Sandbox for Proposed Challenges

Question

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

Sandbox FAQ

Posting

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

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

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

Discussion

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

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

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

If you think one of your posts requires more feedback, but it's been ignored, you can ask for feedback in The Nineteenth Byte. It's not only allowed, but highly recommended! Be patient and try not to nag people though, you might have to ask multiple times.

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

Other

Search the sandbox / Browse your pending proposals

The sandbox works best if you sort posts by active.

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

Answer 1

Draw the Progress Pride flag

Answer 2

Draw this fractal generated by applying Newton's method to cosh(x) - 1

Answer 3

Implement Binary Exponentiation

Answer 4

Is it an ordinal?

Answer 5

Draw the USA flag

Answer 6

Convert from Greeklish to modern Greek

Answer 7

Solve a Card Suit Puzzle

Answer 8

Every possible pairing

Answer 9

Infinite Fibonacci word code-golf sequence fibonacci string

The famous Fibonacci sequence of integers is defined as follows:

\$ F_0 = 0 \\ F_1 = 1 \\ F_n = F_{n-1} + F_{n-2} \$

But what if we use this same recurrence relation to produce an infinite sequence of strings? Instead of addition, we'll use concatenation. We'll also change the base case slightly:

\$ F_0 = \$ 0
\$ F_1 = \$ 01
\$ F_n = F_{n-1}F_{n-2} \$

The first few strings are:

0
01
010
01001
01001010
0100101001001
...

Each of these "words" is a prefix of the next, so they are all prefixes of the single infinite word \$ F_\infty = \$

010010100100101001010010010100100101001010010010100101001001010010010100101001001010010010100101001...

Your task is to output this infinite string as a sequence; you may choose to use any two distinct values to use for 0 and 1.

As with standard sequence challenges, you may choose to either:

• Take an input \$ n \$ and output the \$ n \$th item in the sequence
• Take an input \$ n \$ and output the first \$ n \$ item
• Output the sequence indefinitely, e.g. using a generator

and you may use 0-based or 1-based indexing for \$ n \$.

This string can be defined in many different ways; its OEIS entry A003849 and Wikipedia page have more information.

Errors due to floating-point imprecision are not allowed.

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

Answer 10

All Crossword Grids

code-golf crossword grid

In crossword terminology, the grid is the region into which the crossword answers are inserted, consisting of white and black squares. The crossword answers, called entries, are inserted into contiguous sequences of white squares in a row or column, separated by black squares.

For straight (American) crosswords, the grids usually follow a specific set of rules:

• They should have 180 degree rotational symmetry (if there is a black square in the \$x\$th row and \$y\$th column, there should be a black square in the \$x\$th-to-last row and \$y\$th-to-last column).
• All entries must be at least 3 squares long.
• All white squares must be joined in a single region.
• No row/column can be completely filled with black squares.

Some examples of invalid and valid crossword grids:

Your challenge: given a grid consisting of two unique values representing black and white squares, determine if it's a valid crossword grid. Assume that it's a square grid with \$n\$ rows and columns (so there are \$n^2\$ white/black cells), where \$n \geq 3\$. For example, if \$n=3\$ there is only one valid grid (I'm using . for white cells and # for black cells):

...
...
...

If \$n=4\$, there are 3 valid grids:

....  #...  ...#
....  ....  ....
....  ....  ....
....  ...#  #...

