# 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 needs more feedback, but it's been ignored, you can ask for feedback in The Nineteenth Byte. It's not only allowed, but highly recommended!

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.

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# Best Rolling Ao5

• I'd suggest removing [rubiks-cube] and replace it with [array-manipulation and [floating-point]. I'd also recommend not requiring a trailing 0 if the output is only 1 decimal place (e.g. 28.3 for the last example) and mentioning that the sets are overlapping ("computing the ao5 for each overlapping set of consecutive five times") Apr 19 '21 at 22:26
• @cairdcoinheringaahing I want to keep the trailing zeros because that's how all times are displayed in official results. Does that make sense
– qwr
Apr 21 '21 at 3:24

# Is this number part of a Collatz prime sequence?

A fast step of the Collatz sequence is defined as

$$s_\mathrm{Collatz}:\mathbb{N}_\mathrm{odd}\to\mathbb{N},\quad n \mapsto \frac{3\cdot n+1}{2}.$$

Given an odd positive integer $$\n\in\mathbb{N}_\mathrm{odd}\$$, your task is to decide whether or not both $$\n\$$ and $$\s_\mathrm{Collatz}(n)\$$ are prime numbers.

Your program should output two distinct and unique values to represent truthiness and falseness, whereby falseness may also be represented by signalling an error.

Since $$\n+\frac12(n+1)=n+\lceil\frac n2\rceil\$$ for odd $$\n\$$, the sorted sequence of all numbers which result in truthiness in the above sense is equal to the tail of A158709.

## Test cases

-8 -> -        ; undefined behavior
1  -> false    ; (3*1 +1)/2 = 4 is not prime
3  -> true     ; (3*3 +1)/2 = 5 is prime
5  -> false    ; (3*5 +1)/2 = 8 is not prime
7  -> true     ; (3*7 +1)/2 = 11 is prime
11 -> true     ; (3*11+1)/2 = 17 is prime
15 -> false    ; 15 is not prime
91 -> false    ; (3*91+1)/2 = 137 is prime, yet 91 is not
97 -> false    ; (3*97+1)/2 = 146 is not prime

• What is the definition defining? Is $p$ a Collatz prime iff it's a prime and $\frac{3p+1}2$ is a prime? If $p$ a Collatz prime iff it's a prime and $\frac{2p-1}3$ is a prime? Or is a prime Collatz if either of those conditions hold? Sep 13 '19 at 10:56
• @PeterTaylor are they not the same thing? Sep 13 '19 at 11:09
• Alternative phrasing: which of $p_1$ and $p_2$ are you calling a Collatz prime? Sep 13 '19 at 11:11
• @PeterTaylor I mean $p_1$ Sep 13 '19 at 11:22
• So neither the input prime nor the Collatz prime need to be prime? Sep 17 '19 at 7:56
• "Input MAY be non-prime, in which case the output is always false (see 15)" -- did you specifically define this behavior or why is the above the case? Sep 17 '19 at 8:00
• @JonathanFrech I'm (personally) only interested in going from prime to prime, but I wanted to define the haviour for non-prime input. When I say 'may be non-prime' I mean, it should be able to handle it, it's an allowed/expected input but not one that gives a True output. Sep 17 '19 at 10:55
• To me it feels like an unnatural extra constraint. Sep 17 '19 at 12:54
• @JonathanFrech it's just defining how to behave with certain inputs. Sep 18 '19 at 9:12
• Citing Exceptional edge cases; such out-of-place definitions are generally frowned upon. Sep 18 '19 at 9:56
• @JonathanFrech I've changed the initial ask, and now it shouldn't be an exception Sep 18 '19 at 10:23
• Cf. A158709. Sep 18 '19 at 10:53
• @JonathanFrech Do you think this is postable? Apr 27 '21 at 1:17
• cf. Things to avoid when writing challenges: Prime numbers. Unless there's a mathematical way to avoid any of the existing golfed primality test methods, a task involving primality test is not very interesting. Apr 28 '21 at 6:09
• @Pureferret I would not post it -- unless you can think of an interesting golf opportunity. You could, however, improve the problem at hand: there are many questions one can ask about Collatz trajectories. And if you ask for something along the lines of "decide if the given number is a multiple of the length of its Collatz trajectory", you get a less arbitrary connection of concepts whilst preserving the topic of divisibility. Apr 28 '21 at 14:28

• How exactly are "printing" and "returning" distinguished? Are submissions required to be a function that also outputs to STDOUT in addition to returning a value from the function? Also, I would strongly advise against subjective criteria like having an error message related to tabs, unless they are purely for brownie points; point bonuses, especially ones that can't be judged objectively, are discouraged.
– hyper-neutrino Mod
Apr 17 '21 at 17:26
• Printing and returning can be considered identical to each other for the purposes of this challenge. Apr 17 '21 at 18:58
• I've edited this down to a stub now that it's been posted to save space Apr 28 '21 at 14:15

# Solve the Alien Probe puzzle code-golfarray-manipulation

• The description was clear to me, without watching either video. Doesn't seem like the wording needs much improvement. Apr 28 '21 at 13:54

# Drawing the Mathematics Stack Exchange logo (ASCII Logos 2)

The goal is to create the Mathematics Stack Exchange logo using ASCII characters.

