# Sandbox for Proposed Challenges

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

Sandbox FAQ

## Posting

To post to the sandbox, scroll to the bottom of this page and click "Answer This Question". Click "OK" when it asks if you really want to add another answer.

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

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

## Discussion

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

• Parts of the challenge you found unclear
• Comments addressing specific points mentioned in the proposal
• Problems that could make the challenge uninteresting or unfit for the site

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

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

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

## Other

Search the sandbox / Browse your pending proposals

The sandbox works best if you sort posts by active.

To add an inline tag to a proposal use shortcut link syntax with a prefix: [tag:king-of-the-hill]. To search for posts with a certain tag, include the name in quotes: "king-of-the-hill".

Get the Sandbox Viewer to view the sandbox more easily!

# "Square Root of Pi(e)"

A pie (r=3) is drawn as such:

  @@
@@@@
@@@@@@
@@@@
@@


Pretending that it's a perfect circle, the square root of such a pie would be sqrt(PI*32) = 3sqrt(PI) ~ 5.317. Now take a square out of the pie, whose area is closest to the square root of the pie. In this case it would be a square of area 4. Therefore, you can output:

  @@
@@@@
@@  @@
@  @
@@


Yep, I took a square out of the pie, how do you like that?

r=7

      @@
@@@@
@@@@@@
@@@@@@@@
@@@@@@@@@@
@@@@@@@@@@@@
@@@@@@@@@@@@@@
@@@@@@@@@@@@
@@@@@@@@@@
@@@@@@@@
@@@@@@
@@@@
@@ 

7*sqrt(PI) ~ 12.407. Closer to 3x3 than 4x4 square.

      @@
@@@@
@@@@@@
@@@@@@@@
@@@@@@@@@@
@@@@@@@@@@@@
@@@@@@@@@@@@@@
@@@@@@   @@@
@@@@@   @@
@@@@   @
@@@@@@
@@@@
@@ 

### Specifications:

1. Input will be only a "pie" with integer radius of at least two. As you can see, the longest row has 2r @s, and the smallest rows have 2 @s.
2. You can use a symbol other than "@".
3. You can take a square out of the inside or the edge.
4. Approximate PI to at least 3.14.

Bonus: Valid answers that are in a language with food-related name get a free upvote!

• You don't ever define How one forms the pie shape, and in general you seem to be lacking specification. – Wheat Wizard Sep 3 '17 at 3:37

# The Best Question

This site gets a variety of questions: the good, the bad, the ugly. However, I've noticed some patterns that I think will help us find The Best Question (of a given week).

## Procedure

You are given a date in a human-readable format of your choice as input. You need to find the best question from that week. The week starts on Sunday and ends on Saturday. Click on the link for a valid query to use if the input is Aug 31, 2017. Note that when using the API without a key you can use UNIX epoch time or YYYY-MM-DD to specify the dates (info here). Since this site gets only about 45 questions a week, you can assume that no more than 100 questions will be asked in a given week in order to avoid pagination.

## Scoring

First of all, closed questions are disqualified. Next, here is the formula for Question Rating (QR)1, given Question Score (S) and Number of Answers (A):

The thinking is that there are two kinds of questions that undeservedly get a very high question score: 1) the ones that are easy and get a lot of answers, and 2) the ones that are so difficult that they get few or no answers. I've determined that the best questions have a QuestionScore:Answer ratio of about 3:2.

## Output

All you have to do is output the full URL of the question that got the best question score. If multiple tie, you can output them all or just one.

## Example

Here's a list of 8 imaginary questions, with their question score followed by the number of answers they received, and their resulting QR:

1. +6, 23A -> -0.333
2. +10, 0A -> 7.78
3. +8, 4A -> 7.56
4. -2, 6A -> -4.44
5. +5, 3A [closed] -> DQ
6. +20 2A -> 16.22
7. +24, 40A -> 16
8. +15, 14A -> 13.67


So the winner is question 6. Output its URL.

## Note

You don't need to handle the rare edge case when there are no valid questions in a given week.

1Disclaimer: This scoring system is just a joke.

Suggestions on formula and other stuff welcome.

• Is that abs((QuestionScore/2)-Answers)/2 or abs(QuestionScore/(2-Answers))/2? – Shaggy Sep 1 '17 at 12:05
• Hopefully this looks a bit better. – geokavel Sep 1 '17 at 15:29

# Extend the Pattern

Given a raster image with a lattice pattern, extend it to twice the size of the input image in both directions.

### Details

The input image is a section of an infinite repeating pattern defined by two vectors u=(ux,uy),v=(vx,vy) with integer entries, that are linearly independent. This means that both vectors are nonzero and do not point in the same direction. The pattern is defined such that the pixel at a point p = (x,y) has the exact same colour as the pixel at

q := p + s*u + t*v


for every integer s,t. This means if you know the colours of the pixels within the fundamental parallelogram Z = { s*u + t*v | s in [0,1),t in [0,1)} and corresponding vectors u,v you can extend the pattern to an arbitrary size. The goal of this challenge is finding the pattern and extend the image.

### Specs

• You can take the input image in any non-compressed image format that allows for at least 3 colours, this includes e.g. matrices, 2d arrays or strings.
• The input method must match the output method. That means if you read a .png file as input, you must also write a .png file as output, or if you take the input via console, you must also print the output via console e.t.c.

### Examples

• Is there freedom to choose which quadrant of the output image corresponds to the input image? – Peter Taylor Sep 3 '17 at 18:05
• You need to add some harder test-cases - at present you can just check for overlaps, tile "infinitely" then crop. – wizzwizz4 Sep 4 '17 at 16:25
• @PeterTaylor Good question, I think I will leave the direction arbitrary. – flawr Sep 4 '17 at 19:53
• @wizzwizz4 I think this method works in any case, or do you have an example in mind where this does not work? – flawr Sep 4 '17 at 19:54
• @flawr One where there's less than one copy of the parallelogram... wait, that wouldn't prevent the overlap technique from working. – wizzwizz4 Sep 4 '17 at 19:58

# Golf a Brainfuck compresser.

The eso-lang Brainfuck only has 8 instructions that do something: +-><[],. so in theory you could represent them in 3 bits. You could store 8 instructions in 24 bits or 3 bytes.

## BrnFck

This is compressed brainfuck an instruction will be represented by its bits.

1. + : 000
2. - : 001
3. > : 010
4. < : 011
5. [ : 100
6. ] : 101
7. , : 110
8. . : 111

This is a language counted in bits, 8 bits is 1 byte depending on the challenge you may round up or keep a decimal.

## The goal

Write the shortest program that can compile any inputted brainfuck code to BrnFck code:

• You can choose how you output it, byte,bit/boolean arrays and output streams are all acceptable. Just printing ASCII-letters is too.
• You can do anything (including crash) if the input isn't valid code or contains a non-bf character.

And can compile the BrnFck code back to Brainfuck (or any other language (except BrnFck)). You may ask which way you want to compile or write 2 separate programs/functions and sum their scores.

If you post the code online (for example as an answer) this should automatically allow BrnFck as a language in all future challenges!

## Scoring

If you use brainfuck you can divide your bytes by 2.

If you use BrnFck you can divide your bytes by 4 (let's get some recursion going here).

1 bit will be counted as 0.125 bytes (please put both in the title) so decimal byte scores are allowed.

## Tags

brainfuck,code-golf,...

• This encoding doesn't really work since no sensible architecture allows partial bits. Since each 3 bit word is already used, there is no way to distinguish say ,+. from ,+.. if you happen to fill the remaining bits in that way. That said, it isn't totally required for the question for this to work. Otherwise, the bonuses and scoring are needless and confusing, so I'd recommend removing them. – FryAmTheEggman Sep 3 '17 at 16:57
• Nearly every byte score on PPCG is decimal (base 10): I think you mean that fractional byte scores are possible. To deal with the padding problem, I suggest that you specify that where one or two padding bits are required, 0 should be used; and where three to seven are required, the padding should be 101 followed by as many 0s as necessary. Since [] must be balanced, this allows unambiguous detection of the padding on decompression. Then make sure to include a test case which ends in ] and requires no padding... – Peter Taylor Sep 4 '17 at 8:02

# Program that allows the user to edit it's own source code

Write a program that displays and allows the user to view, edit and save it's own source code.

