# 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.

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

## 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]

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

# 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 – programmer5000 Aug 22 '17 at 22:05

# Where do I live? code-golfgeography*

Given a coordinate pair, supporting at least 2 decimal places (precision .01), determine the country containing that coordinate pair. The coordinate will be on land and will be at least ~0.5 degrees (~50 km Great Circle distance; thanks Peter Taylor!) from any border or coastline.

Input will be given as two decimal numbers in any reasonable format. Output should be the English name of the country according to this source; spaces, accents, non-alphanumeric characters, and capital letters are all optional. For countries like Iran, you can choose to output either "Iran" or "Islamic Republic of Iran". The same applies for all ...Republic... countries, like N/S Korea, Lao, Taiwan, etc. For Côte D'ivoire, you can choose to output either "Côte D'ivoire" or "Ivory Coast".

Exact built-ins are not allowed (ahem Mathematica). Online APIs are not allowed (ahem Google Maps).

Western and Southern coordinates can be given as a negative decimal or with W and S (you can also have N and E if wanted). Please specify your input format.

You will have to handle coordinates in Antarctica. Apparently it's a country now.

# Test Cases

Input           -> Output

37.42N,  94.88W -> United States of America
25.96N, 103.51W -> Mexico
9.39S,  59.39W -> Brazil
79.66S,  65.22E -> Antarctica
90.00S,  00.00E -> Antarctica # It's such a shame that 90N ?E/W is in the middle of the ocean
74.25N,  40.00W -> Greenland
63.08N,  15.34E -> Sweden
66.19N,  98.93E -> Russia
30.72N, 103.39E -> China
2.89S, 119.55E -> Indonesia
26.96S, 132.91E -> Australia


* not a real tag but I propose to add it

• Does "at least 0.5 degrees from any border or coastline" mean "at least 55.6km from any border or coastline" (i.e. great circle distance)? – Peter Taylor Sep 11 '17 at 8:34
• @PeterTaylor Yes, thanks for the calculation. I'll just say ~50 km, thanks. – HyperNeutrino Sep 11 '17 at 12:12

