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What is the Sandbox?

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.

To post to the Sandbox, scroll to the bottom of this page or click on the "Add Proposal" link below, and click "Answer This Question". Click "OK" when it asks if you really want to add another answer. Write your challenge just as you would when actually posting it. You may also add some notes about specific things you would like to clarify before posting it. Other users will help you improve your challenge by rating and discussing it. When you think your challenge is ready for the public, go ahead and post it, replace the post here with a link to the challenge and delete it.

See the Sandbox FAQ for more information on how to use the Sandbox.

The Sandbox works best if you sort posts by "active".

Add Proposal

Search the Sandbox

Browse your pending proposals

Get the Sandbox Viewer to view the sandbox more easily

To add an inline tag to a proposal use shortcut link syntax with a prefix: [tag:king-of-the-hill]

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2922 Answers 2922

1
31 32
33
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1
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A meander is a self-avoiding closed curve which intersects a line a number of times.

Your task is, given a self-avoiding walk on a lattice/grid, produce a meander a la the following:

Input

{{{3, 4}}, {1, 2}, {2, 6}, {6, 7}, {7, 3}, {3, 4}, {4, 8}, {8, 12}, {12, 11}, {11, 10}, {10, 9}, {9, 5}, {5, 1}}

Output

enter image description here

or similar.

Test cases:

Inputs

a={{{3, 5}}, {{1, 2}, {2, 3}, {3, 8}, {8, 9}, {9, 4}, {4, 5}, {5, 10}, {10, 15}, {15, 14}, {14, 13}, {13, 8}, {8, 7}, {7, 12}, {12, 11}, {11, 6}, {6, 1}}}
b={{{3, 6}}, {{1, 2}, {2, 8}, {8, 9}, {9, 3}, {3, 4}, {4, 10}, {10, 11}, {11, 5}, {5, 6}, {6, 12}, {12, 18}, {18, 17}, {17, 16}, {16, 10}, {10, 9}, {9, 15}, {15, 14}, {14, 13}, {13, 7}, {7, 1}}

Output

In the above examples, the numbers correspond to a grid, bottom to top, left to right, so 1 is bottom-left, and 18 on a 3*6 grid is top-right. The orientation of your grid doesn't have to follow this order: it can have any desired orientation.

You can assume dimensions of the grid are given at the begining of the input, as per the obove examples.

Feel free to use either pre-existing images - eg

enter image description here enter image description here enter image description here enter image description here enter image description here enter image description here enter image description here enter image description here

or generate your own. This is Code Golf, so the shortest answer in bytes wins.

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  • 1
    \$\begingroup\$ I'm still not clear how the points relate the the final image. For the pre-existing images, can we use them at no bytes cost? Is the code for loading them free? \$\endgroup\$ – xnor Aug 4 '16 at 10:44
  • \$\begingroup\$ @xnor I think you are right - it is not clear as it stands - think I will leave it on the back-burner for the moment. \$\endgroup\$ – martin Aug 4 '16 at 12:31
1
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THIS A QUESTION IN PROGRESS

ASCII Art converter

see ASCII Art on Esolangs

Your task is to take input of a brainf*** program and output its equivalent ASCII art program. Your challenge: You may not use the following symbols in your program: \ / - | _ # Standard loopholes not allowed...

This is a so shortest answer in bytes wins

OR

ACII Art Interpreter

Your task is to create an interpreter for the ASCII art language. ASCII Art is a variant of brainf*** where characters are instead ASCII art figures 5 lines tall.

< looks like

 /
/
\
 \

> looks like

\
 \
 /
/

+ looks like

  |
  |
-----
  |
  |

- looks like

-----

[ looks like

____
|
|
|
|___

] looks like

____
   |
   |
   |
___|

. looks like

##
##

, looks like

##
##
_|

Characters that are less than 5 characters tall may be placed anywhere within the top line and bottom line of input.

____________________ top line
     \
      \
      /
     /
        <--- gap because this char is only 5 characters tall
_____________________bottom line

There may be any amount of white space between characters. Also characters can be "nested" in each other, as long as they do not touch. EG

____ |  ##
|    |  ##
|  -----_|
|    |
|___ |

is perfectly valid

Your code should not allow improperly formatted ASCII art, and should print to Standard error. For example, the following code should not work

\
 \
  |
  |
  |____

This is a , so the shortest answer in bytes wins!
Additional tags:

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  • \$\begingroup\$ What is the winning criterion (is it codegolf, popularty contest, anything else...), and what is the font to use? \$\endgroup\$ – TuxCrafting Aug 3 '16 at 17:06
  • \$\begingroup\$ @TùxCräftîñg By font, what do you mean - the ASCII art page on esolangs depicts what each and every symbol should look like \$\endgroup\$ – vikarjramun Aug 3 '16 at 17:31
  • \$\begingroup\$ Nevermind, I haven't seen this part \$\endgroup\$ – TuxCrafting Aug 3 '16 at 17:39
  • \$\begingroup\$ Welcome to PPCG and thanks for using the sandbox! Unfortunately, this is basically a dupe of this challenge with a do X without Y bit tacked on, so I don't think this will be received well. I'm not really sure if there is a way to salvage your intent, here, but I recommend trying something different. Best of luck! \$\endgroup\$ – FryAmTheEggman Aug 3 '16 at 17:45
  • 1
    \$\begingroup\$ 1. If at all possible, posts should be self-contained. The Esolangs page you link to might change or disappear. 2. You should specify how the commands should be chained (horizontally, vertically or something else), how they should be aligned, and how much whitespace has to separate them. 3. In my opinion, forbidding those characters doesn't make the challenge more interesting. \$\endgroup\$ – Dennis Aug 3 '16 at 17:49
  • \$\begingroup\$ @FryAmTheEggman Except my challenge is meant to convert only brainf*** code \$\endgroup\$ – vikarjramun Aug 3 '16 at 17:49
  • \$\begingroup\$ I'm afraid that isn't nearly enough to make it not a duplicate, in my opinion. However, Dennis brings up a potentially interesting point, you may be able to salvage this by also requiring that the code be "formatted" a certain way. I also agree with the rest of the advice Dennis gave you, and I think you should address them before deciding on what else to do. \$\endgroup\$ – FryAmTheEggman Aug 3 '16 at 17:52
  • \$\begingroup\$ What if I change it to a ASCII art interpreter \$\endgroup\$ – vikarjramun Aug 3 '16 at 17:57
1
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Your job is to take an input like below:

Hello, world!

π is cool!

and output it as a series of <kbd>.

Every character, including enter and space get their own <kbd> HTML element, like so:

Hello,SPACEworld!NEWLINE

OPT + PSPACEisSPACEcool!

Other characters like space and newline that are invisible and typeable (so no option, command, control, function, escape, delete, arrow keys, etc.) are all uppercase, like SPACE and NEWLINE. OPT is an exception because it is used to create new characters. The code for these characters are:

<kbd>SPACE</kbd> <kbd>NEWLINE</kbd>

Special characters needing to be typed using option use the following format OPT + P instead of π. The following code is used for these:

<kbd><kbd>OPT</kbd> + <kbd>P</kbd></kbd>

The same applies to characters that are typed using OPT + SHIFT + K instead of .

We're assuming this is a QWERTY layout computer.

Here are the available option keys:

Option keys

Any of the orange keys are not allowed in this.

Here are the OPT + SHIFT keys:

Option shift keys

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  • 5
    \$\begingroup\$ +1 for well laid out challenge -1 for being mac specific \$\endgroup\$ – Rohan Jhunjhunwala Aug 9 '16 at 19:33
  • \$\begingroup\$ @RohanJhunjhunwala It's not technically Mac-specific, but rather uses the same shortcut keys to type special characters as a Mac. \$\endgroup\$ – haykam Aug 9 '16 at 19:35
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    \$\begingroup\$ Yeah, Ina all seriousness here have an upvote, It does seem like targetting the opt key may be somewhat confusing for some S̶a̶n̶e̶ pc users. \$\endgroup\$ – Rohan Jhunjhunwala Aug 9 '16 at 19:39
  • 1
    \$\begingroup\$ For each letter you check which of the three character sets it is in then add some fixed strings to it. It doesn't seem to me like there is much interesting stuff to do in there? I'm not sure this adds much to the other keyboard focused challenges that we have. \$\endgroup\$ – FryAmTheEggman Aug 9 '16 at 20:23
  • \$\begingroup\$ Do all of those characters even have Unicode codepoints? \$\endgroup\$ – Peter Taylor Aug 10 '16 at 5:31
1
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Find the Watermark

At the moment, I don't have time to outline this properly. The idea is simple: Find the watermark in an image. The implementation, however, is obviously not simple. Since watermarks can have a variety of characteristics, I'd like to admit a variety of answer styles and make it a . Some ideas for the output format:

  • Return coordinates of the (centre|corner(s)?) of the watermark
  • Return a line in some form (e.g., endpoints or equation) that runs through the watermark
  • Return an image that contains only a mask matching the watermark

Input, obviously, would be an image containing a watermark. Images without watermarks are not valid input; as such, submissions do not need to handle them in any special way.

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    \$\begingroup\$ I fear that this is far too vague, and probably too difficult. \$\endgroup\$ – Joe Aug 21 '16 at 2:10
  • \$\begingroup\$ Maybe a test-battery tag? \$\endgroup\$ – Rohan Jhunjhunwala Aug 21 '16 at 2:19
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    \$\begingroup\$ Yes, seeing the proposed test cases would give a much better idea of whether this is realistic. \$\endgroup\$ – trichoplax Aug 21 '16 at 7:40
  • \$\begingroup\$ I hereby encourage any member of the community to take over this challenge. I have no experience with graphical I/O, and I don't foresee myself gaining any in the near future. I doubt that I can write a reasonable spec; also, I'm just not that interested in it anymore. \$\endgroup\$ – Joe Sep 5 '16 at 20:37
1
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whispering and SHOUTING

Typing in all caps on the internet is often called "shouting". For the sake of this challenge, I'll call typing in all-lowercase "whispering".