• If no edits are made, the output file should be the same as the program, and hence executing it should allow the user to edit the program's code again. (ie a quine)
• If the code has been edited in a sensible way, running the program again should display the edited code. The definition of 'sensible' is left flexible to prevent this being impossible - as the source code can be edited, a user can obviously edit the program in such a way that it no longer displays it's source code.

The standard quine rule applies: no reading the source file directly.

Additional Notes and things to consider:

• How robust is your program? What percentage of your program can be edited (sensibly) before it stops displaying it's own source or saving the edits you made.
• Both overwriting and saving with a different filename are valid ways for the program to save it's new code
• If it is a compiled language, the program does not have to invoke the compiler or do the compiling itself after saving.
• This is a code challenge not code golf. Robustness, interface and 'coolness' of the solution are favoured over brevity.

• Extra, uh, points(?!) if your program can identify errors in the quine before saving.

Is this a feasible challenge? Does it need clarification?

• If the only winning-criteria is "Percentage of the characters which can be changed without breaking it" then the answerer can arbitrarily pad their score with an irrelevant string if their language has very versatile quining capabilities. The other things "favored" only really count if it's a popularity-contest and challenges with that tag are discouraged. – Kamil Drakari Sep 7 '17 at 21:07
• Do you have any suggestions on how to score it? I can't think of any cross-language methods. – sdfgeoff Sep 7 '17 at 21:21
• Currently you are scoring it as (characters that can change / total), You could square or cube the total to incentivise golfing, that way padding can only hurt you. However you want to watch out for very short programs that make little effort to complete the task but by virtue of their shortness are highly scoring. – Wheat Wizard Sep 17 '17 at 0:35

# Prime Number Locator

Given a prime number p > 1, determine at what index p appears in A000040.

• You may 0 or 1 index, meaning 2 can return 0 or 1.
• If you are given a non-prime number you must return -1.
• If you are 1-indexing you may return 0 instead, or still return -1.
• Your time complexity must be less than O(n): Please explain your calculations in the answer.

First 10 return values (0-indexed):

[2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
[0, 1, 2, 3,  4,  5,  6,  7,  8,  9]


This is : Reduce your byte-count to win.

• Related – H.PWiz Sep 8 '17 at 17:41
• @H.PWiz, I'd call that a dupe; the count is the index. – Shaggy Sep 9 '17 at 11:48
• @Shaggy This one is restricted-complexity though – H.PWiz Sep 9 '17 at 12:00
• o(n) is impossible: this isn't a problem which can be solved without reading all of the input. If that were relaxed to O(n) I think this would fit the "Too broad" close criterion because a properly explained answer would be a (very good) doctoral thesis. The current state-of-the-art algorithms are O(2^(2n/3) + epsilon), so a polynomial algorithm would already be impressive, and a linear one would be astounding. – Peter Taylor Sep 11 '17 at 8:59

# Do the line segments cross?

Description: Today, we're going to do some geometry: We have two line segments and want to find out where they cross! A point is a pair of two integers being the x and y coordiantes of said point. If your calculations result in non-integers, you continue with the integer closest to your result.

I/O: You are given the two segments in form of 8 integers representing the 4 end points. You may take them in the order that fits you best, but you have to state the ordering. The output consisting of the point where the lines intersect, or null, an empty string or something similar, but no undefined behavior. You may use STDOUT, a file etc. to write your output.

This is - the shortest answer in bytes wins!

• Can I take 4 tuples (x,y) instead? – H.PWiz Sep 8 '17 at 17:46
• Of course. Are you golfing in Haskell? – racer290 Sep 8 '17 at 18:03
• I'm not golfing now. Many languages have tuples. – H.PWiz Sep 8 '17 at 18:05
• This is just a subset of this challenge. – AdmBorkBork Sep 8 '17 at 19:48
• Only up to a certain degree. The challenge you mentioned is ok with a truthy/falsey value. That makes a difference in chosing your "algorithm". – racer290 Sep 9 '17 at 5:17

...?

# Fork for n times

TL;DR: fork up to n times, than hang forever

Relevant chat discussion

Your challenge is to make a program / function that calls itself twice or uses some other method of creating copies of itself that create copies of itself, etc.

However, to avoid crashing the system, your program limits itself before it forks to death. Given an input n, your program should stop forking when it has n total copies of itself (including itself), and keep running forever with n total copies of itself.

# Meta

• Under-specified?
• Is the min of 500 good?
• Tags?
• Better title?
• It's not exactly a dupe of this one, but that one is the same spirit, and it's closed and locked, so I wouldn't expect this to be well received. Also see this and this – DJMcMayhem Aug 22 '17 at 21:41
• @DJMcMayhem see edits – user58826 Aug 22 '17 at 22:05

[tag:H̸̡̪̯ͨ͊̽̅̾̎Ȩ̬̩̾͛ͪ̈́̀́͘ ̶̧̨̱̹̭̯ͧ̾ͬC̷̙̲̝͖ͭ̏ͥͮ͟Oͮ͏̮̪̝͍M̲̖͊̒ͪͩͬ̚̚͜Ȇ̴̟̟͙̞ͩ͌͝S̨̥̫͎̭ͯ̿̔̀ͅ]

# Parse HTML with regex!

Alternate titles:

# Background

Don't parse HTML with regex. It always fails and sometimes summons Cthulhu.

But, because PPCG is different, we will parse HTML with regex.

And not easy, beginner HTML. HTML with comments, attributes with no quotes, HTML in script tags not commented out and much more. Can you write a regex to parse that?

# The challenge

Your challenge is to make a regex that matches valid HTML tags. Don't match comments, don't match invalid HTML, don't match HTML in comments, just match valid HTML tags. Each full regex match is one HTML tag.

Your input HTML will never contain commas. You will try to get the most points possible by successfully matching the HTML tags and not the text in as many inputs as possible. Whoever gets the most points wins. Please say at least 1 regex flavor that your regex works with.

You are not allowed to use regex features to execute language code. (Sorry, Perl)

The length of your regex is irrelevant, this is not code golf.

# Test cases

Here are the test cases. You can also find them at https://hastebin.com/raw/mikaxakipe.txt.