[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>
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 # Answer format # [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 • @Laikoni status-completed – programmer5000 Sep 11 '17 at 21:10 # 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 ]]  # Task 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 # Validating Words in Word Grids A follow on from Generating Word Grids Given a grid of letters and a set of co-ordinates, validate that the co-ordinates follow only cardinal direction changes, at least one of the co-ordinates touch an empty space in the centre of the grid, the resulting word is valid given the dictionary (taking into consideration any blank tiles) and return either the grid, with the letters at the co-ordinate removed along with the score of the word, or, if one of the conditions fails, the original grid and a score of -1. ## Details Please use the dictionary provided which is a /usr/bin/dict clone with all words converted to lowercase, non-alphabetic characters removed, and then de-duplicated. 0,0 will be the uppermost, leftmost character on the grid, working right and down. ## Scoring Letters are worth their values 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  Bonus tiles (indicated by a lowercase letter, or ! for a blank tile) provide a *2 multiplier and stack (eg. if my co-ordinates spell gOLf I would earn (((2+1+1+4)*2)*2), 32 points). ### Examples: Input: 6,4 6,5 5,5 4,5 3,5 3,6 2,6 1,6 UWDESTKP? ItDBaDEdI TERMDYTSR ROANJLEFT EkCI OOsT IPAJPGMNY MZLORITVI GwEGgPUeI MNROYOEER  Output: 9 UWDESTKP? ItDBaD dI TERMDY SR ROANJ FT EkCI OsT IPAJP MNY MZLO TVI GwEGgPUeI MNROYOEER  (spells RIGOLETE, (1+1+2+1+1+1+1)) Input: 0,3 0,4 0,5 0,6 UWDESTKP? ItDBaD dI TERMDY SR ROANJ FT EkCI OsT IP P MNY MZL TVI GwE gPUeI MNROYOEER  Output: -1 UWDESTKP? ItDBaD dI TERMDY SR ROANJ FT EkCI OsT IP P MNY MZL TVI GwE gPUeI MNROYOEER  (spells DEST which doesn't appear in the dictionary) Input: 5,6 4,6 4,7 4,8 UWDESTKP? ItDBaD dI TERMDY SR ROANJ FT EkCI OsT IP P MNY MZL TVI GwE gPUeI MNROYOEER  Output: 12 UWDESTKP? ItDBaD dI TERMDY SR ROANJ FT EkCI IP P NY MZL TVI GwE gPUeI MNROYOEER  (spells MOsT, (3+1+1+1)*2) ## Rules This is so the shortest code in bytes wins. • The order is not important, it can be score then grid, or vice versa. • Any reasonable format can be used for I/O assuming it is consistent. • All standard loopholes are forbidden. • This looks pretty good to me. – Rɪᴋᴇʀ Sep 15 '17 at 18:20 • Thanks @Pavel, I'll bear that in mind, i'm not sure how much interest there is based off of part 1, but I might still post this in the next week or so :) – Dom Hastings Sep 16 '17 at 9:21 # 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? ItDBaDEdI 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. # Proper Kerning Kerning is the adjustment of spacing between pairs of letters in order to obtain an aesthetic result. When kerning is applied automatically by a program (typically whatever editor you're using), it is said to be automatic. There are two types of automatic kerning. The one used in this challenge is metric kerning. With metric kerning, the amount of space between