It looks like this.

The exact output should look like this:

                   _
/=/ \=\
/=/       \=\
|             |
|\=\       /=/|
|   \=\ /=/   |
|      |      |
_    |      |      |    _
/=/ \=\  \=\   |   /=/  /=/ \=\
/=/       \=\  \=\|/=/  /=/       \=\
|             |    |    |             |
|\=\       /=/|         |\=\       /=/|
|   \=\ /=/   |         |   \=\ /=/   |
|      |      |         |      |      |
|      |      |         |      |      |
\=\   |   /=/           \=\   |   /=/
\=\|/=/                 \=\|/=/
/=/   |   \=\           /=/   |   \=\
|             |         |             |
|\=\       /=/|         |\=\       /=/|
|   \=\ /=/   |         |   \=\ /=/   |
|      |      |         |      |      |
|      |      |    _    |      |      |
\=\   |   /=/  /=/ \=\  \=\   |   /=/
\=\|/=/  /=/       \=\  \=\|/=/
|    |             |    |
|\=\       /=/|
|   \=\ /=/   |
|      |      |
|      |      |
\=\   |   /=/
\=\|/=/
|


You must make sure the cubes should be symmetrical just like the original logo, and must make space to create a 6-point star in the middle. Yes, the output looks messed up, but it's all I can do to really make a shape.

Remember, 6 boxes aligned as a hexagon.

Can you draw it with the least bytes possible?

Tags: ,

Any suggestions?

If this question reaches a score of 4, it will be posted on 12:00 PM UTC, 1 month after Stack Overflow's.

# KoTH - JS WarBots

Based on King of the Hill: Robot Battle

## Rules and Instructions

Program a bot as an object in JavaScript. The functions that can be called are:

• left(name) Moves left 1 unit (x position -1)
• right(name) Moves right 1 unit (x position +1)
• up(name) Moves up 1 unit (y position -1)
• down(name) Moves down 1 unit (y position +1)
• forward(name) Moves forward 1 unit (z position -1)
• backward(name) Moves backward 1 unit (z position +1)
• mine(name) Places a mine at current position (bots can be blown up by their own mines, with a 1 tick delay before priming)
• scan(name) Scans for mines and players in adjacent cells (cells a bot can move to). Returns an array [left, right, up, down, forward, backward]. Each element can be 0 (nothing there) 1 (mine) 2 (other bot).
• pass(name) Do nothing

name is the name of the bot. Any bot whose action's name is not the name of the bot will be disqualified (if your bot is called "Foo" you must have pass("Foo") and not pass("foo") or pass("Bar"))

The 3D arena is a 1000x1000x1000 cube, centered at (0,0,0). Each turn of a game, every bot must select one of the above actions to perform. Every 10 turns (subject to change) minesweeping will occur, removing 50% of the existing mines to reduce camping.

A bot is eliminated from a game if:

• It is in the same position as a mine.
• It exits the game area.
• It collides with another bot (both bots are eliminated).
• The cell that it occupies does not have integer coordinates ((0,0,0) is valid, (0.5,0,0) is not)

## Scoring

After 1000 turns, if a bot is not eliminated, it receives Math.floor(1000/bots) points, where bots is the number of bots left. If a bot eliminates another bot by mining it, it receives 100 points. If there are no bots left after 1000 turns, nobody gets any points.

Here are examples of bots (These will be playing too!):

### RandomBot

var RandomBot = { // Same name as the name property
name: "RandomBot",

x: Math.floor(Math.random() * 1000 - 500), // If unspecified, defaults to 0.
y: Math.floor(Math.random() * 1000 - 500), // If unspecified, defaults to 0.
z: Math.floor(Math.random() * 1000 - 500), // If unspecified, defaults to 0.

turn: () => {
var action = Math.ceil(Math.random() * 9)
if (action == 1) { left("RandomBot") }
else if (action == 2) { right("RandomBot") }
else if (action == 3) { up("RandomBot") }
else if (action == 4) { down("RandomBot") }
else if (action == 5) { forward("RandomBot") }
else if (action == 6) { backward("RandomBot") }
else if (action == 7) { mine("RandomBot") }
else if (action == 8) { scan("RandomBot") }
else { pass("RandomBot") }
}
}


May the best bot win!

### The challenge will be posted later when it receives sufficient votes and the controller is developed. If there are any questions regarding this challenge, please comment about it.

