Sandbox for Proposed Challenges

Question

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Answer 1

White Water Rafting

code-golfpath-findinggraphsgrid

---

This problem is about finding the best path through a bunch of rocks on a 5-column wide river, without crashing your raft. A river looks like this (* reprsents a rock):

. . . R .
. R . . .
R . . . .
. . R . .
R . . . .
. . . . R

Each row will contain exactly 1 rock, no more, no less. Your raft can start on any space without a rock.

You can't maneuver your raft too much, so as you travel down the river, there are only 3 next places you can go (x is the next space):

. . @ . .
. x x x .

If there is a rock in your way, you can't go there. Your raft can't fit through rocks that are diagonally adjacent to each other. You can't beach your raft either. Finally, you can't go anywhere that would result in you crashing your raft.

@ . . . .
R x . . .   <- Can't go on rock, can't go oob

R . . . .
. R @ . .
. . R X .   <- Can't go through diagonal rocks

. @ . R .
. R x . .   <- Can go through non-adjacent diagonals,
R . . . .      Can't go to dead end.

Because you don't have much space on the raft to write this code, shortest code wins.

Test cases:

Input:

. R . . .
. R . . .
. . . R .
. . . R .
R . . . .

Output:

R x . . .
. R x . .
. x . R .
x . . R .
R x . . .

Input:

R . . . .
R . . . .
R . . . .
R . . . .
R . . . .

Output:

R x . . .
R x . . .
R x . . .
R x . . .
R x . . .

Input:

. R . . .
. R . . .
. R . . .
. R . . .
R . . . .

Output:

. R x . .
. R x . .
. R x . .
. R x . .
R x . . .

Input:

. . . . R
. . . R .
. . R . .
. R . . .
. . R . .

Output:

x . . . R
x . . R .
x . R . .
x R . . .
x . R . .

Input:

. . . . R
. . . R .
. . R . .
. R . . .
R . . . .

Output:

[nothing] or [empty/blank array/matrix]

Notes:

• Input can be in array of indexes, array of truthy/falsey values, or any other input format most comfortable to your language.
• Output should indicate the left-most valid path.
• Output can be in array of indexes, array of truthy/falsey values, or any other input format most comfortable to your language.
  • Output does not have to be in the same format as input.
  • Output nothing/(empty/blank) (array/matrix) if there is no valid path
• Standard loopholes are forbidden by default.

---

This is my first challenge, so please let me know if I have left anything out or something is unclear.

---

Related problems

• Follow incomplete directions
  • Has more obstacles, directions are given
• How varied is my obstacle course?
  • About finding paths through an obstacle course
• Grid-Routing Battle
  • Similar graph structure

I couldn't find any dupe targets looking through grid, so I'll look again in graphs and path-finding later.

Answer 2

Cypher-o-mania!

The year is 19XX.

You are a spy of some distant country, and your job is to send messages across the globe.

Unfortunately, because, frankly, you suck at being a spy, you need a way to obfuscate your information, so that when the opposition catches you (which they will), they won't know what the heck is written.

How are you going to do this?

Your task is, using two inputs (the first input the encoding "cypher" and the second the message), encode the message.

This is how the encoding works:

• The message only consists of the lowercase letters and the numerals.
• Because there are 36 different characters in total, we will convert each individual letter of the message to "base 9" (a = 00, b = 01, c = 02... 8 = 37, 9 = 38). This will be called the FSO, or First-Stage Obfuscation.
  • For example, the message hello1 would then be translated to 07 04 12 12 15 28.
• Each individual "bit" of the FSO is then stripped of its first part. This will be known as the SSO, or Second-Stage Obfuscation.
  • The example 07 04 12 12 15 28 is then translated to 7 4 2 2 5 8.
• This is where the encoder comes in handy! The encoder will consist of a string of numbers 0 to 3 (e.g. 1212003).
• You then add to the start of each digit of the encoder to the corresponding digit of the SSO. This is now the TSO, or Third-Stage Obfuscation.
  • The example 7 4 2 2 5 8 with the encoder 1212003 is then converted to 17 24 12 22 05 08.
  • With a shorter encoder (say 121), this step will "wrap around", so 7 4 2 2 5 8 with the encoder 121 will end up with 17 24 12 12 25 18.
• We then change the TSO back into readable characters, using the same "base 9" method.
  • The two examples 17 24 12 22 05 08 and 17 24 12 12 25 18 will be converted to QWLUEI and QWLLXR respectively.