If \$n=5\$, there are 12 valid grids:

.....  #....  ##...  #....  ##...  ##...  
.....  .....  .....  #....  #....  ##...  
.....  .....  .....  .....  .....  .....  
.....  .....  .....  ....#  ....#  ...##  
.....  ....#  ...##  ....#  ...##  ...##  

....#  ...##  ....#  ...##  ...##  #...#  
.....  .....  ....#  ....#  ...##  .....  
.....  .....  .....  .....  .....  .....  
.....  .....  #....  #....  ##...  .....  
#....  ##...  #....  ##...  ##...  #...#  

Examples:

Input	Output	Explanation
.........	True	Valid grid
#..............#	True	Valid grid
...#........#...	True	Valid grid
...#........#...	True	Valid grid
.........	True	Valid grid
#...#......#...#	True	Valid grid
.........................	True	Valid grid
##...#.............#...##	True	Valid grid
.................................................	True	Valid grid
........................#........................	True	Valid grid
....###.....##......##.....##......##.....###....	True	Valid grid
................................................................	True	Valid grid
##....####....##...........##......##...........##....####....##	True	Valid grid
...##.......#...........##.....##.....##...........#.......##...	True	Valid grid
#...............	False	No 180 degree symmetry
#..##..##..##..#	False	2-letter entries, filled-in columns
#........................	False	No 180 degree symmetry
.......#...###...#.......	False	1-letter and 1-letter entries
######....#....#....#....	False	No 180 degree symmetry, filled-in column & row
######...##...##...######	False	Filled-in columns & rows
...#......#......#......#......#......#......#...	False	White squares not contiguous, filled-in column
.................###....#....###.................	False	1-letter entries
...#......#...............##.....................	False	No 180-degree symmetry
....#.......#.......#........######........#.......#.......#....	False	White squares not contiguous
..#.........#.......#......##......#.......#.......#.........#..	False	1-letter and 2-letter entries
.#......#..............................................#......#.	False	1-letter entries, white squares not contiguous
...........................##......#............................	False	No 180-degree symmetry
####............................................................	False	No 180-degree symmetry
#......##......##......##......##......##......##......##......#	False	Filled-in columns

Standard loopholes are forbidden. Shortest code wins.

Sandbox Questions

I may have misused some crossword terminology above, let me know if I can improve the explanation.

I also don't know if the final rule should be included, since it's not usually explicitly stated when constructing crosswords.

I'm considering adding an optional parameter \$n\$ which describes the number of rows/columns to make the input easier to parse, but I don't know how people feel about optional parameters.

Answer 11

Add parentheses to Polish notation

Answer 12

Change The Quotations as if in Microsoft Word

META: Posted

Answer 13

Carry-less sum given a base b

posted

Answer 14

code-golf decision-problem

Are these numbers from the repeated application of this function?

Given a list of at least 3 positive integers \$L\$ and a function \$F\$ which takes a positive integer and returns a positive integer, determine if \$L\$ can be sorted such that each element of the list is the result of applying \$F\$ to the previous element (besides the first of course).

Rules

• You may, of course, assume that \$F\$ always halts.
• You may also assume that \$F\$ will have no side-effects and is deterministic.
• You may take the \$F\$ as a black box function in any reasonable format.
• Instead of taking \$F\$ as an input, you may take a second list \$M\$, which is the result of applying \$F\$ to each element of \$L\$.
• This is code-golf, shortest solution in bytes wins.

Very simple worked out example

Inputting \$F(x)=x+1\$ and \$L=[5,4,3,2,1]\$ should output truthy, because \$L\$ can be rearranged into \$[1,2,3,4,5]\$, for which each element is the result of applying \$F\$ to the previous element: \$F(1)=2\$, \$F(2)=3\$, \$F(3)=4\$, and \$F(4)=5\$.

More examples:

Truthy

F(x) = 2x,           L = [4,2,1,8]
F(x) = ceil(10/x),   L = [2,2,2,5,5,5]
F(X) = 3x+1,         L = [5,16,49,148]
F(x) = length(x),    L = [1,2,10,9876543210,1]
F(x) = 13            L = [13,13,13,13,14]

Falsy

F(x) = 2x,           L = [2,4,6,8]
F(x) = ceil(10/x),   L = [5,2,5,2,5,2,5,5]
F(X) = 3x+1,         L = [5,16,8,4,2,1,4]
F(x) = length(x),    L = [3,1,10,2]
F(x) = 13            L = [13,13,13,14,15]

META

Is this ready to post or is it missing something / bad somewhere

Answer 15

Implement level-index addition

Answer 16

answer-chaining king-of-the-hill

This is less of a challenge proposal, and more of a idea for how to mesh the two title tags.

