# Sandbox for Proposed Challenges

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

Sandbox FAQ

## Posting

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
• 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".

Get the Sandbox Viewer to view the sandbox more easily!

# Convert Klingon romanization to pIqaDcode-golf

## Context

Klingon is a constructed language from Star Trek. It has two writing systems: a not-very-good Latin alphabet (with case distinctions, I being different from l, ...) and its own script, called pIqaD.

Convert the bad[disputed - discuss] Klingon romanization into pIqaD. Here's a CSV (the pIqaD [or, if you don't have a font for it, boxes or nothing] is in the second column and the Unicode hexadecimal codes are in the third):

a,,f8d0
b,,f8d1
ch,,f8d2
D,,f8d3
e,,f8d4
gh,,f8d5
H,,f8d6
I,,f8d7
j,,f8d8
l,,f8d9
m,,f8da
n,,f8db
ng,,f8dc
o,,f8dd
p,,f8de
q,,f8df
Q,,f8e0
r,,f8e1
S,,f8e2
t,,f8e3
tlh,,f8e4
u,,f8e5
v,,f8e6
w,,f8e7
y,,f8e8
',,f8e9


Be careful not to mix up q and Q, they are different letters in Klingon!

## Input and output

Strings! or your language's equivalent. You can assume that the input contains no characters not in Klingon (incl. miscapitalized dhis) or numbers or punctuation.

# Scoring

Lowest byte count wins, as always.

suggestions? :)

• I like it! It seems ready for publication. May 25, 2022 at 21:34
• My browser shows only ⍰ in the second column of the csv. Maybe add a link to TIO or other external page, which will render it correctly. If possible, you may also add UTF codes for those characters. May 26, 2022 at 10:02
• @pajonk i added the unicode codes :)
– matt
May 29, 2022 at 14:28

# Generate Fibonacci Primes Quickly

Unsurprisingly, fibonacci primes are primes that are also Fibonacci numbers. There are currently 34 known Fibonacci primes and an additional 15 probable Fibonacci primes. For the purpose of this challenge, the Fibonacci numbers are the sequence $$\F_n\$$ defined as $$\F_1 = 1\$$, $$\F_2 = 1\$$, and $$\F_n = F_{n-1} + F_{n-2}\$$, and a number is considered prime if it passes a probabilistic prime test with a probability of being incorrect of less than $$\2^{-32}\$$. For example, since a $$\k\$$ round Miller-Rabin test has an error probability of $$\4^{-k}\$$, a 16 round Miller-Rabin test is sufficient to prove primality for the purpose of this challenge.

## Submissions:

The goal of this challenge is to write a full program that calculates every Fibonacci prime and its index in the Fibonacci series as fast as possible.

Submissions shall be a full program, complete with instructions for building and running it. Submissions must be in a language freely available for noncommercial use and capable of running on Windows 10, and users must be prepared to provide installation instructions for that language. External libraries are permitted, with the same caveats that apply to languages.

Primes will be output by writing to stdout with a simple binary format, that has a little-endian byte order:

[8 bytes- index into the Fibonacci series]
[8 bytes- length of the Fibonacci prime, in bytes]
[? bytes- the Fibonacci prime, as a byte array]


## Scoring

The programs will be run on an Intel(R) Core(TM) i5-8365U CPU with 8 threads, avx-2 support, and 24 Gigabytes of ram. The largest prime that can be correctly reached in one minute wins. Tiebreaker is the time taken to reach the largest value. Programs that tamper with my computer or the testing program will be disqualified. Programs that error or otherwise fail to produce the correct output will be judged based on the furthest Fibonacci prime reached before they failed.

The test program can be found here. Additionally, there is an example program here.

## Meta

The test program is now completed and posted, but I still have a little documentation to write. I chose the output format to be simple, and so that answers wouldn't have to worry about formatting integers quickly. Is there anything I need to improve clarity-wise?