• Is there anything preventing a bot from placing six mines around itself, then never moving? Apr 30 '21 at 16:03
• @RedwolfPrograms Do you have any suggestions on preventing that? Apr 30 '21 at 16:33
• @RedwolfPrograms I've created another rule regarding camping. Apr 30 '21 at 16:44
• I think the problem is less camping itself, and more just that I don't think there's very much strategy possible. The current restriction is trivially beatable by just enclosing yourself in a 1x1x2 space and moving back and forth. Apr 30 '21 at 17:41
• @RedwolfPrograms Maybe there should be a limit on how many mines you can place? Apr 30 '21 at 17:57
• That could lead to some interesting gameplay, but might actually make the camping problrm worse because it takes very few mines to do. I'd recommend writing a few rough bots on a sheet of paper, and running some games in your head, then seeing what makes it fun and what could use some improvement. I think there needs to be more room to do interesting things; currently there's not really much strategy beyond "don't run into mines". Apr 30 '21 at 18:20
• @RedwolfPrograms I came up with an idea regarding the issue that you brought up. There could be a minesweeper that runs every 10 or so turns where 50% of mines are removed. Apr 30 '21 at 19:15
• I think the idea behind that is good, but it has the same problem of being easily fixable by campers, and also removing plenty of mines set up by other players. Apr 30 '21 at 20:39
• @RedwolfPrograms I will consider new methods for the issues in the challenge. Apr 30 '21 at 20:43
• Should I move this to chat? Apr 30 '21 at 20:48
• Apr 30 '21 at 20:51
• Just wondering, why use functions rather than return values? e.g. having the bot return "left" rather than call left("name"). Also, right now, this just seems like a 3D version of Robot Battle. The three-dimensionality might actually be a bad thing, though, since it makes it harder to trap bots using mines. Like Redwolf, I also encourage you to think about the rules and the strategy of the game to try to allow for more strategy, and to differentiate it from the challenge it's based off of. May 4 '21 at 2:37
• Also, the camping can be reduced to scanning, going into a corner, placing three mines around you, and waiting. May 4 '21 at 5:54

# xkcd 2385

• Now that this has been posted, it should probably be edited down and deleted. May 3 '21 at 1:38

# How many Faro Shuffles for a cycle?code-golfarray-manipulationcard-games

• @Pureferret it has been! May 3 '21 at 13:27

# Produce a range

Your task is to take a list of integers and find inputs to a Python range call to produce that list. That is, output three values (start, stop, step) so that range(start, stop, step) equals the given list.

You can assume that this is possible, which means that consecutive numbers in the list all have the same nonzero difference. Be careful that your code works for negative step sizes, as well as for empty or singleton inputs.

How range works

Python's built-in range produces a list* of equally-spaced numbers. Called as range(start, stop, step), it counts from the start value in increments of step like

[start, start + step, start + 2 * step, ...]


This list continues as long as the value is below stop given positive step, or above stop given negative step. If the start value already fails this test, an empty list is produced. Note that the stop value itself is never included in the list, giving a half-open interval.

range(0, 5, 1)   = [0, 1, 2, 3, 4]
range(0, -5, -1) = [0, -1, -2, -3, -4]
range(0, 2, -1)  = []
range(0, -2, 1)  = []
range(3, 4, 10)  = [3, 7]
range(3, 4, 11)  = [3, 7]
range(3, 4, 12)  = [3, 7, 11]
range(1, -2, 0)  = [1]


*In Python 3, it actually makes a range object, but we'll ignore that distinction.

Test cases

Note that there can be multiple valid inputs. Different stop values can cut off the result at the same point when the step is not ±1. A singleton or empty list can be produced in many ways.

TODO

• Is this return {a[0], a[-1]+sign(a[1]-a[0]), a[1]-a[0]}? May 7 '20 at 15:43
• @mypronounismonicareinstate I think that works for inputs with 2+ elements, though the empty list and singleton list also need to be handled. Is this too simple for a challenge?
– xnor
May 7 '20 at 19:32
• (I just noticed this might work in languages with modular indexing) This is probably not too simple, and I like the idea, but it seems like most of the complexity here comes from these special cases. May 8 '20 at 2:46
• Both Python 2 and Python 3 disagree with step=0 in range. range(1, -2, 0) would raise ValueError instead. Is this intend behavior in this challenge? Also, some languages (Matlab) would support range with floating point values, which some floating point errors may introduced. If you are not aiming to work on floating point errors, maybe add a integer tag.
– tsh
May 11 '21 at 2:24

# Are You My Mother? (very WIP)

(coincidentally, thought up around mother's day)

Oh no! All the newly-hatched ducklings have been mixed together, and they all look the same! The ducklings want to reunite with their own mother. But the mothers are also selfish and want as many ducklings as possible to go home with them. Since all the ducks look the same, the only way to tell who your mother is is by how she acts.