So, in summary:

Encoder: 121

Message: hello1

hello1 => 07 04 12 12 15 28 => 7 4 2 2 5 8 => 17 24 12 12 25 18 => QWLLXR

This is code-golf, so shortest code in bytes wins.

META

• This is really confusing, and I don't really know how to phrase the "how the encoding works" bit better. Can anyone help me phrase this better? I can offer clarification on certain things if needed.

Answer 3

Regex golf: Match the Thu'um-s

code-golf regex

Introduction

Skyrim is a game made by Bethesda and came out in 2011. One of the objectives of the game is to collect every 27 shouts (or Thu'um-s). In this challenge, you need to match every shout and nothing else.

Shouts

This is the list of the available shouts in the game:

Raan Mir Tah
Laas Yah Nir
Mid Vur Shaan
Feim Zii Gron
Gol Hah Dov
Od Ah Viing
Hun Kaal Zoor
Lok Vah Koor
Ven Gaar Nos
Zun Haal Viik
Faas Ru Maar
Mul Qah Diiv
Joor Zah Frul
Gaan Lah Haas
Su Grah Dun
Yol Toor Shul
Fo Krah Diin
Liz Slen Nus
Kaan Drem Ov
Krii Lun Aus
Rii Vaaz Zol
Tiid Klo Ul
Strun Bah Qo
Dur Neh Viir
Zul Mey Gut
Fus Ro Dah
Wuld Nah Kest

Additionally, every shout can have 3 levels depending on what the player collected so far, each level adds a new word to each shout, so you need to be able t match the separate words without the full shout.

The words need to be uppercase. A shout should only be matched, if it is a separate word, for example: Golf shouldn't be matched.

The separate words for the same shout in the order as in the list appear next to each other, then they need to be in the same match.

The input strings will only contain ASCII letters and spaces as word separators.

Test cases

The matched text is bold

Hydrogen Sulphur Krah Coal Gaan Lah Haas

one two three four Kaal six seven Joor Zah Frul eleven

red green blue Gol Hah orange purple Qo violet

Ran Miir Taah Raan Mir Tah raan mir tah

Golf Gol Middleage Mid

Rules

• The answer should be a .NET type RegEx and should not contain any other langauge.

• This is a code-golf, so the shortest answer in bytes wins

Answer 4

Find all the Vampire numbers

Shamelessly stolen from https://stackoverflow.com/q/17352108

A "Vampire" number is defined as the product of two numbers of equal length (known as the "fangs") that uses the same digits as the two numbers being multiplied. Examples:

21 * 60 = 1260
15 * 93 = 1395
30 * 51 = 1530

Your task is to find all the Vampire numbers whose fangs have n digits.

This is code-golf, so the shortest solution wins.

Answer 5

Title TBD - Generate Emoticons :)

code-golf kolmogov-complexity

Your task is to create a program that generates the most emoticons using the least amount of code.

Rules

• The only valid emoticons are listed on Wikipedia, under the heading Western/horizontal emoticons: List of emoticons page (version 722951221)
• The output can be any format, as long as a delimiter exists between emoticons.

Scoring

• Scores will reflect the character (not byte) count.
• For every emoticon after 10 that is output by your program, subtract 1 from your score. Emoticons over 20, subtract 2, over 30 subtract 3, and so on.

Sandbox

Is the scoring fair/reasonable? Should I edit down the list/create a new list of acceptable emoticons?

Answer 6

Forecast Romantic Dates

code-golf date

Sort of inspired by this.

A Romantic date is a date that, when the year, month and day are converted to Roman Numerals the individual values contain no more than two symbols. For example, in YY-MM-DD format: the Romantic date 20-04-15 would become XX-IV-XV.

For the purpose of this challenge, years will only be tracked by the two least significant digits of the year, as otherwise the last Romantic date was in the 15th century. In addition, they wouldn't add much to the challenge as the omissions of the leap year every 400 years is irrelevant, as February the 29th is not a Romantic date.

Romantic dates

For your convenience, here is a list of all of the two digit numbers that can be represented with two or fewer symbols in Roman numerals:

[1, 2, 4, 5, 6, 9, 10, 11, 15, 20, 40, 50, 51, 55, 60]

These were determined using the "standard method" that negative groups would only be used with the symbols that are powers of ten and only on the values that are five or ten times that symbol's value. So I only combines with V and X for example.