• Since there are only 34 (?+15) of them, how will you stop a program from hard-coding these, and then starting looking for larger ones from the last of them onwards? May 22, 2022 at 10:02
• @DominicvanEssen tweaked the question to use "calculate" instead of "list", which has worked for other challenges in the past. I also posted the controller. May 30, 2022 at 5:30
• How is the "error bound" of a "probable prime" defined? May 30, 2022 at 15:07
• @pxeger I hopefully clarified what I meant, by error bound I meant error probability. May 30, 2022 at 17:01

# lol is an ambigram, dad isn't

• I think you mean "rotated", not "reversed". Related, Related, but not a dupe of either. May 30, 2022 at 5:20
• I think using the word "palindrome" is misleading here. Palindrome is specifically for reversing right-to-left, not rotating. Also, please specify what kind of rotation is required (180 deg around the center of the word, isn't it?) and add some longer test-cases with various length. Please also specify what to do with empty string. Suggestion: make this decision-problem, not a "filter a list", because now it requires some needless boring boilerplate code. May 30, 2022 at 10:08
• I've edited this down to a stub now that it's been posted to save space Jun 4, 2022 at 2:50

# How much more to a repdigit?

• These are more commonly referred to as repdigits Jun 4, 2022 at 17:55

# Enumerate all pure sets

• sequence IO? Jun 12, 2022 at 9:05
• @pxeger Good idea :P Jun 12, 2022 at 9:13

# Interpret BigTalk

Talk is a language which takes a single bit of input and has four commands:

• 00 If the accumulator is 0, set the accumulator to 0.
• 01 If the accumulator is 0, set the accumulator to 1.
• 10 If the accumulator is 1, set the accumulator to 0.
• 11 If the accumulator is 1, set the accumulator to 1.

These can be interpreted as replacement commands. We're going to extend that concept to positive integers, and make the language more complicated.

The language we're going to be defining is called BigTalk. It has an accumulator, which is a list of positive integers, initially set to only the input.

Programs are a series of commands. Each command is a pair of lists of integers, like ([24, 2], [32, 1]), and means to replace the first as a sequence with the second, as many times as it occurs.

The program runs repeatedly until the accumulator does not change. Finally, the accumulator is output.

For example, with the input [5, 5, 5, 5] and the program ([5, 5], [3, 2, 1]), ([3], [5]), ([2, 1, 5], [5, 1, 2]), the list goes:

[5, 5, 5, 5]
[3, 2, 1, 3, 2, 1]
[5, 2, 1, 5, 2, 1]
[5, 5, 1, 2, 2, 1]
[3, 2, 1, 1, 2, 2, 1]
[5, 2, 1, 1, 2, 2, 1]


Your challenge is to interpret this language. You may take input and program in any reasonable format.

This is , shortest wins!

## Testcases

In the format of input, commands.

[5, 5, 5, 5], ([5, 5], [3, 2, 1]), ([3], [5]), ([2, 1, 5], [5, 1, 2]) -> [5, 2, 1, 1, 2, 2, 1]
[4], ([4], [4, 4]) -> Infinite loop
[2, 19, 13], ([13, 19], [2]) -> [2, 19, 13]
[39, 1, 23], ([1], [39, 23]), ([39, 39], [1, 1]), ([23, 23], [1]) -> [39, 23, 39, 23, 39, 23]


This language may be Turing-complete, and I have a +50 bounty for someone who proves it either way.

# How far from binary?

• Your description doesn't quite match your test cases. It should probably say that the absolute value of n-m is composed only of 1s and 0s. Since negative numbers have -.
– Wheat Wizard Mod
Jun 15, 2022 at 8:40
• @WheatWizard Why is it necessary? -101 is a signed binary. Jun 15, 2022 at 8:46
• -101 is not a binary string. It might be reasonable to interpret the intended way, but I certainly think it's more reasonable to interpret it another way. I don't see any harm in being explicit.
– Wheat Wizard Mod
Jun 15, 2022 at 8:48

# Parse this handy graph format

There's a great number of ways to represent directed graphs like the following:

Most representations are tailored towards being easy to work with, either for humans (like the picture above) or for computers (like an adjacency matrix representation). A middle ground I found useful in the past is this format:

        A -> B <-> C                A -> B -> C -> A           A -> C -> D; B <-> C <-> E


It is basically a condensed edge list, which is still relatively close to a graphical representation (good for humans) but not too hard to parse for a computer.