The challenge

Write a complete program that can be run in two different ways: whispering and shouting. The "whispering" version of the program must be written in all-lowercase characters, and it should print whisper to STDOUT. The "shouting" version of the program will print SHOUT. The shouting version must be the exact same program as the whispering version, but with all lowercase letters replaced by the uppercase version of the letter. Everything else must be identical.

Rules

  • No standard loopholes
  • This is , so shortest program in bytes wins!
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  • \$\begingroup\$ Is shortest program in bytes? \$\endgroup\$ – Buffer Over Read Aug 21 '16 at 2:46
  • \$\begingroup\$ Yes, I'll clarify that \$\endgroup\$ – Daniel M. Aug 21 '16 at 2:46
  • \$\begingroup\$ Though I'm not too sure if I want to keep the restriction of not containing the words because it feels kind of arbitrary and that isn't the point of the challenge \$\endgroup\$ – Daniel M. Aug 21 '16 at 3:52
  • \$\begingroup\$ It may be a "Do X without Y" question, which could be bad if not done carefully. \$\endgroup\$ – Buffer Over Read Aug 21 '16 at 3:53
  • \$\begingroup\$ @ColdGolf The difference between this and a do X without Y is that this challenge focuses on actually doing the X (a non-trivial task) instead of focusing on not using Y. Still, I think I'll get rid of the restriction because a) I'd like to focus more on the X and b) the restriction is trivial to circumvent (simply use concatenation) \$\endgroup\$ – Daniel M. Aug 21 '16 at 3:59
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    \$\begingroup\$ What about characters that don't have a case? Or characters that have more than two cases? Is the program restricted to ASCII? \$\endgroup\$ – FryAmTheEggman Aug 21 '16 at 4:13
  • \$\begingroup\$ @FryAmTheEggman characters without a case don't have to change. What character has more than 2 cases? And it's whatever encoding the program uses. \$\endgroup\$ – Daniel M. Aug 21 '16 at 11:54
  • \$\begingroup\$ Sigma has three total variants. Not restricting this to ASCII makes it seem rather odd. Couldn't a language totally avoid the problem by writing the program in caseless characters and then checking like A > 65? Additionally, some characters (i.e. small caps) look like they should have lower case variants, but don't AFAIK. What standard of considering things lower case should we follow? Without restricting or clarifying this, I think this is too unclear. \$\endgroup\$ – FryAmTheEggman Aug 21 '16 at 13:31
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Switching lines

Let's say you have a string of text:

Hello, World! Today is a
most glorious day. In fact,
it's another day. Woohoo!

This string has three lines. We can call them lines 1, 2, and 3. (Or, if you prefer zero-indexing, lines 0, 1, and 2. I'll be using one-indexing to describe this challenge.)

Let's also say we have a mapping of line numbers to line numbers, such as 1 => 2, 3 => 1, 2 => 3. We will interpret this mapping as a method of "switching" lines with each other; the first rule switches line 1 with line 2, then line 3 with line 1, then line 2 with line 3. This would make the string look like, with intermediate steps:

Rule: (initial)
1. Hello, World! Today is a
2. most glorious day. In fact,
3. it's another day. Woohoo!

Rule: 1 => 2
2. most glorious day. In fact,
1. Hello, World! Today is a
3. it's another day. Woohoo!

Rule: 3 => 1
2. most glorious day. In fact,
3. it's another day. Woohoo!
1. Hello, World! Today is a

Rule: 2 => 3
3. it's another day. Woohoo!
2. most glorious day. In fact,
1. Hello, World! Today is a

Notice how the rule describes lines to be switched, not merely lines in that index. So each line has a permanent, associated line number.

Any rule such as 1 => 1 is effectively a no-operation.

Objective Given a list of numbers in any convenient format (e.g. an array of pairs of integers, a list like A B\nC D, a list of numbers, etc.) and a non-empty string of text, perform the action described above.


Meta

is it a good idea to do line identity instead of line locations?

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  • \$\begingroup\$ So the requirements are 1) number the lines; 2) apply the permutation which results from composing a series of simple swap permutations, each of which must be interpreted in the light of the previous ones? The lines really seem to be superfluous: the core of the question is the permutations, surely? \$\endgroup\$ – Peter Taylor Aug 27 '16 at 19:13
  • \$\begingroup\$ @PeterTaylor I suppose that's true. It would certainly simplify the questions. \$\endgroup\$ – Conor O'Brien Aug 27 '16 at 19:26
1
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Tweetable Video

This challenge is inspired by the Encode Images into Tweets challenge, extending the idea to now attempt to compress video into a series of "tweet" sized messages where the number of tweets == number frames of the video.

The competition is to compress 450 frames of video into 450 (or less) tweets of 140 charactes ( 114.97 bytes per tweet, total max 51737 bytes).

Original frames as Video, as PNG images [Sandbox note: Higher quality version will be uploaded soon]

Reference solution frames as Video [Sandbox note: Reference solution will be expanded once challenge changes stabilized]

Rules:

These rules are the based from rules in Encode Images into Tweets modified to accommodate multiple frames that will yield the resultant video.

  1. You must write a program that will communicate via std in/out based on the communication protocol defined below, ultimately producing a series of tweets that will, when fed back to your program, produce image frames of the video.
  2. The text created for each 'Tweet' by the program must be at most 140 characters long and must only contain characters whose code points are in the range of 32-126, inclusive.
  3. The source video will be 450 frames of Big Buck Bunny. Frames can be downloaded here
  4. Frames will be width 320 pixels and height 240 pixels @ 24 bit RGB, each channel having 8 bit precision.
  5. Your program should be able to compress other video sources at same resolution.
  6. Your program can use external libraries and files, but cannot require an internet connection or a connection to other computers.
  7. The decoding process cannot access or contain the original images in any way. (Clarification use of corpus images is allowed as long as these images do not contain direct or manipulated original image frames)
  8. Use of video codecs or existing libraries that perform video compression are not allowed. This is to encourage experimentation and originality rather than simply calling libraries. Note that use of static image compressors/ libraries are allowed.
  9. Standard Loopholes are forbidden.

Communication Protocol

  1. All communication is via std in/out.
  2. The controller program will launch your program with no command line arguments.
  3. The controller will either initiate a one of the following sequences commanding to your program and expecting results.

Note the sequences are described below in the following format:

<Comms direction from controller perspective>, <seq number>: <Transmitted Data> - <Information> 

For Encoding of the frames:

Output, 1: ENCODE\n - Indicating that the controller will be sending frames for your program to compress.
Output, 2: <number of frames>\n - String indicating number of frames. i.e. 450
Output, 3: <number of bytes for image data>\n - String indicating number of bytes of the current image data. e.g. 32145
Output, 4: <image data> - sequence of bytes of length defined in output line 3. The is the image data. The image data is a 24 bit image in PNG format
Repeat from output seq number 3 for the number of frames in output seq number 2.
Input, 1: <Tweet>\n - encoded image data. upto 140 characters, whose code points are in the range of 32-126, inclusive. A zero sized tweet will indicate end of all tweets.
Repeat from input line 1 for 1 to up to the number of frames in output seq number 2. Note a zero sized tweet will indicate end of all tweets.
Output, 5: END\n - Indicating that all processing has finished and your program should quit gracefully.

For Decoding of the frames:

Output, 1: DECODE\n - Indicating that the controller will be sending tweets for your program to decompress.
Output, 2: <number of tweets>\n - String indicating number of tweets. i.e. 450
Output, 3: <Tweet>\n - encoded image data. upto 140 characters, whose code points are in the range of 32-126
Input, 1: <number image frames decoded>\n - String indicating number of image frames that have been decoded as a result of the provided tweet. If 0 then no images have been decoded for this tweet.
Input, 2: <number of bytes for image data>\n - String indicating number of bytes of the current image data. e.g. 32145.
Input, 3: <image data> - sequence of bytes of length defined in input line 2. The is the image data. The image data is a 24 bit image in PNG format. 
Repeat from input seq number 2 for the number of frames in input seq number 1.
Repeat from output seq number 3 for the number of tweets in output seq number 2.
Output, 4: END\n - Indicating that all processing has finished and your program should quit gracefully.
  1. Your program will be restart between the encoding and decoding phases.

Scoring

As an attempt to model the human visual system in a simplistic manner, JPEG quality levels are used as an analogue. Each frame will be compressed to a JPEG using quality levels 0.01 to 1.0 in 0.01 increments. The PSNR of these JPEG compressed versions are calculated and added into a data structure. Additionally, each frame will be resized by half and the JPEG encoding and PSNR calculations performed and added to the data structure. The resizing and calculating will repeat until a single pixel is left.

The result of which will be a scoring continuum of visual 'quality' from low (single color frame) to High (near-identical to original).

Thus, scoring will be objective by means of the following formula:

JPEG_QUALITY_LEVEL_PSNR = a pre-computed data multi dimensional structure consisting of the
                          PSNR for incremental JPEG quality levels for each image frame of
                          the video. The entries into this structure for each frame is such
                          that higher indecies are deemed to be of more similar to the
                          original.

