# 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]

# Compute the mincut of a graph code-golf

Given a graph, compute a division of the graph such that the edges stranded between the cut.

Red line: a cut

Green line: a mincut

## Input

The first line will contain the number of nodes. The rest of the lines will contain pairs of positive integer IDs separated by spaces showing connectedness between the nodes with those IDs. Here's an example; for a graph where 1 is connected to 2 and 2 is connected to 3:

3
1 2
2 3

• You may assume that the nodes are numbered consecutively from one to the number of nodes.
• However, you may not assume that the list of pairs of nodes is in any specific order.

## Output

Simply output a comma-separated list of the IDs of the nodes of one of subgraphs created by the cut.

• You cannot implement brute-force search. Other than that, feel free to use Karger's Algorithm* or another algorithm. Remember that Karger's algorithm is likely the easiest to implement.
• Notice: you must run Karger's algorithm at least this many times to ensure a low chance of failure and a low chance of failure

## *Karger's algorithm

For your convenience, I've included a simple description of Karger's algorithm.

1. find two adjacent nodes and merge them into one node (so that all nodes that where connected to the original two nodes are connected to the new node), concatenating the labels
2. repeat step one until there are only two nodes
3. the result is any label of one of the nodes
4. repeat steps 1-3 at least this many times to ensure a low probability of failure, and choose the result that occurs the most often
• 1. Wouldn't it be better to take the graph as an adjacency matrix or list? 2. Your description of the minimum cut is somewhat confusing. 3. Karger's algorithm is probabilistic, which isn't allowed by our defaults (I don't think). Allowing probabilistic algorithms opens up a whole can of worms (for instance I could write a program that just returns a random cut) -- you should probably make it so that the algorithm must return the minimum cut two-thirds of the time or something similar if you want to allow them. – a spaghetto Jul 5 '16 at 0:07
• @quartata 1. it's an adjacency list 2. yeah I need help with that 3. I made sure you had to repeat it insert some math equation here amount of times – noɥʇʎԀʎzɐɹƆ Jul 5 '16 at 0:13
• Sorry I misunderstood the input. – a spaghetto Jul 5 '16 at 0:14
• Generally adjacency lists are done like [node1, connected_node1, connected_node2, ...] and not in pairs like you have it; this is more flexible and you don't have to specify the number of nodes (it is just the length of the input list) – a spaghetto Jul 5 '16 at 0:35
• "You cannot implement brute-force search" is too vague. What about a basically brute force search that shortcuts some obviously wrong possibilities? I think what you want is a running time bound. – xnor Jul 5 '16 at 1:55
• 1. The I/O description seems to assume that all answers will be programs taking input on stdin and writing output to stdout, but our defaults are more flexible. In particular, by default we allow answers to be functions which take arrays and return arrays. Comma-separating is also IMO unnecessarily constrained, especially as the input isn't comma-separated. – Peter Taylor Jul 5 '16 at 7:51
• 2. "Feel free to use Karger's algorithm or another algorithm". There's an implicit licence here to use another non-deterministic algorithm, but although you give an explicit iteration count for Karger's algorithm you don't for e.g. randomised Kruskal's algorithm, which it's based on. 3. Besides which, in general I don't think that questions should tell people which algorithm to use. Specify the task and constraints (e.g. "Randomised algorithms are allowed, but must find the correct answer with probability at least foo. All answers must be polynomial-time"). – Peter Taylor Jul 5 '16 at 7:54
• 4. But if you're going to include an algorithm description, be careful to get it right. Karger's algorithm is randomised, but in the description given there's no mention of where the random selection occurs or of what uniformity constraints are required to get the desired behaviour. – Peter Taylor Jul 5 '16 at 7:55
• Food for thought: outputting the value of the min cut instead might lend to more approaches. Also, any rules on min cut/max flow/possibly other optimisation builtins? – Sp3000 Jul 5 '16 at 10:34
• I'm going to add a story to this soon. – noɥʇʎԀʎzɐɹƆ Jul 5 '16 at 13:55

# Generate a random Vietnamese syllable

tags:

The Vietnamese syllable space is interesting, because it is huge.

TODO: Describe the space and why it is interesting.

