Nov 6 '12 at 18:08
  • \$\begingroup\$ @PeterTaylor Apologies for my last comment. I thought we were on my other answer about the [fun] tag. . . . This one would be a golf: shortest code by character count. But I think a clever system of bonuses could make it interesting. \$\endgroup\$ – luser droog Nov 7 '12 at 10:06
  • \$\begingroup\$ The "Equivalently, you may write a Brainfuck interpreter in TM" option doesn't play very well with being a code golf - how are you going to count the length of the TM? \$\endgroup\$ – Peter Taylor Nov 7 '12 at 11:15
  • \$\begingroup\$ @PeterTaylor Since the TM question specified 5-tuples, I think it's sufficient to count the tuples (== transitions). You can reduce states by increasing the alphabet (or vice versa), but the transitions would remain constant, I think. \$\endgroup\$ – luser droog Nov 8 '12 at 5:25
  • \$\begingroup\$ Can we delete this because the sandbox lags so much and this hasn't been touched in 5 years? \$\endgroup\$ – programmer5000 Apr 13 '17 at 17:42
  • \$\begingroup\$ I'd like to adopt (work on and post) this challenge if you don't want to. Would I be able to? If you do not respond to this message within two weeks, by community guidelines, I am allowed to take it over. \$\endgroup\$ – MD XF Aug 18 '17 at 3:23
  • \$\begingroup\$ Yes, please. If you can do something with it, strike while the iron is hot. \$\endgroup\$ – luser droog Aug 18 '17 at 4:19

Graphical Output -- Esoteric Artifacts -- The Glass Bead Game

Draw the Cabalistic Tree of Life

Simply described, the Tree of Life is an undirected network of nodes representing the conduit between matter and higher forms of spiritual energy. It has an upper face arranged in a hexagon, and a lower fact built from equilateral triangles adjacent to the lower two edges of the upper face. Don't label the paths, paths may overlap however you wish, may be single (thick) lines, even. Code Golf. Bonus -100 for labels on the Sephiroth (nodes); Bonus -150 for Hebrew labels.

Tree of Life after Kirtcher

Draw a Mandala for each Natural Number

Draw a circle with interesting visual patterns using the input N [ 1 .. \inf ) to determine the number of points around the circle to anchor figures whose shape is also modified by the input N. Actually, 12 seems like a good max: they're pretty much a blur after that no matter what.

Eg. http://code.google.com/p/xpost/downloads/detail?name=ve6a.ps
//lotsoflines n = 1 ..12

Mandalas 1 - 12

(doesn't need to be this elaborate, This is >600 lines of showing-off.).

. . . need good images for these . . .

Draw the Ptolemeic System of the Universe

All the stuff I could find is animated already. Maybe this one's done-to-death. :(

Update: Found good stuff on Alchemy. The "Keplar Platonic" model could be fun (3D and all). This one looks good, too. And this.

Draw the Pythagorean Monochord

aka pre-classical nomogram. I misplaced my Pythagoras books, I know I've got a picture somewhere.

This is the one I was thinking of.

But I think this one's even cooler

Draw the I-Ching Hexagrams in King Wen Sequence.

I suppose I need to implement this first to avoid copyright issues! :)

  • \$\begingroup\$ The I-Ching one would have to be in standard order to be remotely interesting, and then becomes as much about kolmogorov-complexity as graphical-output \$\endgroup\$ – Peter Taylor Nov 22 '12 at 21:24
  • \$\begingroup\$ For the others: images, please! \$\endgroup\$ – Peter Taylor Nov 22 '12 at 21:25
  • \$\begingroup\$ I've emailed the owner of the Alchemy pages asking for permission to use his copyrighted images. Awaiting response. \$\endgroup\$ – luser droog Jan 28 '13 at 8:25
  • \$\begingroup\$ Can we delete this because the sandbox lags so much and this hasn't been touched in 5 years? \$\endgroup\$ – programmer5000 Apr 13 '17 at 17:42

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