Score = SUM of (index of closest matching entry in JPEG_QUALITY_LEVEL_PSNR for given
                original frame and given PSNR of decoded frame)

Controller

[Sandbox note: Controller is to be created]

Refrence Solution

[Sandbox note: Reference is to be created once question stabilizes]

Sandbox Questions

Ok, so this is my first question ever posed to codegolf and I am very keen to get feedback on how to better present the challenge.

Some areas where I would like specific feed back is the objective scoring mechanism... i purposely avoided direct PSNR as the score as it is very limited for scoring video quality, being biased toward blurry images, however other algorithms are too complex or not defined. So as a compromise I am using JPEG compression as an analogue for the Human Visual System. Effectively matching a given solutions output frame to original frame PSNR to a JPEG compressed, at a given quality level) version's PSNR and using that match's index in sorted JPEG quality order as input for the score.

Is the protocol clear enough? if not what would be a better way to present it?

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  • \$\begingroup\$ "I introduced it so that solutions that take all the frames then perform processing over all the frames would be at a clear advantage over those solutions than work over a much shorter frame period." I'm not seeing it. If I process all of the frames then the first frame will probably use a lot of tweets and the subsequent ones fewer, so I'll be penalised for the first frame. \$\endgroup\$ – Peter Taylor Sep 21 '16 at 9:25
  • \$\begingroup\$ @PeterTaylor Indeed, that is the point i am ?trying? to make, In the fantasy world where video by tweets is a feature desired by users, having to wait until all the tweets are received before playing the video would be very annoying. So this part of the scoring is to give those solutions that return frames quicker in response to provided tweet(s) an advantage. I am thinking that it may be not that "interesting" or "fun" to have this modifier. I think i shall remove it unless some people think it has some worth. \$\endgroup\$ – Moogie Sep 21 '16 at 11:23
  • \$\begingroup\$ The point I was trying to make is that the feature of the scoring system seems to me to penalise the approach which you say it's trying to promote. \$\endgroup\$ – Peter Taylor Sep 21 '16 at 11:28
  • \$\begingroup\$ oh i apologize, i think i misunderstood. Yes, in the example you have given it will penalize that solution, however it would be less penalized than a solution that waited for all tweets, but more penalized than a solution that immediately gives an image frame after each tweet. i.e. the fantasy user would have to wait longer than if the solution produced images after each tweet. Hmm, given the confusion i will remove the modifer as it will be difficult to tune the "negative" effect as to not completely favour immediate frames vs better quality frames. \$\endgroup\$ – Moogie Sep 21 '16 at 11:42
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Interpret MSF-!

Because there aren't enough "Interpret X" challenges.

MiniStringFuck (or MSF-) is a brainfuck derivate made by @ErikTheGolfer, with two commands, operating on one cell:

InstructionAction                                                                               
+               Increment the memory cell. If it reaches 256, wrap to 0.
.                Output the character in the cell.                                      

or a bad-looking table:

Instruction, Action
+, Increment the memory cell. If it reaches 256, wrap to 0.
., Output the character in the cell.

Task

Your task is to, given a string of MSF- code, containing only printable ASCII characters, output what it would print.

The string may have other characters than + and .. Treat them as NOPs

Example

++++++++++++++++++++++++++++++++++++++++++++++++.+.+.+.+.+.+.+.+.+.
++++++++++++++++++++++++++++++++++++++++++++++++.                    Set cell to 48 (0) and output
                                                 +.+.+.+.+.+.+.+.+.  Keep adding and outputting until 57 (9)

Test Cases

+++++++++++++++++++++++++++++++++.+.+. -> !"#
++++++++++++++++++++++++++++++++++++++++++++++++.+.+.+.+.+.+.+.+.+. -> 0123456789
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. -> ABCDEFGHIJKLMNOPQRSTUVWXYZ
ABCDEFGHIJKLMNOPQRSTUVWXYZ -> (no output)
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  • \$\begingroup\$ Will the input string ever contain other characters? If so, should they be treated as NOP/comments? \$\endgroup\$ – Geobits Sep 22 '16 at 14:16
  • \$\begingroup\$ @Geobits Yes and yes. \$\endgroup\$ – acrolith Sep 22 '16 at 15:39
  • 1
    \$\begingroup\$ This is basically "Parse unary numbers", and as such I think it's a duplicate of codegolf.stackexchange.com/q/76756/194 \$\endgroup\$ – Peter Taylor Sep 22 '16 at 16:20
1
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Priority to the right

Your task is to regulate traffic on a crossroads. There are 4 roads coming from north, east, south and west.

The input is a string representing the upcoming traffic on each road. For example, NNNWS indicates there is a total of 5 cars: three at the north, one at the west and one at the south. The order has no importance here, NNNWS is equivalent to WNNSN.

You must output the order in which the cars should go, using the priority to the right rule: cars coming from the south must let cars coming from east go first, east gives way to north, north gives way to west and west gives way to south.

For example, with the input NNNWS, the south car should go first, then the west car, then the 3 north cars. The output should then be SWNNN.

There are some indecidable cases, for example NS or NNWSE : you should then output the string stuck.

Test cases

N => N
NW => WN
NWS => SWN
SNW => SWN
SSSSS => SSSSS
ENNNNES => NNNNEES
NS => stuck
NNWSE => stuck
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1
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golf.ko - Kernel module golf

A Linux-specific challenge.

Implement a Linux kernel module which printks Hello world upon loading, in some compiled language.


Source file, linker scripts and command lines, Makefile content (if any) are all counted towards the byte score.

You may expect kernel version to be 4.1 or 4.4.

The kernel is assumed to be running. It's built, not cleaned source code is assumed to reside in /usr/src/linux. In addition you may expect the system to be Debian and to have working DKMS.

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  • 1
    \$\begingroup\$ Maybe can be a catalog. \$\endgroup\$ – Vi. Sep 30 '16 at 13:18
  • \$\begingroup\$ What does it mean for a kernel module to "print"? \$\endgroup\$ – Peter Taylor Sep 30 '16 at 18:00
  • \$\begingroup\$ Issue behaviour similar to printk kernel API function in C. Output message to logs, to console, to /proc/kmsg. Shall definition what exactly is a printk be included? Obviously user is expected to call the function inside kernel, not re-implement printk. \$\endgroup\$ – Vi. Oct 2 '16 at 18:29
  • 1
    \$\begingroup\$ I see: "printks" just looks like a typo, it isn't really one. That could be clearer if you wrote "printks", and clearer still if you link to a man page or other documentation. But if you're requiring use of that library, you can pretty much rule out answers in languages other than C and maybe Rust (since what other languages will have bindings for it?), and I wouldn't be surprised if there's nothing interesting left to golf and you just get one answer. \$\endgroup\$ – Peter Taylor Oct 3 '16 at 11:49
  • \$\begingroup\$ @PeterTaylor, Maybe just exclude printk requirement and require just some code derived from posted source code to be executed? Or just the endless loop (it should be doable in almost any language, is API-agnostic and is observable)? \$\endgroup\$ – Vi. Oct 3 '16 at 23:32
1
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Random Quine

(something related to languages?)

You are to write N programs in N langauges (at least 2) that satify the following properties:

  1. For each program P, the program P must produce an output O that is equal to a random program Q that you wrote, including P.
  2. No two programs P and Q may be equal.

Let's say you have two programs, ABCD in language Bar and 1234 in language Baz. Then, ABCD must produce each of ABCD and 1234 with nonzero (but not necessarily equal) probability. Similarly, 1234 must output ABCD or 1234 with nonzero chance. Note that the chances do not have to be same for each program.

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  • \$\begingroup\$ Higher N being winning doesn't seem to be viable on it's own as I think this could be done essentially forever. Will it be something like total length of all Ps divided by N? \$\endgroup\$ – FryAmTheEggman Oct 5 '16 at 22:35
  • \$\begingroup\$ 1. On clarity: it's not clear what the requirements are for which programs each P must produce with non-zero probability. All of them? At least two different ones? ("At least one" would satisfy the stated properties, but not the explanation in the example). 2. On boringness: the programs can just be identical apart from an integer or string literal which they ignore when executing and replace at random when outputting. So a generalised quine of half of the random challenges would meet spec. \$\endgroup\$ – Peter Taylor Oct 6 '16 at 7:28
1
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Introduction

The challenge is to determine if two complex lines intersect.

Challenge

Given two lines made up of multiple straight line segments determine if the lines cross at any point.

Input can be in the format of you choice that takes a series of [x,y] coordinates. All coordinates will be integers (positive or negative)

Output will be truthy if the lines cross and falsey if they don't cross.

There will be no coincidental points and no segment of one line will terminate at a point touching the other line (there will be a clean cross of line segments if the case is truthy).

This is code golf so shortest answer wins

Example Input and Output

For the examples formats are given as

Line 1: [[X1,Y1],[X2,Y2]...,[Xn,Yn]] Line 2: [[X1,Y1],[X2,Y2]...,[Xn,Yn]]

Examples

Line 1: [[0,0],[1,1]] Line 2: [[0,1],[1,0]] = TRUE

Line 1: [[2,2],[1,0],[0,2]] Line 2: [[0,1],[1,1]] = TRUE

Line 1: [[1,3],[2,9],[3,6],[4,7],[5,4],[6,1]] Line 2: [[2,6],[3,5],[5,2]] = FALSE

Line 1: [[0,6],[3,8],[5,5],[8,5]] Line 2: [[0,4],[3,7],[5,4],[7,6]] = TRUE

Line 1: [[2,2],[3,2]] Line 2: [[1,1],[10,4]] = FALSE

enter image description here

Please let me know your thoughts, first puzzle.