Here's how such syllables are made:

The onset matches the regex ^([bcdđghklmnprstvx]|qu|[cgkpt]h|ng|tr)$The vowel is one of the following massive list: a à a' ã á a. â â â' â~ â´ â. a. ă ă' ă~ ă´ ă. e è e' e~ é e. ê ê ê' ê~ ê´ ê. i ì i' ĩ í i. ia iê o ò o' õ ó o. oa oă oe ô ô ô' ô~ ô´ ô. o' ò' o" õ' ó' o'. u ù u' ũ ú u. ua uâ uê ui uô uo' uy u' ù' u" ũ' ú' u'. u'a u'o' y y y' y~ ý y. ya yê The coda matches the regex ^([iouycptmn]|ch|ng|nh)$


(thanks Peter Taylor!)

The onset, vowel and coda are concatenated to make the result syllable.

## Objective

The objective is to generate random Vietnamese syllables. Your program has to take no input and as output include only the syllable, with an optional trailing new line.

## Clarifications

• Each syllable must be generated with a non zero probability.

I think it's unclear. Contributions are so much welcome.

• 1. I'm not sure what you mean by can be with. 2. You don't mention randomness anywhere excwpt the clarification. 3. Object should probably be Objective. – Dennis Jul 3 '16 at 18:44
• 1. c can also be with h means that h can follow c as the 2nd stage letter in the syllable. 2. Where should I also mention it? 3. Ah k :) – user48538 Jul 3 '16 at 18:46
• If I'm reading this correcting then it can be vastly simplified by saying that the onset matches the regex ^([bcdđghklmnprstvx]|qu|[cgkpt]h|ng|tr)$, the vowel is one of a massive set of options (I don't see any benefit to splitting that into "stage 2" and "stage 3"), and the coda matches the regex ^([iouycptmn]|ch|ng|nh)$ – Peter Taylor Jul 4 '16 at 16:36

# Let's play some Briscola

Briscola is an Italian game, played with a deck of 40 cards, divided in 4 suits - coins (denari - D), swords (spade - S), cups (coppe - C) and clubs (bastoni - B).

The values on the cards range numerically from one through seven, plus 3 special cards - knave (11), knight (12) and king (13).

## Gameplay:

After the deck is shuffled, each player is dealt three cards. The next card is placed face up on the playing surface, and the remaining deck is placed face down. This card is the Briscola, and represents the trump suit for the game.

First player starts by playing one card face up on the playing surface. Each player subsequently plays a card in turn, until all players have played one card.

The winner of that hand is determined as follows: If any briscola (trump) has been played, the player who played the highest valued trump wins, else the player who played the highest card of the lead suit (suit of the first card played) wins.

## Ranking

Briscola has a special type of ranking:

1   ace
3   three
13  king
12  knight
11  knave
7
6
5
4
2


## Rules:

Standard loopholes apply.

### Input:

As an input, you must accept 5 values (cards), in a reasonable format, for example:

briscola (trump card), 1. card, 2. card, 3. card, 4.card


### Output:

You must output the winning card

### Example input and output:

4S 7D 12B 13B 2S -> 2S
5D 1D 5D 12S 3C -> 1D
3B 2C 4S 5S 7D -> 2C
12D 3S 11B 1B 7S -> 3S

• As mentioned in chat, I think this is probably a duplicate of this challenge. Just adding so other people don't have to go looking. – FryAmTheEggman Jul 6 '16 at 21:15

# nth number that multiplies k equals its reverse

Tags: ,

It's quite simple, given n and k, output the nth number such that, if the number is multiplied by k and its digits reversed, it equals the original number. Both input and output are positive numbers.

The challenge originally is from Mego, posted on my broken challenge. Firstly, I used 4 instead of k, but based on my tests, only 1 and 4 values gives output, so I decided to put 4 instead of k, finally I put k back. But the challenge would be ruin with that putting "9"*(n-1) between 2178, so no loopholes will be permitted.

I just posted here for further discussions, suggestions and improvements.