1,1,<b>HTML!</b>,<b>,</b>
2,1,<i><b>HTML</b></i>,<i>,<b>,</b>,</i>
3,1,a < b implies b > a,
4,2,<img alt=text>Img,<img alt=text>
5,2,<a href = "http://example.com">Example Domain</a>,<a href = "http://example.com">,</a>
6,2,<hr><br/>,<hr>,<br/>
7,2,<div id ="hi" class="what">What</div>,<div id ="hi" class="what">,</div>
8,3,<a>fake</>,<a>
9,3,Self-closing <img src = "self-closing.jpeg" />?,<img src = "self-closing.jpeg" />
10,3,<self-closed/>O_O<unclosed>,<self-closed/>,<unclosed>
11,3,Do<yOU>like<LoTs>of<mIXeD><cAsE>?,<yOU>,<LoTs>,<mIXeD>,<cAsE>
12,3,Wh<a b='c'd="e">at?,<a b='c'd="e">
13,3,Hi<p data-hi=3>hihihi</p>,<p data-hi=3>,</p>
14,4,<a"oops">Oops,
15,5,<!-- <b><!--hi--><i>,<i>
16,5,<0>NOT VALID</0><h0>fine</h0>,<h0>,<h0>
17,5,<a a=b<>what</a>,<a a=b<>,</a>
18,6,<!-- <b><!--hi--><i>-->,<i>
19,7,<how><deep can><your nesting nesting><level></level></go>?<how>Deep</how><can><your>nesting <go x=? j><how><deep can><your nesting nesting><level></level></go>?<how>Deep</how><can><your>nesting <go x=? j><how><deep can><your nesting nesting><level></level></go>?<how>Deep</how><can><your>nesting <go x=? j></your></can></your></deep></how></your></can></your></deep></how></your></can></your></deep></how>,<how>,<deep can>,<your nesting nesting>,<level>,</level>,</go>,<how>,</how>,<can>,<your>,<go x=? j>,<how>,<deep can>,<your nesting nesting>,<level>,</level>,</go>,<how>,</how>,<can>,<your>,<go x=? j>,<how>,<deep can>,<your nesting nesting>,<level>,</level>,</go>,<how>,</how>,<can>,<your>,<go x=? j>,</your>,</can>,</your>,</deep>,</how>,</your>,</can>,</your>,</deep>,</how>,</your>,</can>,</your>,</deep>,</how>
20,7,<plaintext><b></plaintext>,<plaintext>,</plaintext>
21,7,What<img src="imgs/>lolz.png" alt = "<heh"/>,<img src="imgs/>lolz.png" alt = "<heh"/>
22,7,<b><a href = "#" title = "4 > 3">hi</a></b>,<b>,<a href = "#" title = "4 > 3">,</a>,</b>
23,10,<StYle><b title = "not in html"></style><B>HTML!</b><style></style>,<StYle>,</style>,<B>,</b>,<style></style>
24,10,<script>//<script>< /script></script><script></script><p>,<script>,</script>,<script>,</script>,<p>
25,10,<i></i this="will be removed by a browser">,<i>,</i this="will be removed by a browser">
26,10,<div id="hi" class=class="what" data-the="heck='is'this" get-good>Attributes are weird<div>,<div id="hi" class=class="what" data-the="heck='is'this">,<div>
27,10,<!--<b>Do you like comments??</b>--><p>,<p>
28,13,<textarea><script>/* *////*///*<!--</script><b>WHAT</b></textarea><i>Hi-->,<textarea>,</textarea>,<i>
29,15,<!--<b>Do you like comments??</b><script>--><script>//<!--hello</script><b>hi</b><!--What--><script>//<!-- <script> <!-- <script> --> </script><i>hello--><script></script>,<b>,</b>,<script>,</script>,<i>,<script>,</script>
30,15,<hi>hi</hi><0>hi</0><h0>hi</h0><h&>hi</h&><&>hi</&><??>hi</??><?php>hi</?php><php?>hi</php?><->hi</-><_-_>hi</_-_><h->hi</h-><_>hi</_><h-_>hi</h-_><?>hi</?><{>hi</{><h{>hi</h{></>hi<//><h~!@#$%^&*()>hi</h~!@#$%^&*()><h>hi</h><h~>hi</h~><h!>hi</h!><@>hi</@><h@>hi</h@><h!@#$%^&*()>hi</h!@#$%^&*()><@f>hi</@f><%>hi</%><;>hi</;><h>>hi</h>><h&>hi</h&><h~>hi</h~>,<hi>,</hi>,<h0>,</h0>,<H&>,</H&>,<PHP?>,</PHP?>,<h->,</h->,<H-_>,</H-_>,<H{>,</H{>,<H~!@#$%^&*()>,</H~!@#$%^&*()>,<H>,</H>,<H~>,</H~>,<H!>,</H!>,<h@>,</h@>,<h!@#$%^&*()>,</h!@#$%^&*()>,<H>,</H>,<H&>,</H&>,<h~>,</h~>
31,30,<hi>hi</hi><0 WHAT_is=HtMl>hi&<i attrubute="oops'></0><h0 attRiBu350Te="<b>oops</b><style>/*">hi</h0>*/<h&>hi</h&><&>hi</&><??>hi</??><?php>hi</?php><php?>hi</php?><->hi</-><_-_>hi</_-_><h->hi</h-><_>hi</_><h-_>hi</h-_><?>hi</?><{>hi</{><h{>hi</h{></>hi&<//><script>     &/*<h~!@#$%^&*()>*/</ script></StyLe>/*</ScrIPT>/*<b>oops</b>hi</h~!@#$%^&*()><h>hi</h><h~>hi</h~><h!>hi</h!><@>hi</@><h@>hi</h@><h!@#$%^&*()>hi</h!@#$%^&*()><@f>hi</@f><%>hi</%><;>hi</;><h>>hi</h>><h&>hi&</h&><h~>hi/*/</h~><b>oops</b>hi</h~!@#$%^&*()><h>hi</h><h~>hi</h~><h!>hi</h!><@>hi</@><h@>hi</h@><h!@#$%^&*()>hi</h!@#$%^&*()><@f>hi</@f><%>hi</%><;>hi</;><h>>hi</h>><h&>hi&</h&><h~>hi/<script></StyLe></ScrIPT><textarea><b>HE COMES</b></textarea><h!>hi</h!><@>hi</@><h@>hi</h@><h!@#$%^&*()>hi</h!@#$%^&*()><@f>hi</@f><%>hi</%><;>hi</;><h>>hi</h>><h&>hi&</h&><h~>hi</h~>,<hi>,</hi>,<i attrubute="oops'></0><h0 attRiBu350Te="<b>,<style>,</style>,<textarea>,</textarea>,<h!>,</h!>,<h@>,</h@>,<h!@#$%^&*()>,</h!@#\$%^&*()>,<h&>,</h&>,<h~></h~>


Each line is a separate test case. They are in this format:

1,1,<b>HTML!</b>,<b>,</b>
| | |            |   |
| | |            +---+- The correct output: all HTML tags in the string separated by commas
| | +- The HTML for you to parse
| +- The number of points you get if you parse this HTML correctly
+- The test case number


# Example

Let's say we have the regex /<.*?>/g (all flavors). For test case #1, it matches 2 times: <b>, and </b>. The correct output in the test case says that it should match <b> and </b>, so it is correct. Our regex gets 1 point.

Then for test case #2. Our regex matches <i>, <b>, </b>, and </i>, which is consistent with the test case so we get 1 point.

Now for test case #3. Our regex matches < b implies b >, when it should have not matched anything. We get 0 points for that.

Continuing for each test case gets us a score of 50 (out of 207, or 24.15%). Not great. Can you do better?

# Try It Online

If your regex will work with the ECMAScipt / JS flavor than you can try it here and get automatic scoring!

# Tie breaker

Here are the scoring systems. Whoever has the best score on the first wins. In the event of a tie, whoever out of the ties scores the best wins, etc.

1. Most points
2. Shortest length
3. First posted

# [insert score here] / 207 points

[insert regex here]


Explanation (optional but encouraged)

Proof of score (matched output vs. test cases, link to TIO to try it, etc.)

# Meta

• Any tie breaking for regexes with the same score, e.g. length? – Laikoni Sep 11 '17 at 5:28
• 1. This is a meta-regex question, and scoring it just on test cases means that there are already programs out there which will generate a regex that gets a perfect score. As it stands it's a pretty pointless contest. 2. I don't see a specification for an HTML tag, or even a link to one. Why, for example, is < b implies b > invalid? Without a spec it's even more a meta-regex question rather than an HTML question. 3. This isn't parsing HTML with regex. It's closer to lexing HTML with regex, and no-one said that that was impossible or would summon the Elder Ones. – Peter Taylor Sep 11 '17 at 7:50

# Matrix Decomposition

## Meta

• Duplicate?
• What rules should I add?
• Are my explanations sufficient?
• Any room for improvement?

It's possible to "factor" any invertible (a.k.a. non-singular) square matrix A into a combination of a permutation matrix1 (P), a unit3 lower triangular matrix2 (L), a diagonal matrix4 (D), and a unit upper triangular matrix2 (U).

That is, A = PLDU

For instance, the matrix [[4, 5], [2, 3]] can be expressed as the multiplication of the following matrices:

P = [[0, 1],
[1, 0]]
L = [[1, 0],
[2, 1]]
D = [[2, 0 ],
[0, -1]]
U = [[1, 3/2],
[0, 1  ]]


Given an invertible square matrix A, output P, L, D, and U.

# Test Cases

TBD


# Rules

• Any reasonable output format is acceptable, but P, L, D, and U must be separate outputs.

1. A permutation matrix is a permutation of the identity matrix.

2. An upper triangular matrix is a square matrix whose nonzero values occur only on or above the main diagonal, and a lower triangular matrix is a matrix whose nonzero values occur only on or below the main diagonal.