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  • \$\begingroup\$ What about the case where one of the line segments "touches" another. That is: one of the end points of a line is on the other line. Would that be considered "crossing" or not? \$\endgroup\$ – DarthRubik Oct 6 '16 at 23:49
  • \$\begingroup\$ @DarthRubik tried to clarify, don't need to handle that case. \$\endgroup\$ – gtwebb Oct 6 '16 at 23:55
  • \$\begingroup\$ All of the test cases have x increasing strictly monotonically. Is this guaranteed, or could line segments be vertical or even loop back? If you don't guarantee that input will avoid those situations, please add test cases to cover them. \$\endgroup\$ – Peter Taylor Oct 9 '16 at 16:11
1
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Raytracing/Raycasting

Here is a 256*256 heightmap. Your challenge is to render it, in minecraft-style blocks, using some form of raytracing.

enter image description here

Fundamental Definitions And Clarifications

These are all straightforward and fairly obvious but I'm being explicit so that what follows is (ideally) unambiguous.

  • Let each pixel represent 1x1 metre, for ease of thought.
  • This image is a top-down view. The bottom-left pixel of the image in screen space is at [0,0,0] in world space. The bottom-right pixel of the image in screen space is at [255,0,0] (i.e. the next full tile to the right would be anchored at [256,0,0]). The Z-axis increases away from us in world space so the top-left pixel is at [0,0,255] and the top-right-pixel is at [255,0,255].
  • As you are looking down to the floor at the moment, you have positive height and the vector from your eye to the image points in the direction of [0,-1,0], so the camera which corresponds to the above image has a world-space coordinate of something like [128,300,128].
  • It shouldn't really matter, but let's take the red channel as holding the height. A red channel value of foo puts that pixel at y=foo. The tallest possible pixel would have world coordinate [x,255,z] with 0<=x,z<256.

Aesthetic Definitions

  • Each pixel effectively represents a tower some number of 1x1x1 solid cubes. The edges of these blocks should be rendered sharply at 90-degree angles. If you were to convert this scene to triangles, each normal would be along one of the major axes. You can think of blocks having end-caps on their top (which is the floor, to us), and walls are extruded between neighbouring blocks as required. There are no holes in the rendered surface. You can assume all renderings will be from above (extra implied geometry below the floor doesn't matter).
  • As well as the heightmap, the world contains one camera and one light source. The light casts hard shadows, so every rendered pixel will require two ray casts. Light falloff is inverse-square. You may optionally gamma-correct the result.
  • Pixels on a surface which receive no light should be black. Pixels of rays which do not hit any surface should be magenta: rgb=(255,0,255).

Input Parameters

  • The camera is defined by position P=[px,py,pz], a T=[tx,ty,tz] target point, and a field of view FOV. It renders WIDTH x HEIGHT images such that the target point appears in the centre.
  • The camera is orientated such that it yaws, then pitches, but does not roll.
  • The light is at position L=[lx,ly,lz] and casts light uniformly in all directions.
  • You solution must be posted with reference image rendered with P=[80,256,0], T=[128,50,200], L=[256,300,128], WIDTH=400, HEIGHT=300 and FOV=45 degrees.
  • (As reference images emerge I might tweak these parameters.)

Free Parameters

  • The light can be any colour and brightness you like but the colour and brightness must be inputs to the program.
  • Likewise, the colour/material of the surface may be anything you like (except magenta, which is for revealing holes) but these colour/material parameters must be an adjustable input to the program.
  • Use any lighting/shader model you like.
  • Use fog or other effects if you like. Different submissions are likely to vary considerably in size, so there's room to play a bit.

Criteria

  • You must post code which can be run as-is, with the specified reference parameters and all your free parameters included.
  • You can take the heightmap image as hardcoded in a representation of your choice and this does not count towards your golf score. You must post the code which converts an image to your preferred format. This script should either run using common Linux command-line tools, or over an online service. This script should not assume that heightmaps are square.
  • The output of raw pixel data can be in any format you like (e.g. [[r,g,b],...] BUT you must provide a second script, not counted towards your golf score, which turns your program's raw output into some standard image format such as PNG. This script should either run using common Linux command-line tools, or over an online service.
  • You must post the final image produced by this method, as well as the code which produces the output which produces the image.

In a nutshell, the above specifies that your output is reproducible, with different parameters and heightmap images as desired.

The winner will be chosen a few weeks from now, as the shortest code which conforms to the above aesthetic specifications (e.g. shadows, no holes, etc) and which gives end-to-end reproducible results.

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  • \$\begingroup\$ Maybe include a sample output? \$\endgroup\$ – Steven H. Oct 7 '16 at 18:10
  • \$\begingroup\$ My own attempt at this is part of a larger, more complex project, it'll be a while :-) In the meantime I was curious if others would find a simplified version of the problem a bit more fun. \$\endgroup\$ – spraff Oct 7 '16 at 19:42
  • \$\begingroup\$ Must run, so will expand on this later, if not within 48 hours then ping me. There are some subtleties with respect to offsets (are blocks centred?) The stuff about fog etc is wasted space, because in code-golf no-one will spend bytes on it, so remove it to KISS. I strongly advise before posting to get a test output which two independent programs agree on. \$\endgroup\$ – Peter Taylor Oct 8 '16 at 8:07
  • \$\begingroup\$ 1. The subtlety I promised to expand on: does "The bottom-left pixel of the image in screen space is at [0,0,0] in world space" mean that the pixel corresponds to the voxel whose coordinates range from (0,0,0) to (1,1,1) or the voxel whose coordinates range from (-0.5, -0.5, -0.5) to (0.5, 0.5, 0.5)? 2. Also, what does "The camera is orientated such that it yaws, then pitches, but does not roll" mean? Perhaps it could be better expressed by giving the initial up, forward, right vectors and then saying around which axes it rotates. \$\endgroup\$ – Peter Taylor Oct 9 '16 at 16:09
1
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A simple but fun code golf challenge!

Given positive integer n

create a 2 dimensional matrix where each location is filled with it's xy index (starting from the top left).

For example:

Your grid should look like: input: 2

00 10
01 11

input: 3

00 10 20
01 11 21
02 12 22

Once the grid is created, randomly fill each index. This can be with an 'x' or any other way to denote a spot has been filled

A complete simulation looks like:

input: 3

x x x
x x x
x x x

O O O
O O O
O O O

You can use whatever character you want to fill in each location.

Extra points if you use a GUI and use black squares to fill it in

You should only fill a spot in once so the number of times you fill should be n^2. (So no randomly filling spots until they are all filled you have to check!)

You can refresh the grid however you want. i.e print the grid, make a new line, print again... You can use a timer. However you want to do it to illustrate each step. You only need to refresh when you are filling not when you are populating the grid.

An example simulation looks like this:

input: 2

00 10
01 11

randomed 01

00 10
XX 11

randomed 11

00 10
XX XX

randomed 11
re-roll
randomed 01
re-roll
randomed 00

XX 10
XX XX

randomed 10

XX XX
XX XX

Complete

Do not display your randomed numbers, the output should tell me which were randomed.

Have fun!

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1
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Just like magic


Nowadays, the word "abracadabra" is used mostly in connection with magic tricks. The original purpose of the word had more to do with superstition, and some doctors used it to make lethal diseases go away by writing it in a triangle1, like so:

A B R A C A D A B R A
 A B R A C A D A B R
  A B R A C A D A B
   A B R A C A D A
    A B R A C A D
     A B R A C A
      A B R A C
       A B R A
        A B R
         A B
          A

Your task is to write a program or function that outputs/returns the exact text shown above in as few bytes as possible. The output may contain trailing spaces on each line and/or trailing newlines. This is , so the shortest code in bytes wins.

1. https://en.wikipedia.org/wiki/Abracadabra


Sandbox questions

  • Is it too simple?
  • Is it a duplicate?
  • Any better name ideas?
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  • \$\begingroup\$ "It's magic, you know! Never believe it's not so!" \$\endgroup\$ – Addison Crump Oct 11 '16 at 20:32
  • \$\begingroup\$ @VTCAKAVSMoACE Haha :) though I'm not sure how many people would get the reference. I had to google the lyrics, but the song sounds very familiar. I wonder where I've heard it before... \$\endgroup\$ – ETHproductions Oct 11 '16 at 20:39
  • \$\begingroup\$ Well, it's the same formatting than Number Triangles, but the task is clearly different. I suppose you could also call it "A Kind of Magic", although the Queen/Highlander reference might be a bit far-fetched. \$\endgroup\$ – Arnauld Oct 11 '16 at 23:04
  • \$\begingroup\$ The closest I can think of as a dupe is codegolf.stackexchange.com/q/65300/8478, but it seems likely that it's shorter to generate each line from the previous instead of generating a string of all prefixes first and the laying it out in a triangle. \$\endgroup\$ – Martin Ender Oct 12 '16 at 12:38
1
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Ungolf batch

This question wants you to golf batch programms. In Batch you can use

set x=averylongbatchcommand
%x% arg1

which expands to

set x=averylongbatchcommand
averylongbatchcommand arg1

Your task is it to expand these statements.
As you can also use set for arithmetic purposes like this:

set x = 0
set /a x= %x%+1

you should ignore the statements where the pattern with set /a is applied.
There will never be something like

set s=SET
%s% s=%s% a

where the variable is assigned using itself as command. But you have to handle things like

b:
set a =echo
%a% Hello World!
set a=goto
%a% b

Scoring

This is so the answer with the fewest bytes wins.