• Those numbers are positive right? – Fatalize Jul 6 '16 at 7:52
• Please add some examples of expected outputs. – Fatalize Jul 6 '16 at 7:53
• Also you might want to prevent people from hardcoding 2178 in any fashion in their code so that they have to compute the numbers, because it seems they all are of the form 21X...X78 where X...X is a series of nines (except for the first one, which is 0). – Fatalize Jul 6 '16 at 7:56
• According to the community advises, I'm not allowed to prevent people use methods those work perfectly. – Ehsaan Jul 6 '16 at 8:23
• Let's wait to see what others think. I personally don't think it's very interesting if people are allowed to hardcode the "format" of those numbers. – Fatalize Jul 6 '16 at 8:26
• Me neither, I think the challenge isn't interesting at all. – Ehsaan Jul 6 '16 at 8:43
• I think there's no good way to prevent hardcoding. Maybe making "4" were an input parameter as well would make solutions actually search for an answer? – xnor Jul 6 '16 at 9:01
• @xnor You mean make 4 as k input? – Ehsaan Jul 6 '16 at 9:33
• @Ehsaan Yes, exactly. – xnor Jul 7 '16 at 9:09
• 9 works too: 1089 * 9 = 9801. – Neil Jul 10 '16 at 17:36

Write a program that can determine the median value of a read-only (static, const, immutable) sequence of unsorted numbers (array, list, stream) but minimises storage, without completely sacrificing speed.

The basic bracket is that if we copied all the values into a sorted list and then picked the middle one (or average of the middle pair), it would require storage of the whole sequence, so the storage would be 'n', and the performance would be O(n log n).

The score is the total cost of finding the median of 1 bn values, divided by 1 bn, at a cost of 8 per value stored, 1 per comparison or numerical operation and 1 per read, for the worst case. Thus if our insertion sort costs exactly n*log2(n), the for 1 bn values the total score is 1 for the read, 29.8 for the sort + 8 for the storage, for a total of 37.8.

If instead we skimmed the whole range to get the average (costing 1 for the read and 1 for the summation), we could then only store some portion of the range to sort; but then we would need a second pass to be sure that there were an equal number of values above and below this median (at the cost of another 2).

Lowest score wins, low-level languages (C/C++/D) only so that we can count the actual operations.

• 1. It's not clear to me what counts as a "value stored" or a "read", and I think there are probably gray areas with "comparison or numerical operation" too. (E.g. in C is if (foo) a comparison?) 2. "The score is the total cost ... for the worst case." For any non-trivial algorithm, the full calculation of this score risks being longer than the code. There's a reason that complexity theorists deal with Landau notation rather than exact operation counts. – Peter Taylor Jul 7 '16 at 13:39

# Reinventing the Modularization Wheel

In a language of your choice, implement a function or language construct that imports another file of the same language and executes it, making exported values from that file available to the calling file. If one already exists, you may not use it in your implementation.

For example, in Node, you would have to implement require() without using require(), even indirectly. In C, you would implement a function or construct equivalent to #include without using #include in the implementation. In Python, you would implement import. In client-side JavaScript, I suppose the closest equivalent would be <script src="..."></script>. So JavaScript implementations would be restricted to AJAX calls only, since <script> tags would not be allowed in the implementation.

This is not to say that you aren't allowed to use the built-in import at all, but only use them in the implementation. The intention here is to reinvent the wheel.

## Requirements

• Do not include the built-in modularization in any way in your import implementation.
• Standard libraries only.
• Byte-count includes the implementation itself, and any special changes that need to exist on the file being imported, if any.
• The function or construct accepts a relative file path. As long as this is satisfied, you may extend the functionality of your modularization to have global imports, or even remote imports (like using a URL as input).
• The imported file must have a construct for denoting values that must be exported. Only these values should be directly accessible from the calling file.
• Using the built-in export function or construct of your language is acceptable, and if it is a built-in, it does not need to be included in your byte-count.
• If your language does not have modularization, then implementing a mechanic for exporting should be included in your byte-count.
• Document the usage of your function or construct.

### This is code-golf and the shortest answer in bytes wins!

• Perhaps just restrict this to languages which support modularization to avoid loopholes – Downgoat Jul 7 '16 at 18:45
• @Downgoat if people wanted to use a built-in for reading a plaintext file, and then use an eval()-like built-in to execute it in a way that exposes only denoted values (however you define that), I think it would be acceptable. What sort of loopholes do you foresee? – Patrick Roberts Jul 7 '16 at 18:49

# Print a Pilcrow Scarecrow

Print the following ascii scarecrow using the pilcrow character ¶

    ¶¶¶
¶¶¶¶¶
¶¶¶
¶¶¶  ¶
¶¶¶¶¶¶¶¶¶¶
¶¶¶
¶¶¶
¶ ¶ ¶
¶¶ ¶ ¶¶
¶
¶
¶¶¶¶¶¶¶¶¶¶¶

• Padding must be with   (space) and built with ¶
• Print to stdout
• This is

# It's time to unify!

## Introduction

Wouldn't it be awesome if they whole world would be united and there would be no conflicts and disputes? Now while you can't unify nations, you certainly can unify expressions to resolve their unknown relation and conflicts.
Your mission is simple: Unify the world (of expressions)!
And of course, because you're lazy you want to do this with the least effort (read: code-length) possible.