pairs of letters is dictated by the kerning tables found in the font file. Given a TrueType font file, output the kerning values for each mapping in the kerning table for ASCII characters 48 - 122 inclusive. ## Example calibri.ttf l="A" r="C" v="-15" l="A" r="G" v="-15" l="A" r="J" v="23" l="A" r="O" v="-23" l="A" r="Q" v="-23" l="A" r="T" v="-160" l="A" r="U" v="-32" l="A" r="V" v="-89" l="A" r="W" v="-80" l="A" r="Y" v="-150" l="A" r="t" v="-52" l="A" r="v" v="-38" l="A" r="y" v="-41" l="A" r="?" v="-68" l="B" r="A" v="-20" l="B" r="T" v="-48" l="B" r="V" v="-25" l="B" r="W" v="-24" l="B" r="X" v="-44" l="B" r="Y" v="-57" l="B" r="Z" v="-20" l="B" r="f" v="-20" l="B" r="t" v="-20" l="B" r="v" v="-20" l="B" r="x" v="-15" l="B" r="y" v="-20" l="C" r="G" v="-18" l="C" r="J" v="12" l="C" r="O" v="-18" l="C" r="Q" v="-18" l="C" r="T" v="10" l="D" r="A" v="-30" l="D" r="J" v="-22" l="D" r="T" v="-23" l="D" r="V" v="-24" l="D" r="W" v="-14" l="D" r="X" v="-31" l="D" r="Y" v="-39" l="D" r="Z" v="-22" l="E" r="A" v="-22" l="E" r="C" v="-24" l="E" r="G" v="-24" l="E" r="O" v="-32" l="E" r="Q" v="-32" l="E" r="S" v="-20" l="E" r="Z" v="-10" l="E" r="a" v="-34" l="E" r="c" v="-28" l="E" r="d" v="-30" l="E" r="e" v="-37" l="E" r="f" v="-64" l="E" r="o" v="-37" l="E" r="q" v="-30" l="E" r="t" v="-24" l="E" r="v" v="-48" l="E" r="w" v="-34" l="E" r="y" v="-48" l="F" r="A" v="-115" l="F" r="C" v="-18" l="F" r="G" v="-18" l="F" r="J" v="-109" l="F" r="O" v="-18" l="F" r="Q" v="-18" l="F" r="S" v="-29" l="F" r="X" v="-22" l="F" r="Z" v="-11" l="F" r="a" v="-55" l="F" r="c" v="-28" l="F" r="d" v="-20" l="F" r="e" v="-30" l="F" r="o" v="-28" l="F" r="q" v="-20" l="F" r="s" v="-35" l="G" r="T" v="-10" l="G" r="V" v="-10" l="G" r="W" v="-9" l="G" r="Y" v="-30" l="G" r="v" v="-29" l="G" r="w" v="-22" l="G" r="x" v="-14" l="G" r="y" v="-30" l="J" r="A" v="-35" l="J" r="X" v="-20" l="K" r="C" v="-78" l="K" r="G" v="-80" l="K" r="O" v="-97" l="K" r="Q" v="-97" l="K" r="S" v="-18" l="K" r="U" v="-29" l="K" r="W" v="-34" l="K" r="a" v="-34" l="K" r="c" v="-40" l="K" r="d" v="-33" l="K" r="e" v="-37" l="K" r="f" v="-25" l="K" r="m" v="-32" l="K" r="n" v="-32" l="K" r="o" v="-37" l="K" r="p" v="-32" l="K" r="q" v="-33" l="K" r="r" v="-32" l="K" r="s" v="-18" l="K" r="t" v="-38" l="K" r="u" v="-32" l="K" r="v" v="-101" l="K" r="w" v="-95" l="K" r="y" v="-85" l="L" r="C" v="-22" l="L" r="G" v="-47" l="L" r="J" v="25" l="L" r="O" v="-45" l="L" r="Q" v="-45" l="L" r="T" v="-150" l="L" r="U" v="-44" l="L" r="V" v="-147" l="L" r="W" v="-118" l="L" r="Y" v="-167" l="L" r="f" v="-23" l="L" r="t" v="-38" l="L" r="v" v="-78" l="L" r="w" v="-72" l="L" r="y" v="-79" l="O" r="A" v="-23" l="O" r="J" v="-27" l="O" r="T" v="-55" l="O" r="V" v="-25" l="O" r="W" v="-22" l="O" r="X" v="-64" l="O" r="Y" v="-55" l="O" r="Z" v="-38" l="O" r="x" v="-12" l="O" r="z" v="-10" l="P" r="A" v="-151" l="P" r="J" v="-140" l="P" r="T" v="-9" l="P" r="V" v="-10" l="P" r="X" v="-35" l="P" r="Y" v="-11" l="P" r="Z" v="-29" l="P" r="a" v="-44" l="P" r="c" v="-43" l="P" r="d" v="-34" l="P" r="e" v="-41" l="P" r="f" v="12" l="P" r="o" v="-41" l="P" r="q" v="-34" l="P" r="s" v="-32" l="P" r="t" v="12" l="P" r="y" v="12" l="Q" r="J" v="41" l="Q" r="T" v="-47" l="Q" r="V" v="-25" l="Q" r="W" v="-12" l="Q" r="X" v="12" l="Q" r="Y" v="-46" l="Q" r="g" v="59" l="Q" r="j" v="79" l="Q" r="x" v="31" l="Q" r=";" v="60" l="Q" r="]" v="32" l="R" r="C" v="-18" l="R" r="G" v="-19" l="R" r="O" v="-20" l="R" r="Q" v="-20" l="R" r="S" v="-27" l="R" r="T" v="-20" l="R" r="V" v="-28" l="R" r="W" v="-18" l="R" r="Y" v="-30" l="R" r="e" v="-36" l="R" r="o" v="-42" l="R" r="v" v="-26" l="R" r="w" v="-33" l="R" r="y" v="-33" l="S" r="A" v="-15" l="S" r="J" v="-9" l="S" r="T" v="-14" l="S" r="V" v="-14" l="S" r="W" v="-15" l="S" r="X" v="-13" l="S" r="Y" v="-20" l="S" r="v" v="-23" l="S" r="w" v="-17" l="S" r="y" v="-25" l="T" r="A" v="-160" l="T" r="C" v="-42" l="T" r="G" v="-59" l="T" r="J" v="-65" l="T" r="O" v="-58" l="T" r="Q" v="-58" l="T" r="S" v="-10" l="T" r="T" v="28" l="T" r="a" v="-160" l="T" r="c" v="-177" l="T" r="d" v="-147" l="T" r="e" v="-182" l="T" r="g" v="-151" l="T" r="m" v="-127" l="T" r="n" v="-127" l="T" r="o" v="-182" l="T" r="p" v="-127" l="T" r="q" v="-147" l="T" r="r" v="-127" l="T" r="s" v="-153" l="T" r="u" v="-127" l="T" r="v" v="-92" l="T" r="w" v="-86" l="T" r="x" v="-90" l="T" r="y" v="-93" l="T" r="z" v="-142" l="T" r=";" v="-114" l="T" r=":" v="-134" l="U" r="A" v="-45" l="U" r="J" v="-40" l="V" r="A" v="-96" l="V" r="C" v="-18" l="V" r="G" v="-25" l="V" r="J" v="-80" l="V" r="O" v="-27" l="V" r="Q" v="-27" l="V" r="S" v="-12" l="V" r="V" v="9" l="V" r="a" v="-114" l="V" r="c" v="-103" l="V" r="d" v="-87" l="V" r="e" v="-102" l="V" r="g" v="-100" l="V" r="m" v="-50" l="V" r="n" v="-50" l="V" r="o" v="-86" l="V" r="p" v="-50" l="V" r="q" v="-87" l="V" r="r" v="-50" l="V" r="s" v="-90" l="V" r="u" v="-50" l="V" r="y" v="-35" l="V" r="z" v="-82" l="V" r=";" v="-108" l="V" r=":" v="-73" l="W" r="A" v="-93" l="W" r="C" v="-22" l="W" r="G" v="-22" l="W" r="J" v="-88" l="W" r="O" v="-22" l="W" r="Q" v="-22" l="W" r="S" v="-10" l="W" r="X" v="-13" l="W" r="a" v="-71" l="W" r="c" v="-78" l="W" r="d" v="-72" l="W" r="e" v="-75" l="W" r="g" v="-54" l="W" r="m" v="-60" l="W" r="n" v="-60" l="W" r="o" v="-86" l="W" r="p" v="-60" l="W" r="q" v="-72" l="W" r="r" v="-60" l="W" r="s" v="-73" l="W" r="u" v="-60" l="W" r="v" v="-34" l="W" r="y" v="-53" l="W" r=";" v="-156" l="X" r="C" v="-57" l="X" r="G" v="-65" l="X" r="O" v="-57" l="X" r="Q" v="-57" l="X" r="S" v="-20" l="X" r="d" v="-44" l="X" r="e" v="-39" l="X" r="g" v="-9" l="X" r="o" v="-38" l="X" r="q" v="-44" l="X" r="t" v="-31" l="X" r="u" v="-38" l="X" r="v" v="-55" l="X" r="w" v="-49" l="X" r="y" v="-43" l="Y" r="A" v="-152" l="Y" r="C" v="-67" l="Y" r="G" v="-67" l="Y" r="J" v="-112" l="Y" r="O" v="-66" l="Y" r="Q" v="-66" l="Y" r="S" v="-17" l="Y" r="Z" v="-10" l="Y" r="a" v="-134" l="Y" r="c" v="-159" l="Y" r="d" v="-131" l="Y" r="e" v="-147" l="Y" r="f" v="-62" l="Y" r="g" v="-142" l="Y" r="i" v="-32" l="Y" r="j" v="-49" l="Y" r="m" v="-94" l="Y" r="n" v="-94" l="Y" r="o" v="-153" l="Y" r="p" v="-94" l="Y" r="q" v="-131" l="Y" r="r" v="-94" l="Y" r="s" v="-115" l="Y" r="t" v="-44" l="Y" r="u" v="-94" l="Y" r="v" v="-69" l="Y" r="w" v="-62" l="Y" r="x" v="-70" l="Y" r="y" v="-65" l="Y" r="