The goal in this challenge is to take a string representing a graph in this format as input and output a list of the graph's nodes and a list of the graph's edges.

This is , so try to use as few bytes as possible in the language of your choice.

### Input specification

• Each node has a unique name consisting of alphabetical letters, for example A, b, or Node. It is also fine if you only support upper or lower case names.
• Three types of arrows can appear: ->, <-, and <->.
• A chain is formed by a sequence starting with node and then alternating between arrows and nodes, for example A -> B <- C or also just A.
• A chain may be followed by another chain with ; as a separator in between.
• Between node names and the arrows and the semicolon can be any number of spaces (including zero).
• Self-loops are possible, i.e., A -> A describes an arrow from node A to itself.
• You may assume the input string is a valid encoding of a graph.

### Output specification

• The list of nodes can be returned or printed in any reasonable format and order, e.g., A, B, C, ["A", "B", "C"], A\nB\nC, ...
• Edges are represented as ordered tuples in any reasonable format, e.g., ("A", "B") or A B for the edge A -> B and ("D", "C") or D C for the edge C <- D.
• The list of directed edges can again be output in any reasonable format.

### Test cases

"A -> B <-> C"               : ["A", "B", "C"], [("A", "B"), ("B", "C"), ("C", "B")]
"A -> B -> C -> A"           : ["A", "B", "C"], [("A", "B"), ("B", "C"), ("C", "A")]
"A -> C -> D; B <-> C <-> E" : ["A", "B", "C", "D", "E"], [("A", "C"), ("C", "D"), ("B", "C"), ("C", "B"), ("C", "E"), ("E", "C")]
"AA<->BB"                    : ["AA", "BB"], [("AA", "BB"), ("BB", "AA")]
"A;B"                        : ["A", "B"], []
" "                          : [], []
"   A   <- B  ;  C  "        : ["A", "B", "C"], [("B", "A")]
"A -> A; B <- B"             : ["A", "B"], [("A", "A"), ("B", "B")]


#### Sandbox question:

Given that this is foremost a question, I'm tempted to drop the validity assumption and require answers to raise an error if the input does not follow the spec. What do you think, would that still be fun?

• Definitely don't require validity. That makes the challenge two quite different challenges, and is in no way necessary. Jun 27, 2022 at 1:00
• ^ probably a typo, but 100% you should allow users to assume validity. Don't require validity checking. Jun 30, 2022 at 2:06

# Flood fill by distance

• I suggest using a different character than O for obstacles, because it looks too much like 0. Maybe #? Jun 20, 2022 at 12:52
• In your third code block, the last two grids still use O intead of X in two places each. Jun 25, 2022 at 21:24

• There's a natural follow-up with the other possible addition operator, where the order of application is reversed, i.e. $$\\operatorname{add2}\overparen{\underparen a}\overparen{\underparen b} f=\left(\overparen{\underparen b} f\right)\circ\left(\overparen{\underparen a} f\right)\$$.
• Even though I've dabbled in similar contexts before, I would have been helped by a reminder to think of everything in terms of functions which act on functions. Jun 20, 2022 at 21:05
• It looks like the multiplication and exponentiation rules are part of the "Task", but if I understand right they're really an additional comment on add or a hint which could be useful for understanding / implementing / verifying behavior. Jun 20, 2022 at 21:14
• @thejonymyster add is binary, since it expects two curried arguments.
– att
Jun 20, 2022 at 22:14
• May I take input as $x_0,\dots,x_a$ without taking the integer $a$? Jun 23, 2022 at 11:45
• @alephalpha that should be allowed by default
– att
Jun 23, 2022 at 18:21
• I think the $\mathsf {formatting}$ might be clearer if you denoted "Church numeral of $n$" as something like $[n]$. Because at the moment, it's not entirely clear that $\mathsf {a^b}$ means $[a^b]$ and not $[a]^{[b]}$ (which doesn't make any sense) Jun 27, 2022 at 7:21
• @pxeger What do you think about $\overparen{\underparen n}$ / $\overparen{\underparen{a^b}}$ (or maybe only over)? I feel like braces add a bit too much clutter.
– att
Jun 27, 2022 at 19:36
• @att Sure, both work fine Jun 27, 2022 at 19:38
• @thejonymyster I think "where ∘ denotes function composition" should be sufficient (it's also defined as the multiplication rule)
– att
Jun 27, 2022 at 22:22
• Oh, i skimmed right over that. I guess my friend just can't read :P Jun 27, 2022 at 22:35