3. A unit triangular matrix is a triangular matrix whose main diagonal is all 1s.

4. A diagonal matrix is a matrix whose nonzero values occur only on the main diagonal.

# Become a Word-Pontif

The french used to define the word pontif as one who builds bridges stemming from the conjunction of pons, facere which literally translates to a bridge, to create one. Your task will be, given a list of 1 or more lower-case words l (String Array), output the MAXIMUM length of a bridge that can be built from these words.

# Bridge Rules

• Bridges can be made by connecting two or more words together:
• Words must be connected prefix-to-suffix or suffix-to-prefix.
• To join two words into one:
• The suffix of the first must match the prefix of the second (abc+cba=abcba).
• The prefix of the first must match the suffix of the second (earl+toe=toearl).
• If a word's prefix/suffix contains more than one common character:
• You can only connect them with the maximal common substring.
• In other words,abc and bcdefg can be connected using a[bc]defg.
• The length of a bridge is simply the length of the conjoined words in characters.

# Building Material Rules

• The list will contain at fewest 1 word.
• The list may hold 0 links between words, in this case the maximal size is the longest word in the list.
• The list will not contain the empty string and will only use the lowercase alphabet (a-z).
• The list MAY NOT contain duplicates.

# Examples

Example 1:

[abcdefgh,holographic,graphical,quine,loitering]

abcdefholo[graphic]al = 19

19


Example 2:

[noon,moon,loon,noon,groom]

groo[m]oon

8


Example 3:

[spoon,whatifgodwereoneofus,oneofusisatraitor,aaaaaaaaaaaaaa,aaaaaaaaaa]

whatifgodwere[oneofus]isatraitor (because the two aaaaa's overlap too much).

30


Example 4:

[abc,def,ghi,jkl,mnop,qrst,uvwxyz]

uvwxyz (No matches)

6


Example 5:

[xox,xxox,lol,lolol,lololol,xoxx]

xo[xx]o[x]ox    < 8  (Maximal of the xox path)
[lol]o[l]ololol < 10 (Maximal of the lol path)

10


Example 6 (Base):

[hi]

hi

2


Example 7:

# Note, when a link has been used it cannot be used twice.
# In other words, the brackets used cannot overlap in these examples.
[aa,aaa,aaaa]

aa[aa][a]a (Chose to use aaaa,aaa,aa)

7


# General Rules

• 1. This is extremely close to codegolf.stackexchange.com/q/132561/194 . 2. Examples 5 and 7 look wrong. – Peter Taylor Sep 12 '17 at 8:52
• In example 1, isn't it abcdefgholographicaloitering = 28? – KSmarts Sep 18 '17 at 14:22

# Word Grid Pathfinding

A follow up to Generating Word Grids and Validating Words in Word Grids.

## Meta

My original idea for this was to have entries compete, but I'd like to have different winning conditions. Given grid x, pit all scripts against each other for the following win criteria:

• Highest Score
• Shortest Path
• Fewest remaining tiles
• Longest Words

but I think perhaps just making it code golf and offering a bounty to each of the criteria above after some time. I'd like some feedback on this. I like @LegionMammal978's idea, but feel like perhaps that could be a separate challenge (again, only if these are interesting to anyone!)

Given a grid of letters, complete a path of words that reaches from the centre of the board, to the edges. You must return lists of your moves as co-ordinates and your score will be tallied. As soon as there is a clear path from the centre to the edge, the game is over, and no further words will be scored.

## Details

Grids will always have an equal, odd, number of rows and columns, such that no direction contains fewer tiles.

## Restrictions

In the event that the grid is unsolvable (or becomes unasolvable because of your chosen path, you may return something falsy instead of a list of co-ordinates.

Your script must be able to handle grids of varying sizes and solve them in a reasonable time, such that a service like TIO can be used, without causing problems in most cases, for extremely large inputs (> 500). You are free to take input in any reasonable format, but please include a link to your script with a wrapper such that it can take input in via STDIN/script arguments via an online service.

#TODO: copy details of the adjacency rules from above.

For example, in the grid provided below, the J, I, P or O letters (north, east, south and west of the blank square) must be included, once this word has been removed, you have more available words.

There are bonus letters that provide a double point score, denoted by a lowercase letter or ! (instead of ? for a blank tile). Blank tiles are used exactly as they are in Scrabble and can count as any letter, the validating program will search for words replacing the ? (or !) with a wildcard. Letters are scored as per Scrabble:

0 points: blank tiles
1 point: E, A, I, O, N, R, T, L, S, U
2 points: D, G
3 points: B, C, M, P
4 points: F, H, V, W, Y
5 points: K
8 points: J, X
10 points: Q, Z


Your score will be calculated by the validator.

## Examples

Input:

UWDESTKP?
TERMDYTSR
ROANJLEFT
EkCI OOsT
IPAJPGMNY
MZLORITVI
GwEGgPUeI
MNROYOEER


Output:

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


Total moves: 2
Points: 21

#TODO: more examples.

# Shift-left golfer

Sometimes when doing code-golf, a person needs to understand which format is shorter:

• 2147483648
• 0x80000000
• 1<<31

You will receive a number in one of the three formats above: decimal, hexadecimal, or shift-left operation. If there is no advantage in converting it to another format, just leave the number the way it is; otherwise I want the shortest format. Of course there are numbers you can't convert to shift-left format!

# Notation:

• Hexadecimal0x#######.... where there are no leading zeros after the x. When accounting for evaluating the golfiness, the 0x part is also taken into consideration. For example 0x80000000 has a length of 10.

• Decimal#######.... where there are no leading zeros.

• Shift-left#...<<#.... no leading zeros both sides of <<. The << operator is also considered for length, e.g 1<<31 has a length of 5. You must also handle multiple digits before the << signal.

# represents a digit and ... represent possible repetition of digits

I don't care if you handle leading zeros at the input or not; but if you handle them, you must do the comparison operations without them and output also without them — You're a golfer, come on! You will understand!

There will be no accepted answer.

, so I want to know shortest answer by language.

# UPDATE 1:

In spite of @dzaima 's comment, now it also needs to handle multiple digits before << signal.

• How about just take an integer as input and return the shortest form as output? – hyper-neutrino Sep 15 '17 at 19:20
• 1<<31 has a length of 4 not 5? – Rɪᴋᴇʀ Sep 15 '17 at 22:38
• @Riker: Sorry, my mistake. Now fixed. – sergiol Sep 15 '17 at 22:59
• @dzaima: Updated. Yes, it will need to handle multiple digits before << – sergiol Sep 16 '17 at 11:07
• If you allow non-ones in front of the byte shift as input, but not as output, an input like 99<<99 would result in the output having more bytes than the input. – Jonathan Frech Sep 18 '17 at 5:23
• What about something like 0x45<<0x378? i.e., why not hex numbers in left-shifts? – wastl Jul 7 '18 at 20:38

# Translate Tetris moves to GoL!

Unless you've been living under a rock, you're probably aware of the fact that the highest voted unanswered, incredibly hard challenge to build a working game of Tetris in Conway's Game of Life just recently got answered. (Go check it out if you haven't already.)

Unfortunately, since this game is written in Conway's Game of Life, giving input to the code is a bit tricky. (Of course, if they can simulate Tetris in GoL, you can play it with tricky moves. :P) To quote the main answer:

Each move only requires editing a single bit of RAM, and this input register is automatically cleared after the input event has been read.

Each Tetris move corresponds to a single number by the following table:

value     motion

1         counterclockwise rotation
2         left
4         down (soft drop)
8         right
16        clockwise rotation


Now, of course, if there was only a way to automate this...

## Challenge

Write a program/function that takes a series of keypresses as input and outputs each keypress' respective number according to the table above.

The keypresses should map as the following:

value            motion

<                counterclockwise rotation
<left arrow>     left
<down arrow>     down (soft drop)
<right arrow>    right
>                clockwise rotation


### Specifications

• Standard I/O rules apply.
• Standard loopholes are forbidden.
• This challenge is not about finding the shortest approach in all languages, rather, it is about finding the shortest approach in each language.
• Your code will be scored in bytes, usually in the encoding UTF-8, unless specified otherwise.
• Built-in functions that perform this task are allowed but including a solution that doesn't rely on a built-in is encouraged. (Pshh, how likely is that?)
• Explanations, even for "practical" languages, are encouraged.