## Specification

### Input

Your input will be a unification problem. You can format it however you want and need, as long as you don't encode additional information to what is given in the standard / example format. Encoding the number of arguments per function into the input is allowed but not mandatory, you can also just derive this from the input.

Example format:
Your first input will be list of function symbols, which is represented as a list of pairs of strings and non-negative integers.
Your second input will be a list of equalities (you may represent each as a string), which represent the unification problem. They will be represented as a list of strings as well. Anything which is not a parenthesis or an equality sign can be considered a variable. If the number of arguments is 0, parenthesis are omitted.

Example input: [("f",1),("g",2),("h",3),("a",0)], [x=f((g(a,y)),y=h(g(f(a),z),f(z),a)]

### Output

The output is either some falsy value or something representing a list of equalities. It is allowed to use the empty list to indicate a falsy value.

### What to do?

You need to unify the inputs you got. In the end there must only be variables on the left side of the equality-signs if the you didn't encounter an error. If you did you need to report it (-> false or empty list).

To do the unification, you can - but don't have to - use Martelli and Montanari's algorithm, which goes as follows:

E is always the (complete) set of equalities except the current one
x,y,z are variables, f,g,h are functions, t1,t2, ...,tn,s1,...,sn are arbitrary terms (compositions of functions and variables)
{x=x} E => E, e.g. if you encounter two equivalent variables, discard
{f(t1,...,tn)=f(s1,...,sn)} E => {t1=s1,t2=s2,...,tn=sn} E, e.g. if you encounter the same function on both sides, unify the arguments along with your rest
{f(t1,...,tn}=g(s1,...,sn)} E => Error, if the symbols are different, you can't succeed
{x=f(t1,...,tn)} E => {x=f(t1,...,tn)} E[x -> f(t1,...,tn)], e.g. if you see a variable equals a term, replace the variable with this term in all other expressions
{x=f(t1,...,tn)} E => Error, e.g. if any of the t1,..,tn contain x at some point
{f(t1,...,tn)=x} E => {x=f(t1,...,tn)} E, e.g. if you see a variable "naked" on the right side, swap the sides


Two step-by-step examples are provided below additionally to the test cases.

### Corner Cases

You can get an empty list of function symbols, this means you have exclusively variables in the second input.
The input list of equalities will never be empty, your code does not need to handle this case.

### Who wins?

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

## Test-cases

All these test cases use the functions [("a",0),("b",0),("f",1),("g",1),("h",2)]

[x=b] -> [x=b]
[a=x] -> [x=a]
[a=b] -> []
[y=f(x)] -> [y=f(x)]
[x=f(x)] -> []
[f(x)=f(y)] -> [x=y]
[f(x)=g(y)] -> []
[h(x,y)=h(a,b)] -> [x=a,y=b]
[x=f(z),y=f(a),x=y] -> [x=f(a),y=f(a),z=a]
[h(x,f(y))=z,z=h(f(y),v)] -> [x=f(y),v=f(y),z=h(f(y),f(y))]


### Step-By-Step Example

Example 1: Test Case 9
[x=f(z),y=f(a),x=y] => (replace x in third equation with first x)
[x=f(z),y=f(a),f(z)=y] => (replace y in third equation)
[x=f(z),y=f(a),f(z)=f(a)] => (remove f's in third equation)
[x=f(z),y=f(a),z=a] => (replace the z in the first expression)
[x=f(a),y=f(a),z=a]

Example 2:
[f(g(a,x),g(y,b)=f(x,g(v,w)),f(x,g(v,w))=f(g(x,a),g(v,b))] => (remove f in second equation)
[f(g(a,x),g(y,b)=f(x,g(v,w)),x=g(x,a),g(v,w)=g(v,b))] => (function symbol missmatch in equation 2)
[]


# create a golfed down regexp that matches all substrings

inspired by Determine the "Luck" of a string where I found a way to golf almost 30 bytes at once
(with a falling trick for that challenge, but I still like the idea).