Your task is to write two bot algorithms: one for the mother duck and another for the ducklings.

# The game

There are 5 ducklings for each mother duck

All submissions compete at the same time

All of the ducklings line up in a 1-dimensional array in the pond, as do the mother ducks. They do not move around.

Each turn, each duck (either duckling or mother duck) can do one of the following actions:

• Do nothing
• Quack
• Flutter its wings
• Splash
• Spin around
• some other action

Each duckling will see the actions of each mother duck on each turn

After 20 turns, each duckling guesses which half of the mother duck array contains its mother (the upper half will get the mother duck in the middle when there are an odd number of mothers) and the process continues until each duckling has narrowed down to a single mother duck.

## Duck(ling) limitations

Ducklings are young and have poor memory. They cannot remember how long they have been lined up and can only remember the last thing each mother duck did when deciding what action to take. The only working memory available to ducklings is a single integer between 0 and 15, inclusive.

Mother ducks have a bit more memory and can remember five integers between 0 and 15, inclusive.

## Scoring

Score 1 point for each of your ducklings that went home with its mother. Score 1 point for each duckling (regardless of whose it is) that went home with your mother duck.

• Controller/submission language? (suggesting ecmascript if you haven't already written one) May 7 '21 at 23:19
• @Wezl yeah, probably Javascript May 10 '21 at 15:53
• The narrowing logic might be a bit unfair if, say, a duckling is unsure about two ducks, but they are in different halves, while another duckling is unsure about two ducks that are next to each other, so has much more time to decide. Plus, I think, 4 bits are very little storage; I'd allow at least 16 or 32 bits, which is a bit more but still limiting.
– FZs
May 18 '21 at 16:05
• @FZs I've considered the alternative of letting each duckling have 1-on-1 time with each mother duck, after which they can decide whether to go home with her or not. But they do not get a second chance. Not sure how to handle orphan ducklings there though. May 18 '21 at 16:19
• And what if the ducklings had to return a mother index on the choice-time? Or if the ducklings had to return an array of mother indices, and on the subsequent turns, it'd only receive info about the ones it chose previously; finally, after n turns, they have to decide? These are just ideas, so you don't have to accept them as they are...
– FZs
May 18 '21 at 17:38

# CGCC sings a song together

• Does "languages can only be used once" mean that each user can only use each language once, or each language can only be used at most one time in the entire challenge? i.e. if Alice uses Language A, can Bob use Language A in his answer? May 10 '21 at 3:22
• @AndrewLi Each language may only be used on a single answer, regardless of who posts that answer May 10 '21 at 15:23
• That makes sense, although 74 different languages sounds like a lot, so maybe it would be hard to find "good" languages near the end? I guess that's kind of the point though. I haven't really done any of these challenges so I don't know whether it would get hard to find a language near the end. May 10 '21 at 16:14

# Modify to Increment: Javascript Edition (WIP)

Your task is to insert bytes/characters into the previous answer such that it outputs the next number in sequence, spelled out in English, as its return value. The first answer must output one.

## Coding restrictions

Your answer's code must be atomically irreducible, meaning that if it is possible to remove some subset of lexical tokens from the code and have it produce the same output, then it is an invalid answer. Note that this is a distinctly different concept from removing characters from the code, as it treats identifiers, string literals, numbers, and operators as indivisible entities. For the purposes of this challenge, a comment is considered a lexical token, so commenting out parts of the previous answer is not allowed by virtue of this restriction.

Some tokens are not subject to this restriction:

• The declaration keywords let, var, and const
• Semicolons

Note that removing an operator between two tokens does not merge the tokens together into one token, so removing the + from 1+1 would result in 1 1 rather than 11

SANDBOX NOTE: I'm debating whether this should be tightened up to character-wise irreducibility, but I'm thinking that may be too restrictive and be too difficult to chain. On the other hand, quoting and escaping into an ever-growing .substring call seems to be a pretty easily-exploited loophole here. Perhaps a simple bandaid solution would be to ban more than 3 consecutive backslashes. Though perhaps this isn't a problem at all because answers will be trying to make it as hard as possible to chain.

## Multi-digit spelling

For numbers above 20, the result should be spelled with multiple words. You may use spaces, hyphens, or underscores to separate words and this does not need to be consistent. (e.g. twenty three can be followed by twenty-four, and one hundred-thirty four is valid even though the spelling looks weird)

Should this challenge reach more than 100 answers, the expected format should be like one hundred thirty six rather than a hundred thirty six. You may optionally insert and between hundred and the next word.