### Test cases

// incoming


# Sandbox

• Should I switch from keypresses to strings of ( < v > )?
• I'm really lacking on tags...
• Bump!
• Not all languages can support keypresses, so using a string would be better. – fireflame241 Sep 23 '17 at 18:20
• Also, if you go for keypresses: What happens if I hold a key for 10s? What happens if I hold a key and simultaneously press another one? – ბიმო Sep 25 '17 at 11:04

# Two-Symbol n-state Universal Turing Machine

A program is defined as a set of transition rules from one state to another based on the current state and symbol, optionally moving the tape head left or right.

The goal is to produce a program that satisfies all of the following criteria:

• It is a two-symbol Turing Machine program.
• It emulates a two-symbol Turing Machine program that is represented on the tape.
• where all tape that is not data is initialised to one symbol (designated 0 - the other is 1).

There are two scoring criteria:

1. The number of states. Smaller is better.
2. The compressibility of the program format (see below).

There is an individual scoring for each criterion and a combined position. The combined position is the sum of the ordinal positions in the leaderboard for each criterion (e.g. if your solution is 1st for number of states but 4th for compressibility it has a combined position of 5th). In the likely event of a tie, the compressibility of the program format is the tie-breaker.

## Compressibility of the Program Format

The compressibility of the program format is defined as the number of (additional) states required to write the program onto a blank (0) tape, move the head to the start position of the program and start running the emulator on the program (change state to a correct emulator state). Sandbox note: Hand-compressed test-cases? Average-case Big O?

• Todo: Work in a reference to this article and how a good solution to this challenge will reduce the upper bound for the maximum computable value of the Busy Beaver function. – wizzwizz4 Sep 22 '17 at 20:49
• Is there a way to tell the Kolmogorov complexity when compressed through a certain method? It seems like the compressibility of the input format is poorly defined and will vary between inputs. – wizzwizz4 Sep 22 '17 at 20:54
• I'm not quite seeing the busy beaver connection. Clearly it's not about emulating a single program, because in general the program itself would have fewer states than the program which puts it onto the tape and then runs the emulator; so it must be about some kind of loop over all programs, but then you run into undecidability of the termination of the emulator programs, meaning that the emulator certainly doesn't terminate. – Peter Taylor Sep 23 '17 at 20:25

# It’s raining numbers! Better to get a good umbrella!

Your task is to take in one integer input and print a “raining” alternating pattern with that number, and an umbrella of appropriate size to protect yourself from such a rain!

# Examples

1 =>

1
_|_
/   \
-----
|
C

2 =>

2
2
___|___
/       \
---------
|
|
C

3 =>

3       3
3
3       3
_____|_____
/           \
-------------
|
|
|
C

4 =>

4       4
4       4
4       4
4       4
_______|_______
/               \
-----------------
|
|
|
|
C

10 =>

1       1       1       1       1
0       0       0       0       0
1       1       1       1       1
0       0       0       0       0
1       1       1       1       1
0       0       0       0       0
1       1       1       1       1
0       0       0       0       0
1       1       1       1       1
0       0       0       0       0
1       1       1       1       1
0       0       0       0       0
1       1       1       1       1
0       0       0       0       0
1       1       1       1       1
0       0       0       0       0
1       1       1       1       1
0       0       0       0       0
1       1       1       1       1
0       0       0       0       0
___________________|___________________
/                                       \
-----------------------------------------
|
|
|
|
|
|
|
|
|
|
C


# Rules

• The output should use only the ascii characters _ | - / \ C, space, and the digits (no tabs are allowed).
• Numbers should have an alternating pattern, two digits on the same line are separated by 7 spaces.
• Number with more than one digit must be written vertically.
• The size of the first line of the top of the umbrella should be equal to 4n-1, for input n, centered below the “rain”; the size of the second line should be equal to 4n+1.
• The shank of the umbrella under the top is centered and should be of height n (the | characters), and terminated by a C handle.
• Lines can have trailing spaces.

This is a task, so the shortest solution is any language wins.

• shortest solution in any – Adám Sep 27 '17 at 7:36
• I think that you should explicitly state the input for each example output. – H.PWiz Sep 27 '17 at 9:21
• Allowed whitespace should be mentioned in the first rule. Regular spaces seem obvious, but using tab characters in place of 4 spaces could be used and it's a good idea to explicitly allow or forbid it. Also, that rule should start with "The output should..." to clarify that this is not restricted-source – Kamil Drakari Sep 27 '17 at 14:46

# Sort a nested object by nested value

Your goal is to sort a nested object by a nested value. What does that mean? For example:

#1: Input

{
foo: {
category: "A",
hello: "world",
color: "blue"
},
bar: {
category: "B",
cu: "cumber",
color: "blue"
},
baz: {
category: "A",
let: "tuce",
color: "green",
}
}


#1a: Output sorted by category

{
A: {
foo: {
hello: "world",
color: "blue",
},
baz: {
let: "tuce",
color: "green"
}
},
B: {
bar: {
cu: "cumber",
color: "blue"
}
}
}


#1b: Output sorted by color

{
blue: {
foo: {
hello: "world",
category: "A"
},
bar: {
cu: "cumber",
category: "B"
}
},
green: {
baz: {
let: "tuce",
category: "A"
}
}
}


Note that the sorting key is always deleted from the objects (when sorting by color none of the items contain color).

Given an object, and a sorting key (a string), output the sorted object as shown.

## Rules

• You can always assume that the value of the sorting key is a string (as it also needs to be a key in the output)
• You can always assume that the given sorting key exists in all values
• Sorting will only occur on the first-level objects, but the sorting key can be nested (see test case #2)
• The object may be a JSON object, a python dict, a JS object, etc. but must always have string only keys.
• You may accept the object as a JSON string and/or return a JSON string.

## Test Cases

#2: Input

Sort by: rating.healthiness

{
icecream: {
sweet: true,
rating: {
tastiness: "8",
healthiness: "4"
}
},
pizza: {
sweet: false,
rating: {
tastiness: "9",
healthiness: "3"
}
},
chocolatecake: {
sweet: true,
rating: {
tastiness: "8",
healthiness: "3"
}
}
}


#2: Output (sorted by rating.healthiness)

{
"3": {
pizza: {
sweet: false,
rating: {
tastiness: "9"
}
},
chocolatecake: {
sweet: true,
rating: {
tastiness: "8"
}
}

},
"4": {
icecream: {
sweet: true,
rating: {
tastiness: "8"
}
}
},
}


## Sandbox Questions

1. I really need to make the question clearer. Any thoughts? How can I better describe the task?
2. Is this a duplicate?
3. I'm guessing I need a better title. Any ideas?
4. Should I make the input a JSON object or just a general object?
5. Are multi-level nested objects even possible? Would it be too easy without them?
6. Should I also allow booleans & numbers as the value for the sorting key (and then in a key form it would be stringified)?

# Output the Yggdrasil graph

In Norse mythology, Yggdrasil, or the world tree, is a giant tree that spans the entire universe and connects all nine worlds of the Norse mythology together. Here, we shall take a rather liberal reinterpretation of the term "world tree" - it's the tree that contains all other trees as subgraphs. Not only that, but each graph is present everywhere in Yggdrasil. Clearly, the only way to achieve that is if every node in the graph has infinitely many neighbors.

Yggdrasil is the unique (up to isomorphism) non-empty graph with the two properties that each vertex has ℵ₀ neighbors and that there is a unique simple path between any two vertices. In other words, Yggdrasil is the Cayley graph of the free group with countably infinitely many generators. Your goal is to output this graph.

Nodes can be given any printable label of your choice, as long as they are non-empty and unique within the graph. Edges shall be denoted as pairs of vertices in either order. It must be clear from the output which are the two nodes in a graph (a-b-c is not an acceptable representation of an edge from a-b to c, but ["a-b", "c"] is fine). In the output, each edge shall be output on a single line, and different edges shall go on different lines.