The word "lucky" contains 15 different substrings:

• lucky
• luck, ucky
• luc, uck, cky
• lu, uc, ck, ky
• l, u, c, k, y

Challenge
Create a program or function that, for a given string s, creates the shortest possible regexp using basic PCRE syntax that matches and returns all substrings of s and nothing else.

• code needs not to be case sensible
• basic syntax means: alternatives, quantifiers, grouping and custom character classes (e.g. [abc])
• other features (assertions, backreferences, recursion etc.) may be used, but are not required to qualify
• the result may include delimiters and modifiers

The result for lucky would be l?ucky?|l?uc?|c?ky?|l|c|y.

• is the description sufficient?
• the challenge not too easy, not too hard?
• any other hints you might have?
• I will add test cases that expose possible bugs (like silly and digdug)
• not sure yet if I will go for shortest code yet

# Write a Gopher Interpreter

This code golf challenge will task you with writing an interpreter for an esolang I created a while back called Gopher, Details on the language can be found Here

# Pass Conditions

This challenge requires you to create an Interpreter (Or you could go a step ahead and create a Compile/Transpiler) however for the code to pass as correct it must meet the following criteria

• Take in a single input being the Gopher Code
• Output the result of the Interpreted code

• Invalid code does not need to be handled, however you may do so if you wish

• As this is code-golf the smallest byte size wins

# Example Input and Output

Input:

&++<'×<&÷+<^-<<×-<#!+<$@-<&@<×-<@++<@<.!<=  Output: Hello World  • Thanks for using the Sandbox! Anyway, you should add the relevant information on Gopher to the body of this post, as if your github account/repo dies or is changed people still need to be able to answer this question. – FryAmTheEggman Jul 11 '16 at 17:15 Having had a look, it seems there isn't a challenge for "Given any date, output the day of the week". Is that a challenge worth having? Something like "Given an input date, in the form dd/mm/yyyy, output the day of the week" Shortest code wins What do we think? perhaps this already exists and I didn't find it. • Duplicate – AdmBorkBork Jul 11 '16 at 14:04 • Glad I checked! – Matt Jul 11 '16 at 14:05 # Golf your way from (inc|dec)rements to the basic math operations Write five different functions or programs that do addition, subtraction, multiplication, division and modulo with integers by only using increments, decrements, loops/recursion and comparisons. • Assume division & modulo will never receive 0 or negative integers as the divisor/modulus. • Modulo's result has the sign of its dividend. • Division truncates its quotient, e.g divide(11, 4) returns 2 and divide(-5, 3) returns -1. • Programs must print the result to STDOUT. Functions must return the result. • Your five functions/programs may invoke each other. • All functions/programs must support 32-bit signed integers, i.e everything between -231 and 231-1 (inclusive). Overflow is allowed, i.e it's OK if add(2147483647, 1) returns -2147483648. • Explicitly adding/subtracting 1 to/from numbers is allowed, in case you use a programming language that doesn't have built-ins for incrementing and decrementing. • Shortest program wins as long as it doesn't exploit standard loopholes! I seriously have no idea how to make test cases for this. • Why not one function that returns all of those? You should also specify what you mean by divisions and modulo as they differ slightly from language to language. (E.g. what is -2 mod 5? and what is -1/2?) And only doing increments/decrements, loops/recursion and compraisions is also quite vague. – flawr Jul 10 '16 at 16:37 • I don't think test cases would really be necessary since it's just basic arithmetic. You can easily tell if your output is correct or not. Also, I'm assuming that division will truncate the quotient since there isn't really any way to do decimals in this fashion, but that should probably be specified. – Business Cat Jul 11 '16 at 14:18 • I already did this because I was bored... – univalence Nov 19 '16 at 12:52 ## ASCII to Unicode equation beautifier You may well be used to typing equations in ASCII, but with the advent of Unicode we can spruce them up a bit. We can fix • Powers (numeric superscripts only) • Numeric subscripts • Mathematical signs (-, *, / ^ → -, ×, ÷, ↑) Examples: x^3 - 1 = (x - 1)(x^2 + x + 1) → x³ − 1 = (x − 1)(x² + x + 1) g_0 = 3^^3^^3 -= 3^(3^3) → g₀ = 3↑↑3↑↑3 = 3↑(3³) 800*600 → 800×600 1/x → 1÷x  You may assume that all digits directly after a ^ or _ are meant to be super/subscripts (and the ^ or _ to be removed) and that all the mathematical signs are to be replaced wherever they appear. This is , so the shortest solution wins. • This seems to be two questions crammed into one. The first one is the superscript and subscript transformation, which is mildly interesting; and the second one is the straight substitution of various characters for others, which is completely boring apart from the ambiguity it introduces in the interpretation of ^. I suggest ditching the substitution of minus, times, and divide symbols and giving explicit lists (with copyable characters and Unicode code points in decimal and hex) of the superscript, subscript, and up-arrow characters. – Peter Taylor Jul 14 '16 at 6:39 # Autotune a chord Auto-Tune is a pitch correction program which alters the pitch without changing the length. It can be used to fix off-pitch chords in music, which is good because I have an out of tune piano. The goal of this challenge is given some input waveform which contains a single chord played on my piano, tune each note to the nearest equally tempered note found on a standard piano (see Input for more details). # Input The input is something which looks like a time-domain audio sample input containing a single chord being played. All data is sampled at 192kHz, with 16-bit PCM (little endian integer), mono channel. The input may come from any source desired (file io, stdio, function parameter, etc.). # Output The output of your code should be something which looks like a time-domain audio sample containing the tuned chord. It does not need to have the same sample rate or datapoint format as the input, but must be the same length in real time as the original sample (or as close as possible). The output may be to any source desired (file io, stdio, function parameter, etc.). # Examples See this github repo for various inputs and outputs. The provided examples have inputs/outputs in an uncompressed wav file. Feel free to re-encode/gut the data for your inputs. # Scoring This is code golf; shortest code wins. Standard loopholes apply. You may use any libraries/builtins so long as they were not designed specifically for performing pitch correction. Main concern: This challenge seems potentially too difficult, so one alternative I've been considering is changing the piano samples into sine waves at the fundamental frequencies (avoids issues with amplitude decay/harmonics). An even simpler challenge might be to give inputs in the frequency domain (list of fundamental frequencies), though I'm not sure that would make for an interesting challenge as it seems almost too easy at that point. • It seems very difficult to determine what outputs are considered correct. – feersum Jul 14 '16 at 7:44 • yeah, that thought had crossed my mind as well. I've considered measures based on the delta of the FFT of user output/expected output, but I'm not sure this is necessarily a good measure of "in tune". – helloworld922 Jul 14 '16 at 7:47 • I suspect that the biggest technical challenge would be phase. The harmonics of each string in isolation should be in phase, because they all derive from a single hammer strike, but the keys of the chord are probably not all struck at exactly the same time, and there will be resonant driving interactions between them which will complicate the signal. I suggest that you explicitly state that people can ignore this issue. – Peter Taylor Jul 14 '16 