## Example

_=>'one'


_=>'twone'.substring(0, 3)


_=>'threewone'.substring(0, 3+2)


_=>'thfoureewone'.substring(02, 3+2+1)


_=>'thfoureewone'.replace('our', 'iv').substring(02, 3+2+1)


## Rules and Scoring

• You may not comment out part or all of the previous answer.
• This includes pseudo-commenting such as enclosing code in strings, using the comma operator to no-op parts of the code, or wrapping blocks in if(0)
• The case of the output does not matter (e.g. OnE is just as valid as oNE)
• No third-party libraries or vendor-specific features are allowed. The only features allowed are those found in the ECMAScript standard library as of May 14, 2021.

The first answer to go 7 days (i.e. 168 hours) without a successor is the winner.

• Looks like an interesting challenge idea! I think more formally defining what "pseudo-commenting" entails would help. For example, would [a, b][0] be invalid? What about 0 ? a : b? Also, I think you need to formalize what answers need to output; there are a couple different ways to spell english words. For example, is 147 "a hundred forty seven", "one hundred forty-seven", "one hundred and forty-seven"? etc.
– hyper-neutrino Mod
May 13 '21 at 19:09
• I think an "irreducible" requirement may help this question. How should multi-digit numbers be spelled? May 14 '21 at 11:54
• @Razetime Could you elaborate on irreducibility? The only thing that comes to mind is to require that the solution will not output the correct number spelled out if some subset of characters are removed May 14 '21 at 15:17
• yeah that is pretty much the exact definition. May 14 '21 at 15:19
• I think strict irreducibility might make it too hard to chain, though it does trivially ban comments and pseudo-comments. May 14 '21 at 15:28
• Try x=>'Xforty-two'.slice((function(){/* w h a t e v e r p r e v i o u s a n s w e r w i t h s p a c e s i n s t e r e d i n t o e v e r y 2 c h a r a c t e r s */}+'').length===155)
– tsh
May 17 '21 at 7:30
• @tsh maybe irreducibility isn't the right solution. Maybe the limitation needs to be a maximum number of characters added. May 17 '21 at 14:38
• An alternative would be to make adding to the solution also be atomic, so 'one' cannot become 'twone' May 17 '21 at 14:47

# Just Enough Ones

• Looks good to me. Not a big fan of OEIS questions in general, but this is one of the better ones. May 12 '21 at 19:09

# An approximation for factorials of reals

One approximation for factorial function of reals is the following function:

$$\ F_0(x) = \lfloor x \rfloor ! { \lceil x \rceil } ^ { x - \lfloor x \rfloor } \$$

The function is less inaccurate for higher values of $$\ x \$$, meaning that you can get better approximations using the following recursive definition:

$$\ F_{n+1}(x-1)=\frac1x{F_n(x)} \$$

Examples:

$$\ F_0(\frac72)=3!\times4^{1/2}=12 \$$

$$\ F_1(\frac52)=12/\frac72=\frac{24}7 \$$

$$\ F_2(\frac32)=\frac{24}7/\frac52=\frac{48}{35} \$$

$$\ F_3(\frac12)=\frac{48}{35}/\frac32=\frac{32}{35} \$$

$$\ F_4(-\frac12)=\frac{32}{35}/\frac12=\frac{64}{35} \$$

Given non-negative integer $$\n\$$ and real (well, floating-point) $$\x>-n\$$, please calculate $$\ F_n(x) \$$.

This is , so the shortest program or function that breaks no standard loopholes wins!

Bonus brownie points for using your code to approximate $$\ \lim_{n\to\infty}F_n(-\frac12) \$$:

$$\ F_1(-\frac12)=2 \$$
$$\ F_2(-\frac12)\approx1.89 \$$
$$\ F_3(-\frac12)\approx1.85 \$$
$$\ F_4(-\frac12)\approx1.83 \$$
$$\ F_5(-\frac12)\approx1.82 \$$
$$\ F_6(-\frac12)\approx1.81 \$$
$$\ F_7(-\frac12)\approx1.80 \$$
$$\ F_{10}(-\frac12)\approx1.79 \$$
$$\ F_{18}(-\frac12)\approx1.78 \$$
$$\ F_{88}(-\frac12)\approx1.77 \$$

Posted

• Maybe consider order testcases simply from -4 to 16? (Without sorted on their output length) Also, maybe add some larger testcases (no need to list all possible solutions if there are too many. maybe you can show one possible solution, and answers need to having same length output)
– tsh
May 14 '21 at 4:01
• @tsh I can add slightly bigger test cases, but there are no known efficient algorithms to calculate it, so I'm bounded by about 100 May 14 '21 at 4:14
• Okay, after larger testcases added, it is not equal to oeis.org/A056792 now. :)
– tsh
May 14 '21 at 5:30
• I believe that one can construct the answer without brute force search. So don't worry about it bound. It is up to you to decide if brute force search is allowed: If allowed, you may say "your program should be able to calculate answers for |n| < 100, and your algorithm should apply to any size n in theory"; If not, you could say "your program should be able to compute up to $\pm 10^8$ in reasonable time (not time out on tio for example)" in the question.
– tsh
May 14 '21 at 5:45
• @tsh from wikipedia: "the determination of a minimal addition-subtraction chain is a difficult problem for which no efficient algorithms are currently known" May 14 '21 at 5:47
• If i understand that statement correctly, it means an efficient (or polynomial) algorithms in $O(P(\log_2 n))$ is not exist. But A solution works under, say, $O(n)$ or maybe $O(n^2)$ is still possible.
– tsh
May 14 '21 at 5:58
• Maybe, but I'm also not aware of any pseudopolynomial algorithm which solves it May 14 '21 at 6:01