The output should be just the list of edges in the graph, one edge per line. Each edge in the graph must be output exactly once, and in a finite amount of time (barring memory limitations). Edges not in the graph must not be output. For example:

• Listing the edges in breath-first order is not sufficient, as any edge disjoint from the root would not get output.
• Listing the edges in depth-first order is not sufficient, as no more than two edges of any node would ever get output.
• It is sufficient (but not necessarily optimal) to generate the output by repeating (for each node in a copy of the list of known nodes, take the first unknown child, output the edge to it and add it to the list of known nodes).

The sufficient example above will output, if nodes are labeled 0, 0 1, 0 2, 0 1 1, ... :

0 => 0 1
0 => 0 2
0 1 => 0 1 1
0 => 0 3
0 1 => 0 1 2
0 2 => 0 2 1
0 1 1 => 0 1 1 1
...

• So basically we have a countably infinite set of vertices V, a countably infinite index set I, and an injection (V x I) -> V. Since any bijection is an injection, we can use minor variants of e.g. codegolf.stackexchange.com/q/8892/194 , codegolf.stackexchange.com/q/78606/194 , codegolf.stackexchange.com/q/48705/194 with a loop for(n=0;;n++) wrapped round to create a valid answer. So although quite well disguised this is actually a dupe. – Peter Taylor Oct 3 '17 at 8:34
• @PeterTaylor not sure how that would work. Are you trying to output the complete infinite graph rather than the infinite order regular tree? – John Dvorak Oct 3 '17 at 9:00
• Use the reverse direction of the bijection: N -> (N x N). Then for(n=0;;n++)print(unpair(n)[0],"=>",n). Every node has an infinite number of successors, but each node has only one predecessor, so it's a tree. For the previous questions which use a bijection N -> (Z x Z) it's ever so slightly more subtle: to enumerate the entire tree we need to add in a bijection N -> Z and write for(n=0;;n++)print(unpair(n)[0],"=>",z(n)), but there are some very simple bijections N -> Z. – Peter Taylor Oct 3 '17 at 9:28

# Is my Sukkah Kosher?

Do not rely on this text for questions of Jewish law!

You will be given a floor plan of a sukkah as follows:

• A rectangular 2D text (in any reasonable format).
• The first and last rows and columns will consist of printable ASCII (32-126).
• All interior characters will be spaces.

Determine if the sukkah is acceptible according to these simplified rules, using the scale of one character width/height representing the tefach unit.

• The inner area, as encompassed by the completion of the two longest solid walls into a square, must be at least 6 units by 6 units.

• If the two longest solid walls are across from each other, then the shorter one must be at least 6 units long, and the length with with they are diametrically across from each other must also be 6 units long.

• There must be an additional wall which is at least one unit long.

• The walls may be made of any material, i.e. any character except space.

• Walls with single unit gaps are still considered solid.

You may answer with any two distinct values, but please specify if different from true/1 and false/0. Explanations are appreciated.

### Acceptable

oOOOo.ooo...o--o
#              @
#              )
#              (
#
|
#
+++++++*******


oOOOo.ooo...o--o

@
@
@

+++++****



o O o o o . o

@

@
@

+++++****


### Not acceptable

oOOOo.ooo...o--o
#              @
#              )
(

|
#
++++      ****


       oOOOo.ooo..

@
@
@

+++++****



o O o o o . o

@

@
@
8
8


## A Conc-urn-ing Problem

You have a mysterious urn, which contains 0 <= n <= 10 sets of k balls. Each set of balls shares a numeric label, from zero to n-1. You perform a repeated experiment, wherein you remove a ball from the urn, and note its number. If the number of balls in the urn with the same label as the ball you removed has the highest or tied for highest frequency still in the urn, you put the ball back in.

Taking the recorded results of each of the trials yields an infinite sequence. For example, you might have for n=2, k=2 pulled: 1001000000...

Given n and k write a program or function that returns a regular expression which will match any valid real number generated by this process, and which fails to match any other real number.

### Sandbox

This is missing quite a bit (haven't written a program yet), but I'm not sure if it is too tedious the way that it currently is. It's somewhat boring if restricted to n=2 but rather quickly becomes tedious after that. Since most of the result would be symmetric, would it make sense to only require the "first" result? This also seems like it removes too much of the interest in the problem.

# Search Stack Overflow for Duplicates

The Stack Overflow search algorithm has been under fire recently. Several problems with the search algorithm being flawed exist, but one of the most important issues raised is with duplicates:

[...] The search engine is used while authoring a question to find potential duplicates. At that point there is no way for you to take advantage of its features through custom search operators, and it absolutely, positively must be as good as an external search engine in this scenario. Unfortunately, it isn't. – IInspectable (source)

A flawed duplicate search algorithm causes a lot more work for the comparatively few reviewers and duplicate closers than there should be, by not informing the question askers that the question that they are attempting to post is a duplicate. It is also bad for the question askers, preventing them from finding the answer to their question until somebody reviews the question.

This is where you come in. Given the title, body and tags of a question, output a list of 25 relevant questions in a reasonable format (e.g. question ids). Your program should run within 500ms on the Stack Exchange servers for each question. (Sandbox note: How fast are the Stack Exchange servers? What conversion factor should I use to test on my hardware?) You have access to all T-SQL database tables available from the Stack Exchange Data Explorer, but the current question that needs to be checked for duplicates will be absent from all tables (so it isn't found as a duplicate of itself). To test the algorithm, it would be tested on a random selection of or all of the existing duplicates on Stack Overflow - the algorithm with the lowest average position of the duplicate master(s) in the list would win, where "not in the list" is counted as 50. The set of existing duplicates tested would be the same for all algorithms to test - rationale includes scoring of questions with multiple duplicate masters. The search algorithm should be deterministic. It is allowed to prepare a cache table beforehand - none of the duplicates to test will be passed to this part of the algorithm. This cache table should be able to be updated with new questions without being completely rebuilt. (Sandbox note: How to score this?)

(Sandbox note: The final paragraph should be spread out and better laid out and reworded, but I think the wall of text contains enough information.)

# Constructively golf true primes!

## Introduction

A recurring pattern that I see in challenge involving primes is the (over-) use of prime-checking built-ins and of factorization built-ins. However, I kinda don't trust especially the latter, which is why today, we're gonna build primes and include a certificate that the result is actually a prime.

## Input

A positive integer n denoting the length of the resultung prime in a basis of your choice.

## Output

A list of primes in the base you picked above, one of these primes is of length n and one of these primes is smaller than 20.

## What to do?

Your challenge is to generate a prime of length n of which the primality can be reduced to the primality of one of the following primes: [2,3,5,7,11,13,17,19]. This can be achieved using Pocklington's criterion. Now the idea is to chain up from any of these primes using said criterion to a prime of appropriate size, while also outputting the intermediate steps so primality can be checked easily.

For your convenience, I shall reproduce the relevant theorem here:

Let N>1 be an integer and suppose there exist a,q such that

• q is prime
• q divides N-1
• q>sqrt(N)-1
• a^(N-1) mod N == 1
• gcd(a^((N-1)/q)-1,N)=1

Then N is prime.

And as you might see, your initial set of primes (as candidates for q) is limited to the above short list of primes smaller than 20.

## Who wins?

This is so the shortest solution in bytes wins!
However this is also so all solutions must run in (expected) polynomial time in n. Standard IO and Loophole rules apply.

## Got any help?

If you need algorithmic help, I suggest you consult the Handbook of Applied Cryptography, chapter 4 (PDF), algorithm 4.62 (on page 153 or 22 in the PDF) or you independently look for Maurer's prime generation algorithm (originally published here).

# I got them Mad Matrix Moves

Given a list of edges representing a simple directed graph and (optionally) the number of vertices n>1, output the adjacency matrix of that graph.

The vertices will always be numbered consecutively starting at 0 (or 1 -- your choice).

The adjacency matrix is defined as the n by n square matrix M such that M[i][j] is 1 if there is an edge from vertex i to vertex j and 0 otherwise.

# Example

For this example and the test cases, we will have the vertices numbered starting at 1.

Let's use the sample input [(1,2),(1,3),(3,2)]. Since there are vertices numbered 1-3, n=3 and our output is a 3 x 3 matrix.