Testcases

set s=set
%s% e=echo
%e% I will have to use this exact thing very often because
%e% it absolutely wouldn't be shorter if i just left out these set statements

Expands to:

set s=set
set e=echo
echo I will have to use this exact thing very often because
echo it absolutely wouldn't be shorter if i just left out these set statements

set s=set
%s% i=0
set g=goto
:a
if %i%==15 (
%g% e
)
%s% /a i=%i%+1
%g% a
:e

Expands to:

set s=set
set i=0
:a
if %i%==15(
set e
)
set /a i=%i%+1
goto a
e:

set s=set
%s% s=%s% a=

Mustn't be supported.

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  • \$\begingroup\$ Too bad the question mentioned has no answers... \$\endgroup\$ – Conor O'Brien Oct 18 '16 at 0:44
  • \$\begingroup\$ I will probably post It tomorrow, if there isn't any critic. \$\endgroup\$ – Roman Gräf Oct 18 '16 at 12:46
1
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Convert Birkana to Hexademical

Introduction

Birkana is a not-very-well-known notation for hexadecimal using rune-like symbols. The general structure of a Birkana rune is like this:

|\     <-- 0x1
|/     <-- 0x2
|\     <-- 0x4
|/     <-- 0x8

The slash or backslash is present if its base number (0x1, 0x2, 0x4, or 0x8) is present in the number, or not otherwise. The pipe is always at the left-hand side.

For example, here's the Birkana rune for 0xD (= 0x1 + 0x4 + 0x8):

|\
|
|\
|/

Challenge

Given a Birkana rune as input, write a program or function to output the corresponding hexadecimal digit.

You may choose to output either lowercase (a-f) or uppercase (A-F) hex digits, but they cannot be mixed.

You only need to support the 16 hexadecimal digits and their corresponding Birkana runes.

Test cases

Input
Output

|
|
|
|
0

|\
|
|
|
1

|
|/
|
|
2

|\
|/
|
|
3

|
|
|\
|
4

|\
|
|\
|
5

|
|/
|\
|
6

|\
|/
|\
|
7

|
|
|
|/
8

|\
|
|
|/
9

|
|/
|
|/
A

|\
|/
|
|/
B

|
|
|\
|/
C

|\
|
|\
|/
D

|
|/
|\
|/
E

|\
|/
|\
|/
F

Scoring

This is , so the shortest answer (in bytes) wins.

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  • \$\begingroup\$ Is this just binary displayed vertically using space/nothing for zero and a slash for a one? I guess the fact that the slashes alternate could just be ignored, treating each position as either empty or full, which would still give the correct output? If so, is it acceptable to output a hex digit for invalid inputs? This is likely to make a difference to the approaches used. \$\endgroup\$ – trichoplax Oct 18 '16 at 12:03
1
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Find the least squares regression line

Background

I'm taking AP stats now, so I figured I'd bring the joy to you all here.

The form of an LSRL (least squares regression line) is ŷ = a + bx.

Input

Your job is to find the least squares regression line for two data sets (lists), X and Y. X and Y will be the same size with at least 2 elements. They will contain positive or negative floats. Input can be taken in any reasonable format.

Output

The values a and b in the least squares regression line (LSRL) for the data in X and Y, where a is the y-intercept and b is the slope of the LSRL. This page describes a way to calculate this line.

This is , so shortest code in bytes wins!

Also, built-ins are allowed!

Examples

[1.0, 2.0, 3.0, 4.0] [12.0, 15.0, 16.0, 17.0] -> A: 11.0 B: 1.6
[1.5, 1.5, 51.0, -15.0] [2.0, 1109.0, 0.003, 2.0] -> A: 314.92 B: -3.7609
[1.0, 2.0] [1.0, 2.0] -> A: 0.0 B: 1.0
[-15.0, -13.0, -163.0, -12.25, -14.41, 100000.0, -630.0, -135.0] [-142531.0, -12.0, 153.0, -135.0, 135.0, 16.0, 21.0, 0.0] -> A: -20285.0 B: 0.20121
[3.0, 5.0, 7.0, 9.0, 11.0, 13.0] [2.0, 4.0, 6.0, 8.0, 10.0, 12.0] -> A: -1.0 B: 1.0
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  • \$\begingroup\$ 1. Use the full name in the title, because the title will be shown in contexts where the body isn't. 2. What kind of numbers will X and Y contain? The test cases use signed integers, but can answers assume that all inputs will be integers, or that all inputs will be floating point numbers? 3. In some contexts, a quadratic can validly be described as a least squares regression line. It would be better to move the definition which makes it clear that it's a linear polynomial to the introduction, before the section on input, rather than having it in the section on output. \$\endgroup\$ – Peter Taylor Oct 22 '16 at 20:55
  • \$\begingroup\$ 4. There's more than one way to calculate the gradient, and the method described is not the best one. I would suggest removing that section entirely and having a link to en.wikipedia.org/wiki/Simple_linear_regression in the introduction. \$\endgroup\$ – Peter Taylor Oct 22 '16 at 20:56
  • \$\begingroup\$ @PeterTaylor, I have edited the question. Is it better now? \$\endgroup\$ – Daniel Oct 22 '16 at 21:26
  • \$\begingroup\$ Every math language has a builtin for this so it's just solve(x,y). Even without the built-in linear solver, this is just the pseudoinverse of (1,x) multiplied with y. \$\endgroup\$ – Angs Oct 23 '16 at 6:04
  • \$\begingroup\$ I disagree with Peter - for the sake of self-containedness, you should include at least one method of computing the LSRL (and keep the link in case people want to see more methods). \$\endgroup\$ – Mego Oct 24 '16 at 6:50
1
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2D Poor Man's Plotting!



Introduction

Surely you've also come across the problem where you have a multi-dimensional function at hand and want to visualize it (it's just such an everyday problem!). So we need a (programmatic) solution to this. A memorable solution, thus obviously the shortest solution is best!

Specification

Input

Your (primary) input will be a function that maps two floats onto another float.

Additionally there are six other parameters (floats), which you may take explicitely or hard-code:

  • StartingValueX: 0
  • StartingValueY: 0
  • EndingValueX: 10
  • EndingValueY: 10
  • StepSizeX: 1
  • StepSizeY: 1

You may take these parameters using your preferred method of input, but please document it (especially how the function should be passed).

Output

The output is a formatted string or a printed output (whatever pleases you).

What to do?

The introduction already hinted it:
Given a function that takes two floats as inputs, iterate it two-dimensionally and print the resulting values. So the top left entry is the result of the evaluation at (StartValueX,StartValueY) and the bottom right entry is the evaluation of (EndValueX,EndValueY) and then you form basically a table from this by incrementing the StartValue by the respective StepSize for each iteration.

Formatting guidelines:
Between each line may be one (or more) empty lines (eg end your lines with \n\n in C).
There must be at least one white space between every output number.
All numbers with the same x-coordinate must be aligned respectively to their start.

Potential Corner Cases

You may always assume a certain function prototype is used.
If EndValue-StartValue is not an exact multiple of StepSize (which may happen because we're dealing with floats here) then you shall compute for all StartValue + k * StepSize smaller than EndValue as well as for EndValue.
You may always assume the computation results (of the function) are actually representable in your language.
You may not assume that the function is a simple mathematical function (e.g. any valid function adhering to the above conditions in your language must work).
Trailing newlines and white spaces are allowed.

Who wins?

This is code-golf so the shortest answer in bytes wins!
Standard rules apply of course.

Test-cases

Default parameters, f(x,y)=x+y
Output:

0  1  2  3  4  5  6  7  8  9  10
1  2  3  4  5  6  7  8  9  10 11
2  3  4  5  6  7  8  9  10 11 12
3  4  5  6  7  8  9  10 11 12 13
4  5  6  7  8  9  10 11 12 13 14
5  6  7  8  9  10 11 12 13 14 15
6  7  8  9  10 11 12 13 14 15 16
7  8  9  10 11 12 13 14 15 16 17
8  9  10 11 12 13 14 15 16 17 18
9  10 11 12 13 14 15 16 17 18 19
10 11 12 13 14 15 16 17 18 19 20
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1
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[Lang1] vs [Lang2] ... vs [LangN]: Battle of the golfers!

and other tags for the challenge questions, which may be a lot.

Note: I haven't figured out all the kinks out yet, all I have is a general idea that, with your help, can be put properly into an awesome challenge (I hope). The parts where my ideas are not solid yet have Notes attached to them that must be read.

Team

In the midst of the nation of SE, there lies a golf field for the community of golfers. These golfers play day and night using specialised clubs (languages) to complete difficult and challenging holes (challenges). Now it is time to see the best of these golf clubs in the game!

Note 1: First of all, this challenge is going to be language-specific. I haven't decided the languages yet, but right now I'm thinking around the lines of Java, C, C++, C# since these languages are very well known, unlike the other esoteric languages.

You, the golfer, are to choose one golf club out from these [Lang1], [Lang2], ..., [LangN]. You will team up with other players using the same golf club as you.

Note 2: Now there is supposed to be a table where the players can edit into this challenge (once I post it) to join a team. After ~1 week from the beginning of the sign-up, people will start competing in the challenge.

This will be a sort of golf relay, where every player must only complete 1 hole, no more, no less. But of course, each player may help teammates to complete the holes using the minimum number of shots (bytes) as possible. All golfers, of every team, will be playing using the same playing field, in this case UTF-8.

The Challenge

There will be a list of challenges [see Note 3] to be completed by the team. Each team member must complete 1 challenge only. After a fixed amount of time (see Note 3), all team members must have complete their assigned challenges (see Note 4). I will sum of all the bytes used by each team to figure out the winning team (see Note 5)!