A series of targeted fights

Consider a heads-up, 1v1 "game" between two king-of-the-hill style bots. However, unlike a general king-of-the-hill, where every bot plays against every other bot, we instead build bots that target specific bots to win against. An example of an existing bot would be Low Blow from Cooperative Counting, which aimed to identify it's opponent, then play counter to that bot. However, in this challenge, the bot wouldn't have to identify its opponent: it would only play one bot, the bot it was designed to beat.

The answer-chaining aspect comes from this targeting:

• User A posts Bot A, targeting a provided example bot.
• User B then posts Bot B, targeting Bot A.
• User C then posts Bot C, targeting a second example bot.
• User D then posts Bot D, also targeting Bot A.

And so on, creating a "tree" of answers, each targeting a previous answer. Note that new answers don't have to target the latest, but can instead target any previous answer.

However, to prevent bots that "target", but don't actual perform well against their target, we'd need to require that it beats its target in \$X\%\$ of \$Y\$ battles, or else it is disqualified. Obviously, this prevents bots from being edited to improve themselves once targeted.

This begs the question: what is our scoring criteria? Clearly, depth from the root bots (provided in the challenge) must be a central part, as it's harder to create a bot the further down the chain you go. However, this doesn't differentiate between Bot B and Bot D in our example, despite the fact that Bot D beats Bot A \$82\%\$ of the time, vs Bot B's meager win rate of \$61\%\$. Clearly, we should take winning rate into account. One potential score:

$$\text{Score} = \text{Win rate} \times \text{Depth}$$

where \$\text{Win rate}\$ is between \$0\$ (never wins) and \$1\$ (always wins).

---

Thoughts?

Answer 17

write the "index by number" sequence

Imagine writing out positive integer numbers, and indexing each character in a 1-indexed array (indices read vertically on the top two rows, numbers read horizontally on the third):

000000000111111111122222222223333333333444444444
123456789012345678901234567890123456789012345678
one two three four five six seven eight nine ten

Now, imagine if we skipped some numbers so we write the index at the point we start the next number:

000000000111111111122222222223333333333444444444
123456789012345678901234567890123456789012345678
one five ten fourteen twenty three thirty six fo

now, imagine that the first number doesn't have to be "one":

000000000111111111122222222223333333333444444444
123456789012345678901234567890123456789012345678
      seven thirteen twenty two thirty three for

Input

A single number from 1..999, in any format you like ("1", '1', 1, "one" etc.)

This forms the starting number for the sequence

Output

A sequence of numbers, written long-hand in UK English ("one hundred and one" - no other differences), from (input)..(999) inclusive.

Code golf, usual rules.

Answer 18

Generate a different sudoku

code-golfsudokugridopen-ended-function

---

Task

Given a valid sudoku board, generate another sudoku board that isn't equivalent to the one inputted.

What do we consider as equivalent sudoku boards?

• they are the same,
• the digits are relabeled (eg. 2<->7 or 2->5->8->2),
• three-column or thee-row bands are permuted,
• the rows or columns within a band are permuted,
• one is a reflection of the other (horizontally, vertically or along any of the diagonals),
• one is a rotation of the other,
• or any combination of the above.

According to Ed Russell and Frazer Jarvis there are 5 472 730 538 essentially different sudoku classes.

What is a valid sudoku?

(borrowed from here)

• Each row contains the digits from 1 to 9 exactly once.
• Each column contains the digits from 1 to 9 exactly once.
• Each of the nine 3x3 subgrids contains the digits from 1 to 9 exactly once.

Rules

You may take input and output in any reasonable format, like a 9x9 matrix, list of rows/columns, a string of 81 digits etc.

Taking digits 0-8 instead of 1-9 is allowed, but please be consistent.