# Is this a squashed series? code-golfstringparsingnumberdecision-problem

Given a string of digits, determine whether it is the concatenation of at least two ascending consecutive integers. (in decimal, with no leading zeroes)

For example, the string 7891011 is valid, because it's the concatenation of the sequence [7, 8, 9, 10, 11].

However, the string 54 could only be formed by concatenating [5, 4] (which is not ascending), or [54] (which does not have at least two numbers in it), so it is not valid.

(This challenge is essentially asking "Is it a valid input to Decipher a squashed series")

You should output using two distinct values of your choice to represent "valid" and "not valid".

Take care with leading zeroes: for example, 809 is not valid, even though it could be decomposed into [8, 09], because 09 is not a valid decimal integer.

You may assume the input does not start with a 0, and has a length of at least 2. The input will also only contain digits (and not -, so you don't need to handle negative numbers).

This is , so the shortest code in bytes wins.

## Test cases

Valid

1234
7891011
293031323334
9991000


Invalid

54
66
28
3131
809


Valid numbers are given by A035333 in the OEIS.

# Meta

• Is this interesting enough? (It was just a byproduct of Decipher a squashed series)
• Is my handling of the 809 case good? Or should I allow either output for inputs like that?
• In Brachylog, this would be the exact same answer as your previous challenge, but I guess it’s mostly because of the declarative nature of the language. I don’t know if that’s interesting enough compared to the othe challenge with other language paradigms. Jun 28, 2022 at 13:58
• Fwiw, in 05AB1E it isn't the exact same answer, but it's a pretty trivial change. My initial answer was .œ.Δ¥P; and it would be .œʒ¥P}g without the 809 test case or .œʒ¥P}ïJQO with the 809 test case (both outputting 2/1 for truthy/falsey respectively). So the 8,09 test case definitely adds something interesting, although 05AB1E's "09"==9 being truthy makes it a bit more tricky than in most other languages I'd imagine. Jul 8, 2022 at 14:21

# Is it shuffled FizzBuzz?

## Decompress a Sparse Matrix (WIP)

The dual of this challenge.

Decompress a sparse matrix reversing the method here Compressed sparse row (CSR, CRS or Yale format).

There will be 4 inputs, either as separate variables or as a list of lists:

• V, a list of the nonzero elements of the matrix in row-major form. This is of length NNZ (the number of nonzero elements in the original matrix)
• NCOLS - the number of columns in the original matrix.
• IA - a list that yields the number of nonzero elements in each row in the following way: IA[0] = 0, IA[i] = IA[i - 1] + <number of nonzero elements in row i>. The number of nonzero elements in row i is IA[i + 1] - IA[i].
• JA - a list of the column indices of the elements in V, also of length NNZ. (zero-indexed)

Input will be a list of 3 lists and the number of columns in the original matrix, e.g. either

[
[5, 8, 3, 6],
[0, 0, 2, 3, 4],
[0, 1, 2, 1],
[4]
]


Or

V = [5, 8, 3, 6]
IA = [0, 0, 2, 3, 4]
JA = [0, 1, 2, 1]
NCOLS = 4


Output will be a decompressed matrix/list of lists:

[[0 0 0 0],
[5 8 0 0],
[0 0 3 0],
[0 6 0 0]]


If your language doesn't support actual data structures, input and output may be text.