Note 3: Either I will provide all the challenges, or each team member may give 1 challenge to the challenge pool. Challenges can range from anything like quines and "Hello, World" challenges, to more complicated ones, like solving advanced mathematical (pardon me) mumbo jumbo and outputting complex sequences. Every team completes all of these challenges (see Note 4).
The time that I have decided, so far, is to give the entire team 3 weeks (subject to change) to complete their challenges.

Note 4: Each team member complete 1 challenge. However, if the team sizes are different, the team with the greatest number of members will have to complete all of the challenges. The other teams only have to complete as many challenges as members, so that there will be one for every member.

Note 5: The scoring will be the number of bytes used by each team, summed up, and then divided by the number of challenges completed.

Answering

Here is the format to each answer:

#Language, challenge-number, byte-count in UTF-8

for example:

#Java, #34, <s>463</s> <s>444</s>  <s>442</s> bytes

Summary

To sum it up, here is the process that this challenge goes through:

  1. People who want to play must choose one team to be on, if they want to play.
  2. After registration is over, the games begin: each player is to choose only one challenge and give a golfed answer. (Other players of the same team are allowed to help teammates)
  3. After some time, when all the challenges are attempted (one for every person, if people haven't answered in this time, they won't be counted towards the challenge), I will calculate the score of each team (using the total bytes used).
  4. Leaderboard is announced and the winning team walks away with all the glory!

Comment any ways this challenge can be improved. My general idea is to implement a team game, instead of the standard free-for-all.

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1
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King of the Hill: Moon Rockets

This is a challenge where you code bots to compete in an arena. In this case, you code a rocket flying over the Moon. Your goal is to shoot down enemy rockets, while not running out of fuel and crashing into the Moon.

Environment

Unlike many KOTH challenges the playing field is continuous, rather than discrete. You are provided with variables for your position, velocity, and the direction you are facing. Each turn, you are given a list of all the rockets you can "see" (all rockets less than 10 units away). You return a turning speed, thrust and whether you want to fire missiles.

Arena

The arena wraps left-right. There is a floor; if you crash into it going faster than 4 m/s, you will explode. There is no ceiling, but you do have a limit of 10 fuel units. This can be refueled by landing on the floor going less than 4 m/s.

Missiles

Every turn, you have the option to fire missiles. Missiles go in the direction you are pointing, at a constant velocity 5 m/s faster than you were when you fired. If they come within a 1m radius of another rocket, they explode and destroy it.

Gravity

Gravity is a constant force of 1 downward. With a max thrust of 2, you can accelerate at an equal rate in the opposite direction.

Pastebin for current controller code: http://pastebin.com/FNyjrJfr
No tournament code is in place yet.

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  • \$\begingroup\$ Possibly relevant: Spacewar KotH \$\endgroup\$ – trichoplax Oct 25 '16 at 20:11
  • \$\begingroup\$ The controller seems to set the step size at 0.5s. Does that give enough time to take evasive action at all, given the missile speed and sight range? (Even discounting step size, with max thrust of 2, it seems like it's going to be hard to outmaneuver something going possibly several times faster) \$\endgroup\$ – Geobits Oct 25 '16 at 20:11
  • \$\begingroup\$ Additionally related to step size, how are collisions handled? If I'm a meter away from you and fire a missile that goes 7m/s, can it miss by overshooting in that half second? \$\endgroup\$ – Geobits Oct 25 '16 at 20:14
  • \$\begingroup\$ Can spaceships collide with each other, or only the surface? \$\endgroup\$ – Geobits Oct 25 '16 at 20:15
  • \$\begingroup\$ 1. Continuous presumably means floats, which means possible disagreements over the results (because e.g. Java doesn't strictly apply the IEEE-754 spec unless you tell it to). 2. The spec should say at the very least what information is available to the bots. Does the "list of all the rockets you can "see"" include velocity, angular velocity, etc. or just position? \$\endgroup\$ – Peter Taylor Oct 25 '16 at 20:24
  • \$\begingroup\$ I assume one win condition is "last rocket flying", but what about stalemates? Is there a "last turn", since it seems like a couple pacifists could land/refuel forever? \$\endgroup\$ – Geobits Oct 25 '16 at 20:27
  • \$\begingroup\$ @Geobits - the collisions are handled point-by-point, so yes, you could miss someone right in front of you if you have a high closing speed. I think evasion is possible as long as you have at least 1 step of warning. \$\endgroup\$ – Skyler Oct 26 '16 at 13:10
  • \$\begingroup\$ @Geobits Spaceships can't collide in the current code. If they could, what should define a "collision"? Currently they are modeled as point objects. \$\endgroup\$ – Skyler Oct 26 '16 at 13:11
  • \$\begingroup\$ @PeterTaylor they can access velocity etc. as well as position. I think this might be required as if a rocket is moving fast you need to lead it with the missile. \$\endgroup\$ – Skyler Oct 26 '16 at 13:12
  • \$\begingroup\$ @Geobits I could add a condition that limits the total turns. Does 50 turns seem reasonable? \$\endgroup\$ – Skyler Oct 26 '16 at 13:13
1
\$\begingroup\$

C Compiler

Implement a basic C Compiler.

You do not need to implement the libraries. Compiler would output an object file containing a function, that would be linked with some libraries using GNU binutils ld and run.

No function calls, unions, structs, casts will be used in the test cases.

Test case:

int test(int i, int j) {
  int x[10][20];
  int s = i + j;
  i = 0;
  j = 0;
  for(i = 0; i < 10; i++)
    while (j < 20)
    {
      j += 1;
      x[i][j] = i * j;
    }
  for(i = 0; i < 10; i++)
    while (j < 20) {
      s += x[i][j];
    }
  return s;
}

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\$\endgroup\$
  • 2
    \$\begingroup\$ What does need to be implemented? A question should ideally be self-contained, but if there's too much information to fit in the post then it should contain links to the relevant specifications. \$\endgroup\$ – Peter Taylor Oct 26 '16 at 10:08
1
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HamSort a list of strings

Given a list of strings, sort them in a manner such that the Hamming distance between each is minimal.

The Hamming distance between two strings of equal length is the number of positions where the corresponding characters do not match. For example, the Hamming distance between apple and ample is 1 since only the second characters of each do not match.

apple
ample
 *

Rules

  • This is so the shortest code wins.
  • Each string in the input list will have the same length and will consist of only the letters in the English alphabet. You may assume all to be either uppercase or lowercase.
  • If there are multiple possible solutions, you may output any number of them.

Test Cases

<to be created>
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  • 2
    \$\begingroup\$ The Hamming between consecutive pairs? If so, what is to be minimized? The sum of the Hamming distances? Their maximum? \$\endgroup\$ – xnor Oct 26 '16 at 7:32
  • \$\begingroup\$ What is (for this challenge) the hamming distance of strings without equal length? Or will the list contain only strings of the same length? \$\endgroup\$ – Laikoni Oct 26 '16 at 8:06
  • \$\begingroup\$ @xnor It's still a work-in-progress. I'd like to have the problem be minimizing the Hamming distance between the consecutive pairs, but that problem might be hard enough that the only golfy solution would be generating all permutations and testing each pair. Then a length n input would have a length n-1 Hamming distance array where each value is minimal. If you have better ideas that could still capture the spirit of this, feel free to suggest them. \$\endgroup\$ – miles Oct 26 '16 at 8:33
  • \$\begingroup\$ @Laikoni Yes, Hamming distance is only defined between strings with equal length and one of the rules was that the input array would only contain strings with equal length. \$\endgroup\$ – miles Oct 26 '16 at 8:34
  • \$\begingroup\$ I think it's NP hard to find the path that minimizes total Hamming distance by reduction to Ham-Path. So, I wouldn't expect anything better than brute force there. \$\endgroup\$ – xnor Oct 26 '16 at 9:00
1
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How fast (slow) is your language?

This is a question both to test your coding skills but also to speed benchmark your favorite language. The code snippet will make a table of the fastest code per language. It is related to previous [challenge]1 so you may find some of the code there a useful starting point.

The challenge is to write the fastest code possible for computing the permanent of a matrix whose entries are floating point in the range -1 to 1.

The permanent of an n-by-n matrix A = (ai,j) is defined as

enter image description here

Here S_n represents the set of all permutations of [1, n].

As an example (from the wiki):

enter image description here

In this question matrices are all square and will only have the floating point values in the range -1 to 1 (excluding both ends). I will construct all tests in such a way that the permanent is also in the range -1 to 1.

Examples

Input:

[[-0.34389946 -0.811193  ]
 [ 0.62778788 -0.09918764]]

Permanent:

-0.47514655471

Input:

[[-0.34389946 -0.811193  ]
[ 0.4783581  -0.56636227]]

Permanent:

-0.19326906099

The task

You should write code that, given an n by n matrix, outputs its permanent.

As the output will never be bigger than 1 in absolute value you do not have to worry about overflow. However you do have to worry about numerical accuracy. All answers should be correct up to 8 decimal places.

Languages and libraries

You can use any available language and libraries you like but no pre-existing function to compute the permanent.

More to be added..Work in progress

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\$\endgroup\$
  • \$\begingroup\$ "All answers should be correct up to 8 decimal places." Are you sure this is possible? I suspect that finding the permanent has similar problems of ill-conditioning to finding the determinant. \$\endgroup\$ – Peter Taylor Oct 28 '16 at 11:37
  • \$\begingroup\$ So this is your posted permanent challenge but with floats? I don't see what that's so different as to warrant another challenge. \$\endgroup\$ – xnor Oct 29 '16 at 6:12
  • \$\begingroup\$ @xnor The only differences are a) it avoids all the big int stuff that turned out to be crucial in the last challenge and b) it will have a code snippet and will be designed to encourage answers in lots of languages. Not just fast ones. The idea is to show how slow (fast) your language is and it can serve as a fun sort of language competition/benchmark. \$\endgroup\$ – user9206 Oct 29 '16 at 7:07
  • \$\begingroup\$ @PeterTaylor That's a very interesting point. I am not sure of the answer but I was going to choose random orthogonal matrices (I need to change and add examples) so maybe ill-conditioning will be very rare? \$\endgroup\$ – user9206 Oct 29 '16 at 7:08
1
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Directional Brainf*ck Compiler/Interpreter

Challenge: Write a Brainf*ck compiler with 4 extra commands.