z" v="-100" l="Y" r=";" v="-138" l="Y" r=":" v="-154" l="Z" r="A" v="-11" l="Z" r="C" v="-25" l="Z" r="G" v="-24" l="Z" r="O" v="-24" l="Z" r="Q" v="-24" l="Z" r="W" v="-7" l="Z" r="Y" v="-7" l="Z" r="a" v="-10" l="Z" r="c" v="-12" l="Z" r="d" v="-18" l="Z" r="e" v="-31" l="Z" r="o" v="-29" l="Z" r="q" v="-18" l="Z" r="v" v="-45" l="Z" r="w" v="-38" l="Z" r="y" v="-37" l="a" r="f" v="-12" l="a" r="t" v="-19" l="a" r="v" v="-34" l="a" r="w" v="-14" l="a" r="x" v="-19" l="a" r="y" v="-38" l="b" r="f" v="-17" l="b" r="s" v="-10" l="b" r="t" v="-9" l="b" r="v" v="-10" l="b" r="w" v="-10" l="b" r="x" v="-41" l="b" r="y" v="-10" l="b" r="z" v="-28" l="c" r="a" v="-17" l="c" r="o" v="-17" l="e" r="f" v="-18" l="e" r="t" v="-11" l="e" r="v" v="-10" l="e" r="w" v="-10" l="e" r="x" v="-31" l="e" r="y" v="-13" l="e" r="z" v="-20" l="f" r="a" v="-40" l="f" r="c" v="-45" l="f" r="d" v="-53" l="f" r="e" v="-51" l="f" r="f" v="-20" l="f" r="g" v="-60" l="f" r="o" v="-43" l="f" r="q" v="-53" l="f" r="s" v="-27" l="f" r="v" v="13" l="f" r="w" v="6" l="f" r="y" v="10" l="f" r="z" v="-20" l="g" r="a" v="-38" l="g" r="c" v="-12" l="g" r="d" v="-19" l="g" r="e" v="-17" l="g" r="g" v="19" l="g" r="o" v="-14" l="g" r="q" v="-19" l="g" r="t" v="-31" l="h" r="f" v="-12" l="h" r="t" v="-19" l="h" r="v" v="-34" l="h" r="w" v="-14" l="h" r="x" v="-19" l="h" r="y" v="-38" l="k" r="a" v="-35" l="k" r="c" v="-48" l="k" r="d" v="-56" l="k" r="e" v="-66" l="k" r="o" v="-69" l="k" r="q" v="-56" l="k" r="s" v="-19" l="k" r="t" v="-10" l="k" r="u" v="-26" l="m" r="f" v="-12" l="m" r="t" v="-19" l="m" r="v" v="-34" l="m" r="w" v="-14" l="m" r="x" v="-19" l="m" r="y" v="-38" l="n" r="f" v="-12" l="n" r="t" v="-19" l="n" r="v" v="-34" l="n" r="w" v="-14" l="n" r="x" v="-19" l="n" r="y" v="-38" l="o" r="v" v="-9" l="o" r="w" v="-8" l="o" r="x" v="-40" l="o" r="y" v="-11" l="o" r="z" v="-27" l="p" r="f" v="-17" l="p" r="s" v="-10" l="p" r="t" v="-9" l="p" r="v" v="-10" l="p" r="w" v="-10" l="p" r="x" v="-41" l="p" r="y" v="-10" l="p" r="z" v="-28" l="q" r="g" v="10" l="r" r="a" v="-42" l="r" r="c" v="-30" l="r" r="d" v="-28" l="r" r="e" v="-27" l="r" r="g" v="-28" l="r" r="o" v="-33" l="r" r="q" v="-28" l="r" r="s" v="-35" l="r" r="v" v="19" l="r" r="w" v="11" l="r" r="y" v="10" l="s" r="f" v="-19" l="s" r="t" v="-23" l="s" r="v" v="-31" l="s" r="w" v="-10" l="s" r="x" v="-22" l="s" r="y" v="-37" l="s" r="z" v="-18" l="t" r="a" v="-25" l="t" r="c" v="-25" l="t" r="d" v="-23" l="t" r="e" v="-22" l="t" r="o" v="-20" l="t" r="q" v="-23" l="t" r="t" v="-29" l="v" r="a" v="-30" l="v" r="c" v="-25" l="v" r="d" v="-20" l="v" r="e" v="-20" l="v" r="f" v="11" l="v" r="g" v="-28" l="v" r="o" v="-19" l="v" r="q" v="-20" l="v" r="s" v="-9" l="v" r="t" v="10" l="v" r="v" v="12" l="v" r="w" v="12" l="v" r="y" v="12" l="v" r="z" v="-26" l="w" r="a" v="-23" l="w" r="c" v="-20" l="w" r="d" v="-18" l="w" r="e" v="-18" l="w" r="f" v="6" l="w" r="g" v="-18" l="w" r="o" v="-19" l="w" r="q" v="-18" l="w" r="s" v="-18" l="w" r="t" v="4" l="w" r="v" v="12" l="w" r="w" v="8" l="w" r="y" v="12" l="w" r="z" v="-17" l="x" r="a" v="-37" l="x" r="c" v="-46" l="x" r="d" v="-44" l="x" r="e" v="-54" l="x" r="o" v="-55