### Process

1. Create a 'matrix' of row width NCOLS.
2. Populate the ith matrix row with N values from V if the corresponding array index (i + 1) of IA is non-zero, where N is the ith element of IA starting at the ith element of JA.
3. repeat until V is empty
i.e. above for the 0th matrix row IA[1] = 0, so this row has NCOLS=4 zeroes in it's first row. Then for matrix row 1, IA[2]=2 it takes 2 values from V starting at JA[1]=0. For matrix row 2, IA[3]=3 and IA[2]=2 so it takes the next (3 - 2 = 1) elements from V, starting at JA[2]=2. For matrix row 4 IA[4]=4 and IA[3]=3 so it takes the next (4 - 3 = 1) elements from V, starting at JA[3]=1.

### Test cases

Input 1:

[ 5, 8, 3, 6 ]
[ 0, 0, 2, 3, 4 ]
[ 0, 1, 2, 1 ]
4


Output 1:

[[0 0 0 0],
[5 8 0 0],
[0 0 3 0],
[0 6 0 0]]


Input 2

[ 10 20 30 40 50 60 70 80 ]
[  0  2  4  7  8 ]
[  0  1  1  3  2  3  4  5 ]
6


Output 2:

[[10 20 0 0 0 0],
[0 30 0 40 0 0],
[0 0 50 60 70 0],
[0 0 0 0 0 80]]


Input 3:

[ ]
[ 0 0 0 0 ]
[ ]
3


Output 3:

[[0 0 0],
[0 0 0],
[0 0 0]]


Input 4:

[ 1 1 1 1 1 1 1 1 1 ]
[ 0 3 6 9 ]
[ 0 1 2 0 1 2 0 1 2 ]
3


Output 4:

[[1 1 1],
[1 1 1],
[1 1 1]]


Input 5:

[ 5, -9, 0.3, -400 ]
[ 0, 0, 2, 3, 4 ]
[ 0, 1, 2, 1, ]
4


Output 5:

[[0 0 0 0],
[5 -9 0 0],
[0 0 0.3 0],
[0 -400 0 0]]


Assume inputs may contain any real number, you need not consider mathematical symbols or exponential representation (e.g. 5,000 will never be entered as 5e3). You will not need to handle inf, -inf, NaN or any other 'pseudo-numbers'. You may output a different representation of the number (5,000 may be output as 5e3 if you so choose).

### Scoring

This is a , fewest bytes wins.

• I'd suggest to at least briefly explain how the decompressing works in the post. The challenges should be self-contained as much as possible. Apr 22, 2021 at 23:55
• @bubbler, that's coming, but I need to figure out how to do that/explain it myself. I've left (WIP) on the question because of this. Apr 23, 2021 at 0:11
• @Pureferret I think it would be better to allow only nonzero integers instead of any real number. It'd be easier for most languages that way
– user
May 2, 2021 at 20:59
• @user I think it's more interesting seeing those languages work around those difficulties. Also the original challenge required them, so it I my makes sense this one does too. May 2, 2021 at 21:14
• @Pureferret I'm not sure many golfing languages support arbitrary precision floating point numbers. Would they be able to use strings, then? Edit: could you at least restrict it to rational numbers? Unlike Jon Skeet, most of us here don't know all the digits of pi :P
– user
May 2, 2021 at 21:17
• @user it needn't be arbitrary, just as long as it matches the test cases May 2, 2021 at 23:46
• @Bubbler I think the process is correct? Jun 29, 2022 at 16:17

## Round it up Nicely

When I work out, I often don't have a good plan for how many times to repeat an exercise, but in the interest of pushing myself I always keep going until I've done a "nice" number. Multiples of 5 are ideal, but multiples of 4 are acceptable too--unless they're 1 less than a multiple of 5, in which case I may as well do one more, or they're 1 more than a multiple of 5, in which case why didn't I already stop?

### The challenge

Given an integer $$\n\$$ and a descending, pairwise coprime list of integers $$\k_1, k_2, ..., k_m\$$, output the least integer $$\x \geq n\$$ which is a multiple of some $$\k_i\$$ but is not 1 more or less than any multiple of any $$\k_j\$$ with $$\j.