The output should be

[[0, 1, 1],    <= (1,1) doesn't exist in the input list, (1,2) does, (1,3) does.
[0, 0, 0],    <= (2,1) doesn't exist, same with (2,2) and (2,3)
[0, 1, 0]]    <= (3,1) doesn't exist, (3,2) does, and (3,3) doesn't


(concisely represented as [[0,1,1],[0,0,0],[0,1,0]] in test cases).

# Notes

• Every vertex is the start and/or end of at least one edge.
• You may replace 1 and 0 in the output with any two consistent distinct values of your choosing.
• The input graph is simple, meaning that it has no loops nor multiple edges (e.g. no edge [1,1] or graph [[1,2],[1,2]])
• The graph is directed, meaning that each edge has a start and an edge (e.g. the edge [1,2] is distinct from [2,1])
• Every vertex is an endpoint of at least one edge
• This is , so shortest code in byes in each language wins.

# Test Cases

One test case per line. Each test case is in the format edges, n => output.

[(1,2)], 2 => [[0,1],[0,0]]
[(2,1)], 2 => [[0,0],[1,0]]
[(1,2),(2,1)], 2 => [[0,1],[1,0]]
[(1,2),(1,3),(3,2)], 3 => [[0,1,1],[0,0,0],[0,1,0]]
[(1,2),(2,3),(3,4),(4,5)], 5 => [[0,1,0,0,0],[0,0,1,0,0],[0,0,0,1,0],[0,0,0,0,1],[0,0,0,0,0]]
[(1,2),(3,4),(4,3),(2,1),(2,4),(4,2)], 4 => [[0,1,0,0],[1,0,0,1],[0,0,0,1],[0,1,1,0]]
[(1,2),(2,3),(3,4),(4,5),(2,1),(3,2),(4,3),(5,4)], 5 => [[0,1,0,0,0],[1,0,1,0,0],[0,1,0,1,0],[0,0,1,0,1],[0,0,0,1,0]]
[(1,2),(3,1),(2,3),(1,1),(2,1)], 3 => [[1,1,0],[1,0,1],[1,0,0]]
[(1,2),(3,2),(1,3),(5,4),(5,6),(5,1),(2,3),(1,5),(5,2),(3,6),(4,5),(5,3),(2,1),(3,5),(4,6),(6,3),(6,5),(4,2),(3,4)], 6 => [[0,1,1,0,1,0],[1,0,1,0,0,0],[0,1,0,1,1,1],[0,1,0,0,1,1],[1,1,1,1,0,1],[0,0,1,0,1,0]]


# Get the Average Number of Bytes for an Answer

Have you ever wanted to know the average number of bytes all the answers to a given code golf question took? Probably not. But I did!

## Input

You'll have to take in a link to a codegolf exchange question by text or you can run this in a browser extension/user-script. If you have a clever way of identifying the webpage and producing the necessary output, just ask about it in the comments, and I'll update the question as long as it doesn't violate the rules. The input will be a link to a codegolf question. It will include http::// or https:://. The slashes will be facing this way: "/". The link may not be to a code-golf challenge specifically, but it could be something like a code-challenge.

## Output

If the user inputs something that isn't to a code golf website output something along the lines of "Hey! That's not a link to a code-golf challenge" If the user inputs a link that links to the codegolf exchange, but isn't a codegolf (maybe it's a code-challenge) the program should output anything that is not a natural number.

If there are strikethroughs through previous amounts of bytes a solution took, those should not be included in the average. If the person answering the question in one of the links did not conform to formatting standards, the program doesn't have to account for it. Minor differences will be allowed. Specifically, the number of bytes should be within 5 lines of the top of the answer and bolded.

All answers should be rounded to the nearest whole number with .5 rounding up.

## Examples

Input:

https://codegolf.stackexchange.com/questions/54038/average-out-two-lists

Output:

95

## Winning Criterion

The winner will be given by (1 / execution time (s) + bytes).

If you know of anything that I missed, comment below.

• What if I make the output message my entire program and then just exec it? – hyper-neutrino Oct 10 '17 at 23:30
• @HyperNeutrino I'm not really sure what that means. If it takes a link in and outputs the answer then you've completed the challenge. If it outputs the answer and 20 lines of unnecessary information that the user can see, I would say that that doesn't pass the program. – Byte11 Oct 10 '17 at 23:34
• My point is, what if I make a string containing my entire program, use string slicing to output a good falsy message, and then use exec to run the string? Would I be exempted from counting the bytes of my string? – hyper-neutrino Oct 11 '17 at 0:05
• @HyperNeutrino That's a smart way to get around the rules. No, you wouldn't be exempt from the rules, but from a literal interpretation, you could argue that that is allowed. How should most concisely update my rules to prevent this? – Byte11 Oct 11 '17 at 0:08
• I'd just guarantee that the input will follow a specific format, because making the input contain backslashes, missing components, etc. is just a pain and doesn't demonstrate the answerer's ability to actually do what you really want. Essentially, don't add too much fancy stuff – hyper-neutrino Oct 11 '17 at 0:22
• @HyperNeutrino Okay, I've updated the question. – Byte11 Oct 11 '17 at 0:47
• along the lines of  → unclear what you're asking. – user202729 Nov 3 '17 at 13:21
• Also what exactly is the winning criteria? Another point: A link to this site never have https:://, only https://. – user202729 Nov 3 '17 at 13:21

# Optimised Hashing

For a given set of input, output a program that can 'hash' the input with a minimum number of collisions.

## The Challenge

Write a method or function that receives an array of Strings (see input for more detail) and outputs a full program. This program must, for each String in the original input array, print to STDOUT (or equivalent) some positive integer i where i<100 and is unique for that input.

## The Input

Each program will be tested with 4 different input sets of 50 unique Strings;

• 50 English words of the same length.
• 50 English words of differing lengths.
• 50 randomly generated character strings of the same length
• 50 randomly generated character strings of differing lengths

All Strings in all inputs will only contain the character set [a-zA-z] (ASCII values 65-90 and 97-122) and will all be no more than 20 characters long.

## Special Rules

• Standard loopholes are forbidden.
• Inbuilt hashing functions are not allowed.
• You must provide a free and easily accessible environment to compile and run both programs with your answer.
• I reserve the right to discount any program which takes more than 10 minutes to complete any test.

## Scoring

You will be scored by combining the following;

• The byte count of your original program
• The byte count of each outputted program
• 5 penalty points for each 'collision'.

I will keep and update a leader board as programs are added and I can test them.

Please let me know if I've missed anything; this is my first question idea!

# Hunting The Wren

Write a program to produce the words to the folk song Hunting The Wren.

"We're hunting the wren." says Robin to Bobbin.
"We're hunting the wren." says Richard to Robin.
"We're hunting the wren." says Jack of the land.
"We're hunting the wren." says everyone.

"Where oh where?" says Robin to Bobbin.
"Where oh where?" says Richard to Robin.
"Where oh where?" says Jack of the land.
"Where oh where?" says everyone.


The song continues with the same structure.

"In yonder green bush."
"How get him down?"
"With sticks and stones."
"How get him home?"
"The brewer's big cart."
"How will we eat him?"
"With knives and forks."
"Who'll come to the dinner?"
"The King and the Queen."


The song concludes with three more verses, which because they have no repetition, we'll omit for the purposes of this challenge.

Rules

• The program must produce the full words of the song as 54 or 55 lines of text.
• Each verse of four lines must be separated by a blank line. A blank line on the end is optional.
• You must not use a text decompression library. (GZIP the whole song is 380 bytes.)
• Normal code golf rules apply. Shortest code wins.

C# Reference Implementation

public class Program
{
public static void Main()
{
string[] starts = new [] {
"We're hunting the wren.",
"Where oh where?",            "In yonder green bush.",
"How get him down?",          "With sticks and stones.",
"How get him home?",          "The brewer's big cart.",
"How will we eat him?",       "With knives and forks.",
"Who'll come to the dinner?", "The King and the Queen." };

string[] ends = new [] {
"says Robin to Bobbin.",      "says Richard to Robin.",
"says Jack of the land.",     "says everyone."            };

foreach (string start in starts)
{
foreach (string end in ends)
{
System.Console.WriteLine("\"" + start + "\" " + end);
}
System.Console.WriteLine();
}
}
}


# Pokémon Champion

This challenge is about writing the ultimate bot for battling Pokémon. Since knowledge of competitive Pokémon battling is necessary, I'll leave that to the experts at Smogon University.