Test cases

Input:
7 2 5 8 9 3 4 6 1
8 4 1 6 5 7 3 9 2
3 9 6 1 4 2 7 5 8
4 7 3 5 1 6 8 2 9
1 6 8 4 2 9 5 3 7
9 5 2 3 7 8 1 4 6
2 3 4 7 6 1 9 8 5
6 8 7 9 3 5 2 1 4
5 1 9 2 8 4 6 7 3
Example output:
1 2 3 4 5 6 7 8 9 
4 5 6 7 8 9 1 2 3 
7 8 9 1 2 3 4 5 6 
2 3 1 5 6 4 8 9 7 
5 6 4 8 9 7 2 3 1
8 9 7 2 3 1 5 6 4 
3 1 2 6 4 5 9 7 8
6 4 5 9 7 8 3 1 2 
9 7 8 3 1 2 6 4 5

Input:

Example output:

Meta

• Any mistakes in the test-cases?
• Is it sufficiently diffent to existing sudoku challenges?
• Is it better as open-ended-function or a challenge to check whether two given grids are equivalent?

Answer 19

Print every Fool's Mate

Answer 20

open-ended-function code-golf

N-element Rock Paper Scissors

Given an odd integer \$n>2\$, decide the winner for \$n\$-element Rock Paper Scissors.

What is \$n\$-element Rock Paper Scissors?

Rock Paper Scissors is a game in which two players choose between the elements Rock, Paper, and Scissors, and simultaneously reveal their selections. If one player chooses Rock, they will win against a player who chose Scissors, lose against a player who choses Paper, and tie a player who also chose Rock. It is a zero sum game, so a player losing means their opponent has won, and vice versa. Every element beats one element, loses to another, and ties with itself.

A common extension to this game is to add two aditional elements (most famously "Lizard" and "Spock"). In this extension, there are now 5 elements, so each element beats two elements, loses to two elements, but still ties only itself. We can generalize this cleanly to any odd number of elements \$n\$, in which each element will beat \$(n-1)/2\$ elements, lose to \$(n-1)/2\$ elements, and tie with itself.

Challenge specification

Program 1

This program should take an odd integer \$n>2\$ as input in any reasonable format decided by the solver, and output the Program 2 as defined below in terms of \$n\$. Alternatively, this program may instead take the Program 2's inputs along with \$n\$, and provide the Program 2's expected output instead.

This program is the one you will be scored on. This is code-golf, so shortest code in bytes wins.

Program 2

This program should take two elements \$A\$ and \$B\$ as input in any reasonable format decided by the solver, and consistently output either one of the following:

• Whether \$A\$ beats \$B\$, loses to \$B\$, or ties with \$B\$.
• The winner between \$A\$ and \$B\$, or in the case of a tie, some other distinct output.

Only \$n\$ possible inputs need to be handled by this program. Each possible element must consistently beat \$(n-1)/2\$ elements, lose to \$(n-1)/2\$ elements, and tie with itself. If some element \$a\$ beats an element \$b\$, element \$b\$ loses to element \$a\$. Which elements are allowed and which elements beat which etc. are to be decided by the solver. This must be consistent for each execution of Program 2 for the same \$n\$

Examples:

Your I/O may differ.

Format:
n (input to Program 1)
a b c d e (list of inputs accepted by Program 2, space delimited for all examples)
x y (inputs to Program 2, space delimited for all examples)
value (whether x wins, loses, or ties y)

3
r p s
r p
lose

3
r p s
r r
tie

3
r p s
r s
win

5
0 1 2 3 4
0 1
win

5
0 1 2 3 4
0 2
win

5
0 1 2 3 4
0 3
lose

5
0 1 2 3 4
0 4
lose

5
abcde bcdea cdeab deabc eabcd
bcdea cdeab
lose

5
abcde bcdea cdeab deabc eabcd
bcdea deabc
lose

5
abcde bcdea cdeab deabc eabcd
bcdea eabcd
win

5
abcde bcdea cdeab deabc eabcd
bcdea abcde
win

5
abcde bcdea cdeab deabc eabcd
bcdea bcdea
tie

13
a b c d e f g h i j k l m
g e
lose

13
a b c d e f g h i j k l m
g m
win

13
a b c d e f g h i j k l m
d h
win

13
a b c d e f g h i j k l m
h d
lose

Meta

Everything clear? Any other examples needed? Maybe a worked out example?