at 13:39 This will be a challenge. Additional tags are , and . # How fast is your Stack Exchange community? tl;dr Your task is to find how fast a Stack Exchange community reacts. "How fast" is here the average of the time elapsed until the first answer or the closing of the question. Input • the Stack Exchange site's name, e.g. stackoverflow, codegolf, codereview etc. • optionally the Stack Exchange API URL: https://api.stackexchange.com/2.2/ Requirements • Calculate the average time it takes until the first answer or closing of the question. • Take the 1000 latest questions into account, e.q. ten API requests with 100 items each. Output • Output the average time in minutes and seconds, like 01:23 or 1:23. • Run your program at least against stackoverflow, codegolf and code review and show the results. • Feel free to add results for your other favorite communities as well. Boilerplate • You can write a program or a function. If it is an anonymous function, please include an example of how to invoke it. • This is so shortest answer in bytes wins. • Standard loopholes are disallowed. • Leading/trailing whitespaces/newlines are fine. • How do you count unanswered and unclosed questions? Also, I don't know about the API, but there might be problems with deleted answers. I think you should probably write a reference implementation before posting this. – FryAmTheEggman Jul 14 '16 at 13:10 • @FryAmTheEggman Thanks a lot – all good points. Didn't think that there might be questions that are unclosed and unanswered. Will check the API whether deleted even will be send. Good point with the reference implementation – maybe in JavaScript that it can be run as a stack snippet. What do you think in general about the challenge idea? Boring? Interesting? Too complicated? – insertusernamehere Jul 14 '16 at 13:15 • It's about doing basically one task, so I don't think it is complicated. I think the results are probably more interesting than the challenge (there are only so many ways to average something and to parse html), but it makes sense and isn't trivial, so I wouldn't say it's boring. Seems fine overall. Also note internet, date and, I suppose, math. – FryAmTheEggman Jul 14 '16 at 13:24 • @FryAmTheEggman Thanks again for your feedback and the tag suggestions. I also think that the results are the interesting part. I wanted to try a popularity contest in the first place because of that. But I couldn't come up with the necessary criteria. :) – insertusernamehere Jul 14 '16 at 13:30 # Convert a BMP image to grayscale The images manipulation is a great way to exercise and increase your skills. In my opinion it's also very interesting. # What you must do? The objective of exercise is much easy: convert an image bmp colorful in an image grey. You can use every language, the question most appreciated will be that don't use library. Image stock: http://www.mediafire.com/convkey/c491/p7aya9cxafvfc91zg.jpg Image converted: http://www.mediafire.com/convkey/3903/rcigd79pkwd12qczg.jpg?size_id=3 • What is the winning criterion? It is code-golf, popularity-contest, other criterion? – TuxCrafting Jul 15 '16 at 10:30 • Also, the You can use any language is unnecessary, it's implied here. And you can use ![](<image url>) to show the images. – TuxCrafting Jul 15 '16 at 10:33 • This is very underspecified at present. 1. What weights should be used in the conversion from RGB to greyscale? 2. What bit depths should be supported? 3. Is it required to support all of BMP's features (e.g. ICC colour profiles, CMYK, JPEG, PNG)? If not, what is the minimum feature set which must be supported? – Peter Taylor Jul 15 '16 at 10:53 • @Blind To mention someone, you can use @<username>, and please add the tags to your post ([tag:<tag name>]) – TuxCrafting Jul 15 '16 at 12:43 • @TùxCräftîñg , It's a code-golf. @ Peter Taylor , It's equal, you can use that weight you want. 2.see 1st. 3.just support BMP. – Blind Jul 15 '16 at 16:27 • That doesn't actually answer questions 2 or 3. – Peter Taylor Jul 15 '16 at 19:32 • Just to let you know, you can only @mention one person per comment, and it won't work with a space between the @ and the name. – trichoplax Jul 20 '16 at 16:20 # Do I have an emoji? Given an input string in your language, return truthy/falsey if the input contains an valid Unicode emoji character. ## What is an Emoji? The word emoji comes from the Japanese: 絵 (e ≅ picture) 文 (mo ≅ writing) 字 (ji ≅ character). Emojis are pictorial symbols used to represent feelings, actions, or objects. For this challenge, use the Full Emoji Data list provided by Unicode as a reference to determine which characters are valid Emojis. Sample test cases: "" -> 0 "💩" -> 1 "hello💩" -> 1 "hello" -> 0 "!±≡𩸽" -> 0 Discussion: This seems trivial, but I noticed we didn't have an emoji detection challenge. There might be a concern about the encoding of the input string, but reading the linked meta posts about Strings I feel that this challenge can use whatever String format the language used in the answer supports. The acceptable output for booleans is also up for discussion. Do we have a meta post on what output formats are acceptable for booleans? • One question: What exactly is an emoji? I think it should be specified in the challenge. – user48538 Jul 18 '16 at 16:38 • See meta.ppcg.lol/q/2190, just say truthy/falsey. – LegionMammal978 Jul 18 '16 at 16:39 • @zyabin101 can I use Unicode's emoji list as a list of valid emoji characters for this challenge? – JAL Jul 18 '16 at 16:44 • Up to you. [filler text] – user48538 Jul 18 '16 at 16:51 • I've attempted to clarify what an emoji is, at least for this challenge. Hopefully this will make this question more clear and a better fit for the site. – JAL Jul 19 '16 at 2:39 • A source which gives actual ranges would be more convenient for people writing answers, although unicode.org/Public/emoji/3.0//emoji-data.txt isn't entirely consistent with the other lists. – Peter Taylor Jul 19 '16 at 9:52 ## Trim trailing spaces in less than O(n²) time Since s/\s+$// runs in O(n²) time, Stack Overflow needs to replace it with something faster. Please write a code snippet for them. Your score will be the number of bytes in your submission, multiplied by the time taken to process a string of 1000 non-spaces with 1,000,000 leading and trailing spaces, divided by 1000 times the time taken to process a string of 1-non space with 1,000 leading and trailing spaces. (In other words, if your code runs in O(n) time then this should cancel out.)