Dates which include only numbers from this list are Romantic dates. For the purpose of this challenge, assume an ideal Western calendar: no dates are ever skipped or repeated, 12 months per year, and more than 20 days per month. Assume there is no year, month or day zero (i.e. year 99 loops to 1 not to 0).

Task

Given a date as input, output that date if it is Romantic, or output the next Romantic date.

Input and Output

You may accept input in any consistent ordering of year, month and day with any consistent separator. You may specify if the input should have the numbers padded to be two digits. If the numbers are padded, you may choose to have no separator. Your output must have the same form as your input.

Test Cases

The following test cases are all in the format YY MM DD, with no padding.

1 1 1 => 1 1 1
20 4 3 => 20 4 4
15 7 1 => 15 9 1
51 9 7 => 51 9 9
70 9 7 => 1 1 1
20 6 24 => 20 9 1
47 12 1 => 50 1 1
60 11 24 => 1 1 1

Here is the script that I used to generate these.

Sandbox

Did I miss any Romantic numbers? I just did that by hand.

Allow unary? I'm unsure about this because it sort of violates the reasoning behind Romantic dates for the values to have >2 symbols...

Should I explain more about parts of dates that are not useful? For example, the length of the months is entirely irrelevant as the later days are all skipped. My concern is that the current one feels clunky already

Should I allow both outputting the input if the date is already Romantic or the strictly next Romantic date (as long as it is consistent)? There doesn't seem to be much different, but I don't know if that'd be too broad? Personally leading towards allowing it.

I'm also somewhat tempted to make use of the silly title a bit more, but I'm not sure if that'd be going overboard.

Too boring / compression based? I've particularly been trying to think of a way for fewer results to wrap back around to 1.

Answer 7

Stacks and Stacks and Stacks...

Write a program that, with the input as n, finds the first n-gonal and n-gonal pyramid number that is NOT 1.

n is guaranteed to be larger than or equal to 3.

Examples:

• n = 3: 10
• n = 4: 4900
• n = 2: The output can be nothing, False, or anything that you want, just as long as it can be distinguished from an actual output.

This is code-golf, so shortest code in bytes wins.

Bonus:

• If your code output both the name of the n-gon and the number: You get a big fat -50% off of your byte count (see below for examples).
  • n = 4: Square 4900
  • n = 3: Triangle 10
  • n = 5: Pentagon ??? (the ??? is a placeholder because I have no idea what the number is)

Meta:

• Is the bonus a good idea?

Answer 8

Pyth Meta-Golf Golf Battery

metagolf test-battery code-challenge

(now that's a name, isn't it?)

The Challenge

Write a program in a language of your choice that takes an input of code in the same language and outputs a code that does the same thing in Pyth (though not necessarily the shortest code).

Rules

Given the test battery set below, you should try to find the best way to minimize your score with the following rules:

• You must minimize the source code of the submission.
  • You may not used compressed versions of the input source for each test; the Pyth code must be output procedurally.
  • The code must theoretically do the same conversion for any input code, not necessarily just these test cases.
• You must minimize the input code of each test.
  • If an input is shown to be shortenable by without non-standard libraries of the submitted language, you must change it immediately to the shorter answer. If your answer does not support this change, then you must change your answer to accommodate.
• You may not submit answers written in Pyth.

Scoring is done with the following equation:

(source code)*((Pyth src out, test 1)/(input src in, test 1)+(same for test 2)+...)

Objectives of each test

Test 1:

Output the string "Hello, world!".

Test 2:

Given an integer input, multiply that input by three and output it.

Test 3:

Quine. (must be a valid quine in the submitted language and in Pyth)

Test 4:

Produce infinite output.

Test 5:

Cat program.

Answer 9

Don't even think about non-42-related numbers!

code-golf math fibonacci

---

Introduction and Credit

We all love our Answer to the Ultimate Question of Life, the Universe, and Everything which, of course is 42. So let's take this unworthy Fibonacci-Sequence thingy and adapt it to be worthy of 42!

Specification

Input

The input will be a positive integer.

Output

The output will be either true or false.

What to do?

Your task is to implement the predicate that the number under consideration is an element of the generalized Fibonacci-Sequence given by:

a_1 = 14
a_2 = 42
a_n = 41 * a_{n-1} + 43 * a_{n-2}

Where 42 is the ultimate answer, 41 and 43 are the primes next to it and 14 is the preceding catalan number.

Potential corner cases

The number will always be greater than zero. Your program must pass all (32-bit) test vectors below.