Answer 21

Repeat Values In Array

Answer 22

Abbreviate the inputted phrases

Given an ASCII string, replace all occurrences of " is ", " are ", " am ", and " have " with "'s ", "'re ", and "'ve " respectively. This must be done case insensitively.

Examples

Input	Output
I am	I'm
She is	She's
The dog is	The dog's
I have a dog	I've a dog
I have been hurt	I've been hurt
Wadsfajsdfl have asdasd	Wadsfajsdfl've asdasd
So, is 6 am fare	So,'s 6'm fare
foo amxyz	foo amxyz
have I	have I
HAVE I	HAVE I
I HAVE	I've
I AM	I'm
I haven't	I'ven't
ambc xisz	ambc xisz

Answer 23

Make a Court Transcriber

Answer 24

Partial Fractions

Answer 25

Infinite Integer Derivative code-golf

We can consider the derivative of a integer sequence to simply be the difference between each element and the next:

1  5  8  13  2
 4  3  5  -11

Note this will produce a sequence one shorter than the original. We can repeat this process to find the second derivative:

-1 2 -16

And continue this process till there is one element left.

Conjecture A sequence of length n can be exactly represented by first element of each integer derivative. We call this the infinite integer derivative.

Example:

              [8   4  12   6  3]
8              [-4  8   -6  -3]
8 -4             [12 -14  3]
8 -4 12           [-26  11]
8 -4 12 -26          [37]
8 -4 12 -26 37

Example python code:

f = lambda x:x and [x[0]]+f([x[i]-x[i-1] for i in range(1,len(x))])

Note there may be more efficient ways to compute values than this formula.

Test cases

{
    [1,2,3,4,5]:    [1,1,0,0,0],
    [1,2,1,2,1]:    [1,1,-2,4,8],
    [1,2,4,8,16]:   [1,1,1,1,1],
    [5,1,-1,0,6,3]: [5,-4,2,1,1,-17],
    []:             [],
    [12]:           [12],
    [5,5,5,5,5,4]:  [5,0,0,0,-1],
    [5,4]:          [5,-1]
}

Answer 26

Prime factor power sorting

Background

We will introduce a new way of writing numbers where the digits represent powers of primes starting with the largest prime factor of the number, and ending with the power of 2 in the prime factorization. As an example, 2 = 2¹, so it would be written as 1. Slightly more complicated, 3 = 3¹ * 2⁰, so it is written as 1 0. Here's a few more:

6:     1 1
7: 1 0 0 0
8:       3
9:     2 0
10:  1 0 1

So the place value of the n'th "digit" is the n'th prime number, and the digit itself represents the power of that prime in the factorization of the number. 1 is encoded simply as or 0 (the choice does not affect comparison).

The Challenge

We can compare numbers in this form by first examining how many digits it has, and then breaking ties by comparing the digits themselves like normal. For instance, any power of 2 has only one digit, and so 2ⁿ < 3 for all n because 3's prime power representation has two digits. However, when numbers have the same length (meaning their highest prime factors are equal) we compare the lists of digits element-wise. Therefore 12 < 9 because 12th = 1 2 and 9 = 2 0.

Your challenge is to write a function or program which takes as input a collection of distinct integers greater than or equal to 1, and outputs the same collection sorted this way in ascending order. This is code golf, so the score is the length of your solution in bytes.