" l="x" r="q" v="-44" l="x" r="s" v="-12" l="x" r="t" v="6" l="x" r="u" v="-20" l="y" r="a" v="-31" l="y" r="c" v="-26" l="y" r="d" v="-24" l="y" r="e" v="-25" l="y" r="f" v="10" l="y" r="g" v="-26" l="y" r="o" v="-24" l="y" r="q" v="-24" l="y" r="s" v="-19" l="y" r="t" v="10" l="y" r="v" v="12" l="y" r="w" v="8" l="y" r="y" v="10" l="y" r="z" v="-17" l="z" r="a" v="-34" l="z" r="c" v="-45" l="z" r="d" v="-46" l="z" r="e" v="-46" l="z" r="f" v="-10" l="z" r="g" v="-17" l="z" r="o" v="-45" l="z" r="q" v="-46" l="z" r="s" v="-22" l="z" r="u" v="-10" l="z" r="v" v="-18" l="z" r="w" v="-22" l="z" r="y" v="-18"  ## Scoring This is , so the shortest answer (in bytes) wins. ### Meta I know this challenge is going to need a lot of work before it's ready for main. Please hold criticisms for now. Helpful ideas and thoughts are welcome. • I'm not sure that the problem is well defined. There's a reason it's called font hinting: the rendering application is free to take it into account or not, or even to apply more complex logic. E.g. some fonts have multiple sets of font hints for different contexts. There are other complex issues. A font can have Latin and Cyrillic letters and define hints for kerning between pairs of Latin and pairs of Cyrillic but not between Latin and Cyrillic; however, some letters may have identical glyphs, so a judgement on whether the kerning is "correct" might be ambiguous. Then there's antialiasing. – Peter Taylor May 24 '17 at 6:15 • @PeterTaylor Good notes. I will likely restrict the character set. I just wanted to start getting ideas down in the sandbox. – Poke May 24 '17 at 6:51 • Very ambiguous. – dkudriavtsev May 25 '17 at 17:48 • @Mendeleev It's not done yet. I'm aware it's ambiguous. – Poke May 26 '17 at 16:10 • Looking at developer.apple.com/fonts/TrueType-Reference-Manual/RM06/… I can see a number of issues to address. 16- vs 32-bit entries? Should multiple tables be combined or printed separately? All tables or only tables with certain coverage values? Which of the four defined formats need to be supported? Do you have a test case which covers glyph index differing from codepoint? – Peter Taylor Sep 16 '17 at 17:28 • @PeterTaylor I have a proof of concept that I wrote (it's the reason I have taken so long to update this) and I'm planning to address all of your questions. Thanks for doing a bit of research to help me out, though :] – Poke Sep 16 '17 at 18:57 • Downvoter, why? – Poke Oct 4 '17 at 21:03 # Shift-left golfer Sometimes when doing code-golf, a person needs to understand which format is shorter: • 2147483648 • 0x80000000 • 1<<31 The task: 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? – HyperNeutrino 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 Six Flags over HTTP Let's say you need to transmit six boolean flags in a URL string. Obviously you could do it with six ones or zeroes, but you want better compression. With a little math you can pack them into two characters using 0-7 octal. How about mapping all six to a single ASCII character? Here we have a problem: you are not allowed to use , / ? : @ & = +$ # or space. Now the range of printable ASCII no longer has 64 valid characters in a row.