Who wins?

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

Test Vectors

14 -> true
42 -> true
2324 -> true
4080622 -> true
97090 -> true
171480372 -> true
7 -> false
1 -> false
41 -> false
43 -> false

Answer 10

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.

Additional Rules!

• 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

Answer 11

Generate a random Vietnamese syllable

tags: code-golf random

---

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.

Answer 12

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

Answer 13

nth number that multiplies k equals its reverse

Tags: code-golfing,math

---

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.

Answer 14

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.

Answer 15

Reinventing the Modularization Wheel

code-golf

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!

Answer 16

Print a Pilcrow Scarecrow

Print the following ascii scarecrow using the pilcrow character ¶

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

• Padding must be with (space) and built with ¶
• Trailing padding is okay
• Print to stdout
• This is code-golf

---

code-golf ascii-art kolmogorov-complexity

Answer 17

It's time to unify!

code-golf logic math

---

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:
Let [("f",2),("g",2),("a",0),("b",0)] be your functions
[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)
[]

Answer 18

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.

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• 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

Answer 19

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

Answer 20

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.

Answer 21

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!

code-golfrestricted-sourcemath

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I seriously have no idea how to make test cases for this.

Answer 22

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 code-golf, so the shortest solution wins.

Answer 23

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.

code-golf music

Answer 24

This will be a code-golf challenge. Additional tags are internet, date and math.

How fast is your Stack Exchange community?

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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 code-golf so shortest answer in bytes wins.
• Standard loopholes are disallowed.
• Leading/trailing whitespaces/newlines are fine.

Answer 25

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

Answer 26

Do I have an emoji?

code-golf string

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

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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?

Answer 27

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.)

Answer 28

Reverse stdin to stdout, Unicode aware and by grapheme clusters

It's 2016. High time that we were Unicode-aware, don't you think?

Given a UTF-8 string on stdin, reverse it by extended grapheme clusters (as defined by the Unicode consortium; this can be found here, for instance) and place it on stdout. This is seemingly a trivial challenge, but surprisingly difficult in many languages.

You may not use an explicit end-of-file character - if supported, use EOF. If not supported, use an explicit length at the start of the string, and document the format.

Note that the string may be of any length (barring RAM limitations).

You must handle direction override characters "properly", in the sense that the directionality of every character must remain the same after reversing the string.

Answer 29

Given an ordinal A and a nonnegative integer B, compute f_A(B)

A will be expressed in Cantor Normal Form. A number is in Cantor Normal Form if it is 1, or if it is either of the form a+b or w^a, where a and b are in Cantor Normal Form, and w is the ordinal omega.

f_A(B) is the fast-growing hierarchy, specifically, the Wainer Hierarchy. f_0(n)=n+1. f_(a+1)(n)= n iterations of f_a to n. f_a(n)=f_an if a is a limit ordinal. a[n] is the nth member of the fundamental sequence for a.

Answer 30

code-golf number

Difficulty Naming

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Introduction

In the game osu!, players can make their own beatmaps (levels). The harder the beatmap is, the bigger the star rating will be.

Beatmaps have star icons with different colors and letters according to their star rating.

osu! has also four game modes. The shape of the icon will change depending on the game mode.

The Challenge

Given a star rating and a gamemode, output the (generally used) difficulty name.

The Input

• A positive floating-point number (star rating)
  • You can assume the number will never have more than two decimal places.
• A positive integer (game mode)
  • 1 is Standard, 2 is Taiko, 3 is Catch the Beat and 4 is Mania (you can use other numbers for the game modes, these are the default.)

The Output

• A string (difficulty name)

Use this table to determine the output:

diff table http://image.prntscr.com/image/174e34e56dbb40ad81b209fac3fdc5bc.png

(if the star rating is exactly 5.25, it counts as Above 5.25)

Rules

• This is code-golf, so the shortest solution wins.
• Standard loopholes are disallowed.
• You can take the input either as an array/list, a string separated by commas or spaces, or each number individually.
• Again, you can use other numbers for the game modes.

Test Cases

2.24, 2 ---> Futsuu
1.1, 4 ---> Basic
3.14, 1 ---> Hard
7.0, 3 ---> Overdose
5.0, 4 ---> Exhaust
31415.0, 2 ---> Ura Oni
0.01, 1 ---> Easy
5.25, 1 ---> Expert

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Sandbox

If you see any grammar errors or anything like that, please tell me, I'm not a native speaker.