L Set the direction to go left
R Set the direction to go right
D Set the direction to go down
U Set the direction to go up

The original commands (altered):

+ Increment the cell one
- Decrement the cell one
[ Start a loop, if the cell is 0 then go to the next ]
] end a loop if the current cell is 0. Else go back to the last [ read and continue from there (in the direction you were going last time it was read.
. output the byte at the data pointer.
, accept one byte of input, storing its value in the byte at the data pointer.
> point to the cell to the right
< point to the cell to the left

Compiler/Interpreter

In this case the compiler must either convert the code to another language or be an interpreter and run the code.

This is basically a directional version of brainf*ck. Directions should work the same way they do in ><>.

The pointer should start at the tape's beginning. It must be infinite in the right direction. Left infinite is optional (if you add it -10 to the score). Upon end of code output (in any reasonable form) the current values on all the stacks. If a ] is hit before a [ output a warning (with a message of your choosing). If a , is met at the end of the code you can do with it as you please. The program will terminate at the end of the file.

Standard loopholes apply.

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  • 1
    \$\begingroup\$ So, what does ] do \$\endgroup\$ – feersum Oct 23 '16 at 19:05
  • \$\begingroup\$ Taken from Wikipedia: if the byte at the data pointer is nonzero, then instead of moving the instruction pointer forward to the next command, jump it back to the command after the matching [ command. @feersum \$\endgroup\$ – XiKuuKy Oct 24 '16 at 0:51
  • 1
    \$\begingroup\$ You don't need to tell me what it does in brainfuck. I'm asking you, what does it do in this language you're defining here? \$\endgroup\$ – feersum Oct 24 '16 at 1:02
  • \$\begingroup\$ @feersum Oh okay. If the byte at the data pointer isn't 0 then instead of going to the next command. Go back to the last [ found. Should I add that to the challenge description? \$\endgroup\$ – XiKuuKy Oct 24 '16 at 1:39
  • \$\begingroup\$ That description doesn't accord with the normal interpretation, which goes to a matching bracket, rather than the last one found. And it still doesn't clarify how it will interact with the two-dimensional aspect. In particular, what direction will the instruction pointer travel after jumping to a [? \$\endgroup\$ – feersum Oct 24 '16 at 2:01
  • 1
    \$\begingroup\$ @feersum it should go in the same direction it was going last time it was parsed I guess. I thought the last [ parsed would be better since I can't imagine matching brackets in 2D language. \$\endgroup\$ – XiKuuKy Oct 24 '16 at 2:06
  • \$\begingroup\$ You need to specify the behavior in the challenge specification. Personally I don't see an issue with jumping back to the command after the last [ encountered, continuing in the same direction. 1D programs in this extension that didn't use any of LRDU would be compatible with regular brainfuck with that behavior (assuming no mismatched braces). \$\endgroup\$ – Mego Oct 24 '16 at 6:47
  • \$\begingroup\$ Also, what does [ do if the cell is 0.... \$\endgroup\$ – feersum Oct 24 '16 at 19:03
  • \$\begingroup\$ @feersum Jump to the next ] in the current direction, presumably. That needs to be specified too, though. \$\endgroup\$ – Mego Oct 24 '16 at 21:09
  • \$\begingroup\$ @trichoplax Done. \$\endgroup\$ – XiKuuKy Oct 25 '16 at 3:43
  • \$\begingroup\$ Since tags can't be added to an answer, you can use [tag:code-golf] to show the tags you are going to use, so it won't be necessary in the title. \$\endgroup\$ – trichoplax Oct 25 '16 at 9:17
  • \$\begingroup\$ If it's going to be a compiler/interpreter, it may attract more competitors if that is included in the title. \$\endgroup\$ – trichoplax Oct 25 '16 at 9:18
  • \$\begingroup\$ Is this ready to post? \$\endgroup\$ – XiKuuKy Oct 28 '16 at 14:36
  • 1
    \$\begingroup\$ It's missing a lot of info. (1) The position and direction of instrucitons pointer at the beginning. (2) What happens upon reaching an edge of teh code. (3) What happens if ] is hit before any [. (4) The usual BF-specific stuff: (a) behavior of , on EOF (b) Integer range of cells (c) whether tape should be infinite in one direction, both, or something else. (5) How does the program terminate, if at all. \$\endgroup\$ – feersum Oct 29 '16 at 2:52
1
\$\begingroup\$

Modular Reverse Recursion Sequence

Given any number n > 0, let r represent the reverse of the number n. Iterate until the final result is zero, passing the result of each iteration back into the function using recursion or a methodology of your choice by performing the below operation:

  • If r > n for that iteration the result is r % n.
  • If n > r for that iteration the result is n % r.
  • If n % r = 0 or r % n = 0, you terminate iteration.

Take the intermediate result of each execution and store them in an array for the final answer.

Lets walk through an example where n=32452345.

54325423 % 32452345 = 21873078 # r > n, uses r % n
87037812 % 21873078 = 21418578 # r > n, uses r % n
87581412 % 21418578 = 1907100  # r > n, uses r % n
1907100 % 17091 = 9999         # n > r, uses n % r
9999 % 9999 = 0                # r % n = n % r = 0, terminated

Result: [21873078, 21418578, 1907100, 9999]     

Another example n=12345678:

87654321 % 12345678 = 1234575 # r > n, uses r % n
5754321 % 1234575 = 816021    # r > n, uses r % n
816021 % 120618 = 92313       # n > r, uses n % r
92313 % 31329 = 29655         # n > r, uses n % r
55692 % 29655 = 26037         # r > n, uses r % n
73062 % 26037 = 20988         # r > n, uses r % n
88902 % 20988 = 4950          # r > n, uses r % n
4950 % 594 = 198              # n > r, uses n % r
891 % 198 = 99                # r > n, uses r % n
99 % 99 = 0                   # r % n = n % r = 0, terminated

Result: [1234575, 816021, 92313, 29655, 26037, 20988, 4950, 198, 99]

A final example n=11000:

11000 % 11 = 0 # n % r = 0, terminated

Result: []
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  • 1
    \$\begingroup\$ If you have to include 0 as the final element, it might be better to say "if n = 0, terminate", since terminating when n=r doesn't really include 0, because the final modulus (e.g. 9999%9999) was never done. \$\endgroup\$ – Geobits Nov 1 '16 at 18:22
  • \$\begingroup\$ @Geobits Edited to remove 0 from the list of final results, nice catch. That was the only part I did manually. \$\endgroup\$ – Magic Octopus Urn Nov 1 '16 at 18:33
1
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Table Math

You should which side of a table is the oldest, from ASCII art. I think the best way to explain is with an example, so here is one.

You have a table, made out of +, |, and -. Here is one.

+--+
|  |
|  |
|  |
+--+

It will alway be a rectangle, just not always square (but it can be square). There will also be people around the table, marked by the letters A-Z. There will never be too many people on a side, or less than one. Just to make it harder, the people will not always be in order, like this:

  P
 +--+
I|  |
O|  |Q
 |  |J
 +--+
   U

There will never be anybody next to a plus sign(+). You will be given input on how old each member is, separated by a newline, from the first letter that appears alphabetically (I in this example) to the last letter that appears alphabetically (U in this example), like this:

20
8
31
56
6
56

As seen here, ties are allowed. You should then output the sides with their ages separated with a space, in order from oldest to youngest, like this.

Top 56
Bottom 56
Left 51
Right 14

Note that for everything in this challenge, you can choose the capitalization of the letters, even the input. The winner is the submission with the shortest code.

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\$\endgroup\$
1
\$\begingroup\$

Simplified maze-solver

A spin-off from this question Textual maze solver

Write a program, that will take an bunch of 0's and 1's as it's input (see below), and a half-solved maze as it's output. The program should take 1's as walls and 0's as corridors. The output should should show 99's as walls and a number as the distance from the start of the maze. The maze should have no real entrance/exit; instead, the entrance is the square in the 2nd column of the 2nd row.

Examples (allowed cases):

Input               Output

1 1 1 1 1 1         99 99 99 99 99 99
1 0 0 1 0 1         99 00 01 99 05 99
1 1 0 0 0 1   -->   99 99 02 03 04 99
1 0 1 1 0 1         99 10 99 99 05 99
1 0 0 0 0 1         99 09 08 07 06 99
1 1 1 1 1 1         99 99 99 99 99 99 

{{1, 1, 1, 1, 1, 1, 1, 1, 1},         99 99 99 99 99 99 99 99 99
 {1, 0, 0, 0, 1, 0, 0, 0, 1},         99 0  1  2  99 16 17 18 99
 {1, 1, 1, 0, 1, 0, 1, 0, 1},         99 99 99 3  99 15 99 19 99
 {1, 0, 0, 0, 1, 0, 1, 0, 1},   -->   99 6  5  4  99 14 99 20 99
 {1, 0, 1, 1, 1, 0, 1, 0, 1},         99 7  99 99 99 13 99 21 99
 {1, 0, 0, 0, 0, 0, 1, 0, 1},         99 8  9  10 11 12 99 22 99
 {1, 1, 1, 1, 1, 1, 1, 1, 1}}         99 99 99 99 99 99 99 99 99

Examples (not allowed outputs and inputs):

11111 10101 10101 10001 11111  --> 9999999999 9900990699 9901990599 9902030499 9999999999

Notes:

  • as seen above, the input and output must be bunch of numbers separated by whitespaces, commas, full stops, newlines, parenthesis (and so on), and mustn't be in a single row

  • you can output 01 instead of 1

  • cases where the distance is over 99 don't need to be covered

  • the program doesn't need to solve the maze, just to find the distance from the start

  • two fields connected diagonally aren't next to each other

  • it's , so the shortest answer in bytes wins!