• The fancy scoring seems like it might be confusing/hard to implement. Why not just restrict the complexity to be less than O(n²) like you suggest in the title? – FryAmTheEggman Jul 21 '16 at 13:18

## Test Cases

The test cases given below are the output for a program/function using the shortest "wrapping" version of the constants at http://esolangs.org/wiki/Brainfuck_constants.

Input
Output
Brainfuck program's output

72.>105.>33.
-[>+<-------]>-.>+[->-[<]>--]>.>>-[-[-<]>>+<]>.
Hi!

255>10++>65>255<+[-<+]->[-+[->+]-<.+[-<+]->]
->++++++++++++>>+[+[<]>>+<+]>>-<+[-<+]->[-+[->+]-<.+[-<+]->]
AAAAAAAAAAAA

>0>48-->255<[>>86.[-]+[-<+]-<-]
>>-[>+<-----]>----->-<[>>-[>+<---]>+.[-]+[-<+]-<-]
VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV

>,[>,]<[<]>[.>]
>,[>,]<[<]>[.>]
(cat - outputs the input)


## Scoring

Your score is your byte count plus the average length of your program/function's output for each number. For example, if a 30 byte program's output had an average length of 13.5, its score would be 30 + 13.5 = 43.5.

## Sandbox Questions

Is it tagged correctly? Should this be instead of ?

• To prevent hardcoding, add the length of the output to their score – Nathan Merrill Jul 31 '16 at 13:52
• I don't understand "the code you generate must also be as small as possible." The spec requires using the "shortest Brainfuck representation according to esolangs.org/wiki/Brainfuck_constants", so the code generated should be identical for every valid answer, surely? – Peter Taylor Aug 1 '16 at 14:21
• @PeterTaylor Oops! Forgot to remove all references to that URL. I'll fix that now. It's meant to be optional to use it, a previous version of the spec required it. – Copper Aug 1 '16 at 14:37

# Convert hexagonal coordinates to index

Your job is to, given the size of the hexagon and a pair of axial coordinates, return the index as if all the rows were laid out side by side.

Here's an example mapping for size 3:

(q,r), 3

(0,0) (1,0) (2,0)
(-1,1) (0,1) (1,1) (2,1)
(-2,2) (-1,2) (0,2) (1,2) (2,2)
(-2,3) (-1,3) (0,3) (1,3)
(-2,4) (-1,4) (0,4)

maps to

00 01 02
03 04 05 06
07 08 09 10 11
12 13 14 15
16 17 18


Here's the formula I found (could be improved):

i=index
s=size

i = q + sum( ( 2 * s - 0.5 - abs( x - s + 0.5 ) ) for x in 1..r )


Test cases (0-based indexing):

(q, r, s) -> i

(0, 0, 1)  -> 0
(0, 0, 50) -> 0
(0, 3, 3)  -> 14
(-3, 5, 4) -> 28
(5, 2, 12) -> 18
`

Meta notes:

• Should I include links to axial coordinates and centered hexagonal numbers?
• Or, instead, should I explain axial coordinates better?
• Should I include the formula I came up with?
• More test cases, or are those fine?
• More exposition?
• I'm also planning to do a challenge the other way around, is that ok?
• This technically isn't related to Hexagony (though, you can keep the reference if you'd like). I personally wouldn't include the formula, but that's my opinion. The reverse challenge seems like a good one as well. – Nathan Merrill Aug 3 '16 at 15:58

# Rules

• Your program must take no input and print this text.
• You can have trailing newlines, and spaces after lines.
• You must not use a builtin or load the text for an external resource.

# Score

This is , shortest answer in bytes wins.

Did you guess what was the text?

• 10/10 very creative and interesting – Leaky Nun Aug 4 '16 at 11:17
• What is special about the text and means that the answers won't use the exact same techniques as previous kolmogorov-complexity questions? – Peter Taylor Aug 4 '16 at 13:35