# Convert version string to pack_format code-golf

Posted

• @Arnauld thanks, fixed May 16 '21 at 16:52

### Telephone Cipher Encoder

The telephone cipher is a relatively basic cipher originating from the book The Terrible Two. The cipher is explained here as follows:

Does this keypad (below) look familiar? It does? Good. You’ve seen a phone before.

Now, in the telephone cipher, there are two numbers for each letter. The first digit corresponds to the number on a telephone, while the second digit corresponds to the position on the key.

For example:

21 = A

Why? Because A is located on the number 2 on the keypad and A is in the first position of that particular key.

22 = B

B is located on the 2 key and is in the second position of that key.

53 = L

L is located on the 5 key and is in the third position on that key.

Given an input string s, the program should output the string encoded with the telephone cipher.

s may contain single spaces between words, but will not have leading or trailing whitespace and will use only lowercase letters a-z. s will always have a length greater than or equal to 1.

The output should contain no whitespace and be properly encoded with the telephone cipher as described above.

As an example, the following input:

hello world


Should result in:

42325353639163735331


All usual loopholes are disallowed. This is code golf so shortest answer in bytes wins. May the odds be ever in your favor!

• What about the evens? :P May 18 '21 at 21:15
• Back to the days mobile didn't have a touch screen, I typed 4433555 555666 instead of 4232535363 for hello...
– tsh
May 19 '21 at 2:58

# Memory KoTH

Memory is a game where a bunch of pairs of identical cards are laid upside down, and you try to find pairs while only looking at two at a time.

In this KoTH, the way it will work is:

The game will be played on a 4096-item array, and the "cards" will be integers 0-2047.

Each bot takes its turn in order. It has access to the results of previous moves (Up to its previous turn), but their only storage is a single integer.

# Spec

The controller will be written in Javascript.

The bot has a move function, which must return two integers: The positions of both its guesses, in the form [g1, g2], where both are integers between 0 and 4095, and must not be gone already (see below).

The most recent move of every bot, including itself, in the form of an array of [g1,g2,r1,r2], where r1 and r2 are the first and second values revealed. The first item of this will be your bot's most recent guess, and the rest will be the other bots. This will be the global variable prev, and is readonly.

A picture of the entire grid, as a 4096-item array, left to right and top to bottom, where 0 means gone and 1 means still there. This will be the global variable grid, and is readonly.

An array of values that are gone. This will be the global variable gone, and is readonly.

A single ArrayBuffer(50), a 50-bit set of raw binary data. See the docs for help on how to access this. This will be the property this.storage, and can be used to store data.

Writing to globals is banned.

# Game

The bots will take their turn in a predetermined randomised order.

If a bot's moves are two tiles with the same value, those tiles are removed from the game area, and that bot gets a point.

The game ends when all tiles are gone, and the bot with the most points wins. In case of a tie, the bot that is last in the randomised order wins.

Bots should be a Javascript object like:

{
name: "A bot",
move(){
// insert code here
}
}


# Meta

Should I change storage limit or grid size?

• Shouldn't the bot be able to see the values of gone items? May 15 '21 at 9:03
• @CommandMaster True, will add. May 15 '21 at 21:02
• This doesn't really matter too much but if it were up to me, personally, I would change the storage limit from $[1,2^{50}]$ to $[0,2^{50}-1]$ so it's a bitstring of length 50
– hyper-neutrino Mod
May 18 '21 at 6:10
• @hyper-neutrino Oh yes, that's what I intended. May 18 '21 at 6:11
• What if two bots tie? May 18 '21 at 8:18
• @StackMeter The one that is last in the randomised order wins. I'll add that. May 18 '21 at 8:41
• Wouldn't it be easier to use a Uint8Array rather than a Bigint? Purely for ease of use. May 20 '21 at 12:51
• Also need to make it clear that writing to globals is banned, since that's a legal play right now May 20 '21 at 12:52
• @EnderShadow8 Yes, writing to globals is banned. May 20 '21 at 20:07
• @EnderShadow8 How would I format this Uint8Array? Like how many items would it need to be restricted to? May 20 '21 at 20:07
• Up to you. It's just a more convenient method of storing data that's a certain size. May 20 '21 at 23:32
• @EnderShadow8 Actually, I think a BigInt would be better for this challenge, as remembering a single tile is 23 bits, which would be confusing to fit into a Uint8Array. May 21 '21 at 4:22
• Just make it a plain ArrayBuffer and DataView. That's easier. I don't like using bit operations to extract data from integers. May 21 '21 at 4:42
• @EnderShadow8 Ok. May 21 '21 at 4:43
• Are you considering giving the bot the result of its first guess before asking for its second? That would introduce a new layer to the strategy. Eg. explore on the first move and defend or attack on the second May 21 '21 at 5:04