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  • \$\begingroup\$ it makes more sense to show walls as ## or || etc, instead of an integer \$\endgroup\$ – FlipTack Nov 5 '16 at 21:56
  • \$\begingroup\$ The restrictions on the format on the output and inputs don't add anything to the challenge (imo) : the interesting part is solving the maze. \$\endgroup\$ – Dada Nov 6 '16 at 10:56
  • \$\begingroup\$ @Dada They allow the program to be shorter, at least in most languages I know. \$\endgroup\$ – RudolfJelin Nov 6 '16 at 13:55
  • \$\begingroup\$ @Flp.Tkc See the comment above. \$\endgroup\$ – RudolfJelin Nov 6 '16 at 13:56
1
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Defs need to fix up layout

[Very much a WIP]

Maze battle

In this challenge, bots will team up, navigate around a maze and try to destroy the enemy team's artifact, and protect their own.

A maze might look like this. Note that the bots will receive numbers rather than ascii art, which represent their vision, and the objects they see.

+---------+-+---+-------+++-+-+---+-+-------+-+-----+
|         | |   |    #  | | | |   | |       | |     |
+-+ +-+-+ + + + +-+-+ +-+ + + + + + + + +-+-+ +-+ + |
|   |         |         |     | |   | | |   |     | |
| +-+-+ + +-+ +-+ + + +-+ + +-+ +-+ +-+ + +-+ +-+ + |
|       | |   |   | |     | |   |         | |   |   |
| +-+-+-+ +-+-+-+ + + + + +-+ +-+-+ +-+ + + + +-+ + |
|   |     |       |   | |   |   |     | | |       | |
| + + +-+-+ +-+ +-+ +-+ +-+ + +-+ + + + + + +-+ + + |
| |       |                 | |   | | |     |   | | |
| + + + +-+-+-+-+ +-+-+-+ + + +-+ +-+ + +-+-+-+ +-+-+
| | | |     |   | | |     |     |   | | |           |
| +-+ +-+ + +-+ +-+ +-+-+ +-+ + + + + + +-+-+ +-+ + |
|   | |   | |           | |   | | | |   | | |     | |
| +-+ + +-+ +-+ + + + +-+-+-+ +-+ +-+-+ + + + +-+ + |
|     | |       | | |   | | | | | |         |   | | |
| + + +-+ + + + + +-+ +-+ + +-+ + +-+ +-+-+ +-+ +-+-+
| | |   | | | | |   |   |       | |   | |       |   |
| +-+ + + +-+ +-+-+-+ +-+ +-+-+ + + +-+ + +-+-+ +-+ |
|   | |   |         |       |   |       |   |       |
+-+ +-+-+ +-+ +-+ +-+ + +-+ + + + +-+ +-+ +-+ + +-+-+
|   |   |   |   |   | | |     |     |   | |   |     |
| + +-+ +-+ + +-+-+-+ + + + +-+-+-+ +-+ + + +-+ +-+ |
| |       |   |   |     | |         | |   | |       |
| +-+-+ + +-+ +-+ + +-+-+-+ + + + +-+ +-+ +-+-+ +-+ |
| |   | | | |       | |   | | | | |   |     |     | |
+-+-+ + +-+ +-+-+-+-+ +-+ +-+ +-+ + +-+-+ +-+ +-+ + |
| | | | |   |           |     | |     |       | | | |
| + + +-+-+ + +-+ +-+-+ + +-+-+ +-+ +-+-+-+ +-+ +-+-+
|   |     | | |             |   | |   | |     |     |
+-+ +-+-+ + + + +-+ +-+-+-+ +-+ + +-+ + +-+ +-+ +-+-+
|   | |   |   |   | |     | |   |     |   |       | |
| +-+ + +-+-+ + +-+ + + +-+-+ + + + + + +-+-+ + + + |
|       | |           |       |   | | | |     | |   |
| +-+-+ + +-+ + +-+-+ + + +-+ + +-+-+ + +-+ + + +-+ |
|   | |   |         | | | |   |     |   | | | | |   |
+-+ + + + + + + +-+ + +-+-+-+-+ +-+-+ +-+ +-+-+ + +-+
|       |   | | |           |     | | |   | |       |
+-+-+-+ + +-+-+-+-+-+ + +-+-+ +-+ + +-+ + + + +-+ + |
|     |   | |         |     | |     |   |       | | |
+-+ +-+ +-+ +-+ + +-+ +-+-+ + + +-+ +-+ +-+ +-+ +-+-+
|     | | |     |   |         | |           |   |   |
+-+ +-+-+ + +-+-+ +-+-+ +-+-+ +-+ +-+-+-+-+ + +-+ + |
|               | |   |                 |   | |   | |
+-+-+ +-+-+-+ + + + + +-+-+-+-+-+-+ +-+ + + +-+ +-+ |
|       |   | | |   |   |           | | | |       | |
| +-+-+ + + +-+ +-+ + + +-+-+ +-+ + + + +-+-+-+-+ + |
| |       | | | |   | |       |   |     |           |
+-+-+ + +-+-+ + + +-+ +-+ +-+-+ + +-+ + + +-+-+ +-+-+
| |   |     |   | | |   |       |     | |     |     |
| + +-+ + + + + + + + + + + + + +-+-+-+ +-+-+ +-+-+ |
|       | | | |    #  |   | | | |       |     |     |
+-------+-+-+-+-------+---+-+-+-+-------+-----+-----+

Bots receive information about their current environment. They will receive a 8 lines of numbers, representing their view in each of the directions. vision is blocked by walls, and walls only, so at the end of the line of sight is a wall.

Numbers represent the following things:

  • 0 represents a space with nothing in it.
  • 1 represents a friendly bot
  • 2 represents an enemy bot
  • 3 represents your team's artifact
  • 4 represents the enemy team's artifact

To destroy the enemy's artifact, you have to shoot it a bunch. heaps. So, you probably want to bring that artifact to your team, or your team's side, so that you can shoot it more.

When you die, you respawn after 5 turns.

At the start of the round, bots spawn into the first third of the maze on their side. when respawning, they also spawn into this area.

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  • 1
    \$\begingroup\$ Nice idea! Would be better if it was Java :D \$\endgroup\$ – user41805 Nov 6 '16 at 10:20
  • 1
    \$\begingroup\$ @KritixiLithos: No \$\endgroup\$ – Destructible Lemon Nov 8 '16 at 23:28
1
\$\begingroup\$

Format an XML file

Your task is to parse an XML snippet (not necessarily an entire file) and format it. I am explicitly making this simple to encourage extremely golfed code.

The formatter should transform XML like this:

<?xml version="1.0" encoding="UTF-8"?>
<body>
    <div class="community-option">
        <input id="communitymode" name="communitymode" type="checkbox"/>
        <label for="communitymode" title="Marking an answer community wiki encourages others to edit it by lowering the reputation barrier required to edit. However, you will not gain any upvote reputation from it. This cannot be undone.">community wiki</label>
        <a href="www.hoehel.be"><i>My inner web developer hates me</i></a>
        <b>BOLD</b>
    </div>
    <iframe/>
</body>

into formatted text like this:

?xml
body
    div
        input
        label
        a
            i
        b
    iframe

Rules

The main element does not get a indent, every layer deeper does get an extra indent. An indent is either a tab or 4 spaces.

When there are multiple root elements, they simply are added below eachother with no indentation. The ?xml element is not different from any other element.

The XML will have a space after each element name, so if there is a CDATA element, it will be formatted as <![CDATA[ (the data)]]> and will need to be formatted as ![CDATA[ at the correct indentation.

Also, the XML will not include > and < except for opening and closing elements.

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  • \$\begingroup\$ In XML, a right angle bracket > is allowed in an attribute. So perhaps include that as a test case, or explicitly state that this will not happen. Also, what qualifies as an indent? One space? Four spaces? A tab character \t? \$\endgroup\$ – Sanchises Nov 8 '16 at 11:31
  • \$\begingroup\$ 1. The example is invalid because (a) it doesn't have a single root element; (b) the input element isn't closed. 2. This isn't really pretty printing XML. It's pretty printing the element structure of XML. 3. There are a whole bunch of important test cases which are missing. CDATA. Namespaces defined at the root element. Namespaces defined on non-root elements. Elements expanded from entities. There are bound to be some others if you look at the spec. \$\endgroup\$ – Peter Taylor Nov 8 '16 at 17:08
  • \$\begingroup\$ @sanchises Reworked the question to avoid problems there. \$\endgroup\$ – vrwim Nov 8 '16 at 21:11
  • \$\begingroup\$ @PeterTaylor (a) I'll include that it can be a snippet. (b) Didn't notice it, took some HTML from stackoverflow source code, don't blame me :) 2. Renamed to "formatting" the XML 3. Added workaround for the special cases I could find. \$\endgroup\$ – vrwim Nov 8 '16 at 21:15
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