### Rules

• Your bot must battle another bot in a Gen 7 Random Battle Format.
• Your bot will be judged based on its performance in a round-robin tournament orchestrated by the author of the challenge, against all other submitted bots before a specific deadline.
• In order to avoid reinventing the wheel, there are several frameworks already available to choose from. Unfortunately, a lot of these are written in Node.js, so you might still have some porting to do, unless this challenge decides to create its own framework for battling.
• Since your bot will be connecting to a Showdown server using the existing Web Socket API, any error in your program that causes the bot to become non-responsive or to disconnect will automatically forfeit that match.
• Standard loopholes apply, and do not exploit any possible bugs in the API. If you find a bug, please report it here.

### Further Considerations

While in theory, I think this would be a great idea, I believe this would require a lot of time-investment and groundwork, which frankly I don't have the availability for right now, so anyone is free to take this over, but please be courteous and get my consent in The Nineteenth Byte first. Just @PatrickRoberts and wait for a reply before modifying this proposal.

* Not sure if it's preferable to write an API specifically for this challenge to eliminate the need for Web Socket communication, since there are already available platforms. The idea is to host an official tournament at a certain date (yet undecided) on Pokémon Showdown.

• I could use a new bot on my side server (the one I've got doesn't know about Z-moves so even I can beat it at Ultimate Z...) – Neil Oct 18 '17 at 0:19

# All the same digits

For any two coprime integers n, b > 1 there exist infinitely many integers k > 0 for which n * k's representation in base b only contains the digit b-1.
This challenge's task is to output the smallest such k for given integers n, b.

### Input

Two integers n, b with the above described properties in any reasonable format (integers, strings, ...). If your language does not support arbitrary precision integers, you can assume that n, b < 2**31.

### Ouput

An integer k with the above described properties in any reasonable format (integer, string, ...). If your language does not support arbitrary precision integers, you can assume that k < 2**31.

### Test cases

f(  n,     b) == k

f(  7,    10) == 142857
f(  13,    5) == 48
f(  14,   13) == 12
f(1728, 1729) == 1
f( 107,   99) == 54863250648363053681585635237627534906401818527472898624219397466199311510764517134614152141940101983414


To generate more test cases, take a look at my reference implementation written in Python 2.

Fraction periods can also be used to calculate k (example given for n, b = 13, 10).

1/13             =      0.076923(076923)* (period length 6)
1/13 *  10**6    = 076923.076923(076923)*
1/13 * (10**6-1) = 076923
999999   = 076923 * 13
k =  76923

• Not true. Consider n=b>1. You need a coprimality condition. – Peter Taylor Oct 17 '17 at 16:03
• @PeterTaylor Thanks for noting. – Jonathan Frech Oct 17 '17 at 17:38

I'm posting this on sandbox first, because this might not be a good challenge for this site, or just too complicated, because it's about constructing a meaningful sentence. Please, tell me, if it's appropriate task for this site.

Also a note: If you want, I can wait for Christmas with this.

# Back to the New Year!

You encounter a probably hard challenge.

Inspired by this answer by @dansalmo.

If we sum character codes in the string Happy new year to you!, we will get 2014. With later years, people started to modify the string, so it fits the current year:

• 2015: A Happy New Year to You!
• 2016: Happy New Year to you!!!

## The challenge

Given an integer year, output a string meaning "Happy new year!". Sum of character codes should be equal to the integer.

Rules:

• No default loop holes allowed
• Output rules:
• Meaning rules:
• You must use the word Happy - you cannot use any other adjective instead.
• You must wish a NEW year, no matter if it's 2010 or 2020!
• You can only wish a happy new year - You can't wish a happy new Easter...
• You can target the string to a person or group, or to everybody: Happy new year!, Happy new year, Soaku!, Happy new year, CodeGolfers!
• You can add new words, but the sentence can't lose the meaning!
• Output must have valid grammar, but you can mess up the punctuation. Just note that you can't use punctuation characters except trailing exclamation marks.
• Letter case rules:
• First word must start with uppercase letter.
• Any other word can start with uppercase or lowercase.
• Letters that aren't first should be lowercase. The only exception is when all letters in the word are uppercase.
• Punctuation rules:
• You are not allowed to use any punctuation characters, except on the end of the string
• There must be exactly one or three exclamation marks ! at the end.
• Spacing rules:
• There must be exactly one space between words.
• No line breaks allowed
• Leading and trailing spaces/newlines are allowed, but they don't count in the character code sum. Word is the same as outputting Word.
• Character rules:
• You cannot use digits!
• You must only use ASCII letters (the only exception are the trailing exclamation marks)
• You can assume the input is an integer between 2000 and 3000

## Test cases

examples, don't need to be the same

2001 - Happy new YEAR to MYSELF!
2002 - A VERY HAPPY NEW YEAR TO PPCG!
2003 - Happy NEW Year TO MYSELF!!!
2004 - A happy new year to me!
2013 - A HAPPY NEW Year To The SE!!!
2014 - Happy new year to you!
2015 - A Happy New Year to You!
2016 - Happy New Year to you!!!
2030 - A Happy New Year To PPCG!!!


• I think meaning "Happy new year!" is too unclear. There is no way to objectively enforce this. – Wheat Wizard Oct 23 '17 at 17:38

# Behavior Driven Golfing

### Context

From wikipedia (emphasis mine): Behavior Driven Development (BDD) is largely facilitated through the use of a simple domain-specific language (DSL) using natural language constructs (e.g., English-like sentences) that can express the behavior and the expected outcomes.

Example in normal BDD (also from Wikipedia):

Story: Returns go to stock

As a store owner In order to keep track of stock I want to add items back to stock when they're returned.

### The challenge:

Write a program that reads like a single English-like sentence that executes the meaning of that sentence.

### Other details

• The program must receive input of some kind (stdin, arguments are okay depending on your language's syntax).
• The input can be limited in scope, (e.g. all real numbers, all positive even integers), but there must be infinitely many possible inputs assuming that your language doesn't have a cap.
• For example, if the input is an integer, you don't actually have to handle integers beyond the language's cap, if your language happens to cap at 32 bit long, it just has to be infinitely many in theory but not necessarily in practice.
• The program must have at least log(n) distinct outputs over an input space of size n.
• For example, if there existed a language where convert to zero was a valid program, returning 0 on all inputs would not be okay, but printing a number of 0 equal to the base 10 number of digits of the input number would be okay.
• The program should not error out on legal input.
• Irregular case and unicode characters are allowed
• Unicode characters will be interpreted as the similar character in English (so most commands in 05AB1E are allowed).
• Words may be delimited by punctuation marks instead of spaces, but they must be delimited.
• Punctuation should not be present in the middle of a word unless it's legal in English (such as an apostrophe in a contraction or a possessive)

Example valid answer for all requirements except the "must take input" requirement:

### HQ9+

Print Hello, world.

Since only the H character is an instruction in this language, all the other characters are ignored, and the program prints hello, world. Since case is ignored, this program does what the english sentence says it will do.

• As it's currently written, the task is way too broad. The task that the program should do must be narrowed and clearly specified (e.g., "add the input with itself") in order for this to be well-received. – AdmBorkBork Oct 20 '17 at 20:00
• I like the challenge, but I think it should be popularity-contest rather than code-golf. I just feel like code-golf will attract too many answers similar to the example: pick a language that ignores most characters, then write a sentence that describes a built-in and includes that built-in as the only executed character. Popularity Contest seems like it would attract much more interesting answers. – Kamil Drakari Oct 20 '17 at 21:59
• @KamilDrakari popularity-content is typically not well received, most of those are closed. – durron597 Oct 20 '17 at 23:20
• I'm not exactly sure how we can measure "X is a similar character to Y" objectively.. Probably @Kamil is right and this should be a popularity contest. – ბიმო Oct 26 '17 at 19:02
• @BruceForte, pop-con is not a "solution" to the problem that the spec is not objective. A pop-con should have an objective validity criterion and not be amenable to an objective scoring criterion. – Peter Taylor Oct 27 '17 at 12:04