Examples:

I have written an example solution (Try it online!) which generates the following examples with the input and output separated by a colon:

1 2 3 4 5: 1 2 4 3 5
2 4 8 16 32 64 3: 2 4 8 16 32 64 3
1 3 5 7 9 11 13 15: 1 3 9 5 15 7 11 13
40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55: 48 54 40 45 50 42 49 44 55 52 51 46 41 43 47 53
1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019: 1000 1008 1001 1014 1012 1015 1007 1003 1005 1010 1017 1016 1002 1004 1011 1006 1018 1009 1013 1019
 

Answer 27

Triangular honeycomb numbers

Answer 28

Box blur the string

Answer 29

Conversions Galore!

Answer 30

Generate the Sequence of Equivalence Relations (OEIS A231428)

code-golf sequences binary-matrix

Introduction

An equivalence relation \$R\$ on a set \$S\$ is

• reflexive: \$ \forall a\in S: aRa\$
• symmetric: \$ \forall a,b \in S: aRb \leftrightarrow bRa \$
• transitive: \$ \forall a,b,c \in S: aRb \wedge bRc \rightarrow aRc \$

These relations can be represented as boolean matrices where:

• reflexive: the diagonal is all ones
• symmetric: the entries are symmetric over the diagonal (\$a_{ij}=a_{ji}\$)
• transitive: the matrix, when pairs of rows and the corresponding pairs of columns are suitably swapped, consists of entirely-1 and entirely-zero blocks, with the on-diagonal blocks entirely-1.

Here are a few such matrices:

1 0        1 1 0 0 0        1 0 1 0       can swap rows     1 1 0 0
0 1        1 1 0 0 0        0 1 0 1  -->  2&3, columns  --> 1 1 0 0
           0 0 1 1 1        1 0 1 0       2&3 to obtain:    0 0 1 1
           0 0 1 1 1        0 1 0 1                         0 0 1 1
           0 0 1 1 1

Making use of the reflexive and symmetric properties, we can encode such a matrix by concatenating the rows of its upper-right triangle, and converting from binary to decimal. (The example matrices encode as 0b0=0, 0b10 0000 0111=519, 0b01 0010=18, and 0b10 0001=33.)

Challenge

Write a program or function that outputs all equivalence relations in order (as encoded above). Default sequence rules apply, so you can output an unbounded list, you can take an input \$n\$ and return the \$n^{th}\$ term, or you can take an input \$n\$ and return the first \$n\$ terms. Default Loopholes forbidden. This is code-golf, so shortest program wins.

For reference, the first 25 terms of this sequence are

0, 1, 2, 4, 7, 8, 12, 16, 18, 25, 32, 33, 42, 52, 63, 64, 68, 80, 96, 116, 128, 130, 136, 160, 170

Here are example matrices which generate the first few terms of the sequence:

A: 1 0 0     
   0 1 0    0b000 -> 0    
   0 0 1     
          
B: 1 0 0 0
   0 1 0 0    0b00 0000 0001 -> 1    (also: 1 1 among others)
   0 0 1 1                                  1 1 
   0 0 1 1

C: 1 0 0 0 0
   0 1 0 0 0
   0 0 1 0 1    0b00 0000 0010 -> 2
   0 0 0 1 0
   0 0 1 0 1

D: 1 0 0 0 0
   0 1 0 0 0
   0 0 1 1 0    0b00 0000 0100 -> 4
   0 0 1 1 0
   0 0 0 0 1

E: 1 1 1
   1 1 1    0b111 -> 7
   1 1 1

F: 1 0 0 1
   0 1 0 0    0b00 1000 -> 8
   0 0 1 0
   1 0 0 1

G: 1 0 0 0 0
   0 1 0 0 1
   0 0 1 1 0    0b00 0000 1100 -> 12
   0 0 1 1 0
   0 1 0 0 1

Sandbox notes

related: Is This an Equivalence Relation?, Determine if a relation is transitive

My first try, so please don't be shy about suggesting improvements, making edits, heckling... I can take it =)