In Javascript (or another language that can run from a web page, if any), what is the shortest code for a pair of functions to encode and decode this data, between an array of six booleans and a single character?

• -1 language restriction, most languages have HTTP libraries so I think any language should be allowed – ASCII-only Sep 24 '17 at 13:11
• This challenge could be improved by rephrasing it to: "Write a bijective function between an array of six booleans and a single printable character excluding the characters ,/?:@&=+\$# ". Mentioning that the encoder and decoder should be separate programs/functions would be helpful. Also, may the encoder and decoder share code? – fireflame241 Sep 24 '17 at 22:08

# 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

# Count letter frequency

Inspired by question Tweetable hash function challenge, you should take the English dictionary used there and produce a program or function that outputs the the absolute and relative frequency of each character. It is CASE SENSITIVE and the APOSTROPHE is also accountable as a real letter.

Example of a valid output format (but with stupid guessing values):

A      5566    20%
...
Z        60     0.2%
a     27000    30%
...
z       120     0.01%
'       450     3.5%


It is , but no answer will be accepted. Wanna know shortest script for each language.

• -1 (01) Don't rely on another challenge to define yours; include all the information we need in your write-up. (02) Make an effort to come up with some actual test cases - do you honestly expect us to verify our solutions against "stupid guessing values"? – Shaggy Sep 30 '17 at 0:55

# 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? – HyperNeutrino 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? – HyperNeutrino 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 – HyperNeutrino 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

# Is it a perfect loop? test-batterydecision-problem

Your task is to take a GIF or an animated image in any reasonable format as input (including taking the file name of a GIF in the current directory), and output whether it is a "perfect loop" - that is, the frames transition seamlessly from the end to the start, and a human cannot notice where it starts and ends at first glance. Return or print a truthy value if it is a perfect loop, otherwise print or return a falsy value.

## Scoring

Winners will be determined from the percentage of test cases they get correct. In the event of a tie, highest votes wins. You can view test cases at https://ghostbin.com/paste/m3yaw. Show your score against the test cases when you post.

## Input

If you are not taking input in a GIF, please provide a program that will convert a GIF to your desired format.

Images corresponding to a truthy value have been taken from /r/perfectloops and for falsy test cases, /r/almostperfectloops and /r/gifs.

## Restrictions

• Hard coding is not allowed (violates standard loophole 1 and 2).
• You must provide consistent results for the same GIF (no randomness)
• Remember, this is not , so byte count is not needed in your solution. Just post the language name and add the percentage correct when I comment.
• I'm not sure it's as simple as comparing the first to the last frame, if it is we'd have duplicate frames. is this challenge allowing HTTP requests? – tuskiomi Oct 17 '17 at 21:15
• If hashing the inputs is not allowed, then you should clearly define what constitutes a “perfect loop”. It's not good to extrapolate from a handful of test cases where the pass/fail cases are very similar. – japh Oct 18 '17 at 14:31