### Test cases

n    k[1]...k[m]                        result
1    [5, 4]                             5
15   [5, 4]                             15
12   [5, 4]                             12
16   [5, 4]                             20
7    [5, 4]                             8
996  [5, 4]                             1000
1    [11, 7]                            7
15   [11, 7]                            22
133  [11, 7]                            140
1    [5, 3, 2]                          3
6    [5, 3, 2]                          10
6    [5, 3]                             10
11   [5, 3, 2]                          12
1    [100, 49, 9]                       9


## Sandbox

• Would it be more interesting without the descending/coprime guarantees?
• Test cases are a WIP, but any additional suggestions?
• Better title?
• [How] should I note that the 1-above exclusion only matters if it would exclude the input itself? Should the task not be "rounding up" to make it more relevant?
• the "dynamic goal" thing made me think it was going to be a challenge about determining how much excersize youd be doing in a given section, the sequence thing seems way out of left field and the requirements to be a workout number arbitrary, even in relation to the lore Feb 3, 2022 at 4:43
• Could you please use words to describe the challenge? I do read quantifiers, but I suspect not all golfers do. Jun 30, 2022 at 6:25

# Draw the Progress Pride flag

• This is a really nice flag. It breaks one of the "golden rules of flag design" (no more than 3 colours) but that's the point. And harder to draw than it looks because you can't just draw a triangle for the brown and black. The spec is slightly inconsistent: the height calculated from the diagonal strip width is (340+170+170)*2 = 1360 which differs from the height calculated from the horizontal strip width 224 * 6 = 1344 so you might wat to fix that. Jun 24, 2022 at 21:04
• I think the spec is reasonably clear but I have a few suggestions: 1. delete the word "obviously" - too patronizing. BTW this is covered by one of the standard loopholes here on Meta - it's always good to reference them. 2. So the minimum size is 1100 x 672? I recommend you state it explicitly rather than saying "only half" . "Exactly" is a strong word (especially when 170/sqrt 2 is actually 120.20815 ) - I recommend an error of 1 pixel. Jun 24, 2022 at 21:12
• Thanks for the response I’ll fix this on Wednesday Jun 26, 2022 at 19:01

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

• ooh seems really fun Jul 1, 2022 at 18:13

# Implement Binary Exponentiation

• interestingly you can do the same thing with binary or peasant multiplication. actually any associative operation.
– qwr
Jun 26, 2022 at 21:16

# Is it an ordinal?

• An interesting variation could be an open-ended-function sequence with the task being to generate every ordinal. Although I don't know if there would be a better way to answer that than smushing this decision problem and a "generate every ragged list" algorithm. Jun 30, 2022 at 10:54
• @pxeger There's no way to generate every ordinal. There are uncountable ordinals, as well as countable but incomputable ordinals.
– Wheat Wizard Mod
Jul 7, 2022 at 7:23

# Draw the USA flag

• "then your score is half of your program's length" is generally not welcomed here.
– tsh
Jul 4, 2022 at 6:33

# Convert from Greeklish to modern Greek

• I like natural language challenges, however it seems a bit boring. I feel like we must have a few challenges already that are a substitution cypher with digraphs, and it probably isn't really doing anything new there.
– Wheat Wizard Mod
Jul 7, 2022 at 7:18
• @WheatWizard I understand that character substitution challenges do exist in the site. However, from my search of the sandbox, there isn't one for Greek, so it's somewhat original. Therefore, I am considering to post this. If this goes any well, I will also consider posting a harder natural language Greek challenge ;) Jul 7, 2022 at 8:08
• I just don't think that it being Greek actually makes the task any more interesting. Like it's neat, but the task is just a very simple substitution. If you have a harder challenge about Greek I'd say go with that one first.
– Wheat Wizard Mod
Jul 7, 2022 at 8:26
• @WheatWizard Since I made the effort to post and polish this a bit, I will post it. If it doesn't receive as much upvotes due to its unoriginality so be it. This site runs for many years and its hard to come up with something 100% original. Personally, I think its a solid challenge. Finally, I will also link to other related challenges, as I've seen quite recently on non-original challenges. Jul 7, 2022 at 8:41

# Every possible pairing

• Seems a little on the simple side I think. Might be a duplicate, but if it's not I think it's likely to score very well. :)
– Wheat Wizard Mod
Jul 8, 2022 at 20:05

# Infinite Fibonacci word code-golfsequencefibonaccistring

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 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 \$$.