# Calculate $$\ \lfloor n \log_2(n) \rfloor \$$, exactly

Given an integer $$\ 2 \le n \$$, you need to calculate $$\ \lfloor n \log_2(n) \rfloor \$$, assuming all integers in your language are unbounded.

However, you may not ignore floating-point errors - for example, in python lambda n:int(n*math.log2(n)) is an invalid solution, because for example for n=10**15, int(n*math.log2(n)) is 49828921423310432, while the actual answer is 49828921423310435.

## Test cases

2 -> 2
3 -> 4
4 -> 8
5 -> 11
6 -> 15
7 -> 19
8 -> 24
9 -> 28
10 -> 33
100 -> 664
1000 -> 9965
10000 -> 132877


10 brownie points for beating my 4 byte 05AB1E answer.

This is code golf, so the shortest answer wins. Good luck!

# Symmetrical Triangles, posted

## Meta Questions

• Dupe?
• More tags?
• Should I allow/disallow more output formats?
• Is "An equilateral triangle array" clear, or is there a way I can clarify it?
• Especially relevant test cases?
• Is there an easy way to take up less vertical space and still have a good amount of test cases?
• This might not actually be more clear, but I think you can describe it as "output w lists of sizes [1, 2, ..., w] of 1/0s such that the total number of 1s is equal to n and each sublist is a palindrome".
– hyper-neutrino Mod
May 17 '21 at 20:51
• May 19 '21 at 15:29
• @hyper-neutrino it doesn't have to have each sublist a palindrome to be symmetrical May 19 '21 at 15:30
• When I first read this, I thought that it only took one input n, and had to output a n-sized triangle with n 1s. Now I realise that the size is a different input, but I think it could be more interesting if n == w? May 19 '21 at 15:31
• @pxeger I don't think that makes it more interesting, especially since it removes the point of the challenge (arranging the 1s), by allowing them to be always placed at the bottom of the triangle. May 19 '21 at 15:34
• @Wzl ah, I didn't think of that May 19 '21 at 15:43

# Backromymiser code-golfstringsubsequence

## Background

A backronym is an acronym that was formed from an existing word. For example, spam is actually named after the canned meat product as used in the Monty Python sketch, but can be interpreted as "stupid pointless annoying mail".

They can also be constructed using a more facetiously, such as "What Horse shYte" (that chat conversation was the inspiration for this challenge)

## Challenge

Given a sentence a and a word b, capitalise the correct letters of a such that they spell out b.

You may assume a will always consist only of lowercase ASCII letters and space, and b will always consist only of uppercase ASCII. Alternatively, you may assume b will always be lowercase, but this must be consistent.

You do not need to handle empty inputs or inputs that have no possible backronymisation.

You should always move left-to-right and capitalise the first occurence of each letter.

## Example

a = "im never gonna give you up", b = "VIP"

• Working through the letters of VIP:
• v: find the first instance of v in im never gonna give you up and upper-case it -> im neVer gonna give you up
• i: find and upper-case the next instance of i (after the already found v) -> im neVer gonna gIve you up
• p: do the same with p -> im neVer gonna gIve you uP

## Test cases

a                             b        output
=====================================================================
"im never gonna give you up"  "VIP"    "im neVer gonna gIve you uP"
"dbdacbec"                    "ABC"    dbdAcBeC
"x"                           "X"      "X"
"xxxx"                        "X"      "Xxxx"
"what horse shyte"            "WHY"    "WHat horse shYte"
"facdbbbd"                    "ABC"    (impossible; does not need to be handled)


# Meta

• Is this a duplicate? (related, related)
• Is this clear enough?
• Any other feedback?
• I quite like this challenge, but why are there four possible outputs for xxxx, X? Was it not specified that the first occurrence should be capitalized and only that one?
– user100690
May 27 '21 at 19:31
• I'll change it so that it's always the first option. May 28 '21 at 7:35