Errors due to floating-point imprecision are not allowed.

This is , so the shortest code in bytes wins.

• Seems very similar to the infinite quote escaping sequence Jul 15, 2022 at 13:05
• It doesn't seem like it should be binary - 0 and 1 have no special meaning, they can be replaced by any symbol Jul 15, 2022 at 13:07
• @mousetail Yes, in fact the Fibonacci word can also be formed using a string rewriting rule like the quote sequence. In this case it's replacing 0 with 01, and 1 with 0. Jul 15, 2022 at 13:11
• This is a interesting challenge, however, of the 2 challenges I think the other one is slightly more interesting. Jul 15, 2022 at 13:13
• @mousetail Who's to say we can't have both? I think they're definitely not duplicates, because both have multiple different approaches, only one of which somewhat overlaps. Jul 15, 2022 at 13:14
• Fair enough, though I'd suggest to post it after the other challenge to acknowledge the inspiration Jul 15, 2022 at 13:24
• @mousetail It was not deliberately inspired by that challenge at all. (Maybe subliminally, because I had seen that challenge perviously?). But I learnt about the Fibonacci sequence independently while browsing Wikipedia. Jul 15, 2022 at 13:26
• I think you should specify if floating-point errors are allowed, since some approaches will probably use the golden ratio Jul 16, 2022 at 4:35
• @CommandMaster I've added a note about that, but AFAICT there aren't any direct methods to make the string using φ Jul 16, 2022 at 7:43
• Duplicate? Jul 16, 2022 at 8:57
• @pxeger the OEIS entry says "a(n) = floor((n+2)*r) - floor((n+1)*r) where r=phi/(1+2*phi) and phi is the Golden Ratio." Jul 16, 2022 at 9:22

# All Crossword Grids

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.

• Suggested tags: crossword, grid Jul 27, 2022 at 5:45
• I don't see any clever algorithm for grid generation (that doesn't mean that there isn't one), so the answers are most likely use the brute-force method of generating all grids and checking their crosswordness - why not make it decision-problem then? Jul 27, 2022 at 5:51
• @pajonk I've modified the question as per your suggestion, but that makes it very similar to a previously posed question, so I'm unsure about this. I think there are some meaningful shortcuts to make the generation easier. Jul 27, 2022 at 18:56
• if you see shortcuts that make generation easier than brute-force, then ignore my previous comment. Jul 28, 2022 at 9:36

# Add parentheses to Polish notation

• Suggested test-case with multi-digit numbers. Also, are the numbers guaranteed to be positive? Aug 4, 2022 at 12:50
• I think they should be limited to being positive. Aug 4, 2022 at 14:47
• I'd suggest removing the edge case that extra trash at the end needs removed (such as the + 1 2 3 test case). Of course, it's your challenge, just a suggestion. I prefer sticking to the actual problem, and not adding extra edge cases. Aug 4, 2022 at 17:23
• That was just a typo, sorry about that Aug 4, 2022 at 18:29

# Change The Quotations as if in Microsoft Word

META: Posted

• What to do with consecutive quotation marks? Or this won't ever be an input? Aug 7, 2022 at 15:17
• I've added a rule for that. Aug 8, 2022 at 5:58
• What will be the output for ''' and ''''? I other words, what is the precedence of the rules? Aug 8, 2022 at 6:02
• I've edited the rule I just added to accommodate these strings. Check it out. Aug 8, 2022 at 6:08
• How come “ makes a brief appearance in rule 5 and nowhere else? Aug 8, 2022 at 12:40
• Oops, didn't delete that. Aug 12, 2022 at 7:39