# Prime Factorization - but on the exponents too

• There seems to be a stray double-quote here: "2^(2^2^2)*(3^2). Should it be removed, or should there be a matching one at the end? May 28 '21 at 8:57
• There shouldn't be in the output - it was just to show the string format May 28 '21 at 8:58
• I've edited this down to a stub now that it's been posted to save space Jun 1 '21 at 23:12
• Can answers use vertical tabs instead of space padding? Also, I'd suggest saying that "$n$ will be a positive integer", as "integer" could be zero/negative May 31 '21 at 15:22
• edited: hopefully makes sense May 31 '21 at 15:37
• We usually allow a wide range of I/O methods. It is recommended to rethink your I/O restriction (mainly because it will get downvotes if people think the I/O restriction is unnecessary). Also, is it allowed to print trailing spaces after the backslashes on each line, or a trailing newline after the last line? (I guess yes to the latter from your code, but it's always better to be explicit) Jun 1 '21 at 4:34
• Strictly speaking, that line you are drawing actually has a length of sqrt(32). I think you should make it clear that the length refers to the number of non-whitespace characters. Also, "use a constant in your code" seems to be frowned upon as a method of input.
– user100690
Jun 1 '21 at 15:57
• how is the length $\sqrt{32}$??? Jun 2 '21 at 13:53
• Good challenge as a new user.
– qwr
Jun 2 '21 at 14:14
• The challenge is easy enough that it should not be necessary for answers to explain themselves. Answerers will do this voluntarily if they think it is necessary.
– qwr
Jun 2 '21 at 14:16
• @MaanasB pythagorean theorem. sqrt(4^2 + 4^2) = sqrt(32)
– user100690
Jun 4 '21 at 17:36

# Combinatorial Pipes

You're a plumber working on a house, and there's some pipes that must be connected at odd angles. You have 8°, 11.25°, 22.5°, 45°, and 90° fittings at your disposal, and you want to use as few as possible to match the angle as closely as possible.

# Goal

• Match the desired angle as closely as possible, with as few fittings as possible. It can be over or under the desired angle.
• Accuracy is more important than the number of fittings
• In the case of two different sets of fittings with the same resulting angle, whichever has the fewest number of fittings should be selected.
• If the two sets use different fittings, match the same angle, and have the same number of fittings, either may be chosen.

# Input

Your input is a random integer between (non-inclusive) 0 and 180, which represents the desired angle.

# Output

Your output should be an array where [0]-># of 8° fittings, [1]-># of 11.25° fittings, etc. If your language does not support arrays, you may output a comma separated list, where the first value represents the number of 8° fittings, and so on and so forth.

Test Cases

90° ->[0,0,0,0,1]
24°-> [3,0,0,0,0] ([0,0,1,0,0] uses less fittings, but is less accurate and therefore incorrect)
140°->[2,1,2,0,1]
140°->"2,1,2,0,1" acceptable if language does not support arrays


# Scoring

Lowest byte count for each language wins a high five from me if we ever bump into each other (and the challenge).

## Sandbox Questions

Howdy! I feel like this could be an interesting golf, but I'm unsure if the language is clear and concise enough to get the idea across.

• Might be interesting to make it more general, give a list of possible pipe fittings as an argument? Jun 16 '21 at 9:12

# Decode USB packets code-golfbinarycoding-theoryencoding

Posted

• Does this not basically boil down to base-conversion? Jun 9 '21 at 12:59
• @pxeger Base conversion will not work. For one base conversion generally ignores leading zeros, while 00010 /= 10, so its not a bijection. But even if you ignore that it's nowhere near monotonic. 11 > 100 but f(11) = 10 < 11 = f(100).
– Wheat Wizard Mod
Jun 9 '21 at 13:25

# Remove All Comments From Smalltalk for Code Golf

## Tags?

• May string contains \" as escaped characters?
– tsh
May 31 '21 at 8:05
• I might suggest changing  to a different character, simply because it's hard to use in markdown May 31 '21 at 8:43
• @tsh no ;) May 31 '21 at 16:20
• Suggest testcases with multiple groups of strings, multiple groups of comments, and their combination: "a"b"c", 'a'b'c', a'"'b'"'c, a"'"b"'"c
– tsh
Jun 1 '21 at 6:19
• I'm not sure if this'd be very interesting, since it's just a matter of replacing /"[^"]"/ if I'm correct.
– user
Jun 10 '21 at 1:03
• @user I think there's a misunderstanding. The program must also not remove comments in strings, such as 'a"b"c' is not changed Jun 10 '21 at 1:23

# Determine Centrosymmetric String

Let's define a centrosymmetric string as follows:

• First, add spaces to the end of each line to make the input a rectangle $$\ A_{m×n} \$$.
• The input is "centrosymmetric" string if and only if you get the original rectangle if you rotate the rectangle 180°. That is, it has 2-fold rotational symmetry, so $$\ A_{i,j}=A_{m+1-i,n+1-j} \$$ holds for all $$\ A_{1\dots m, 1\dots n} \$$.

## Input

Input a non-empty string. You may assume it:

• does not contain leading / trailing new lines;
• does not contain trailing spaces on any lines;
• only contains new line, space, and lowercase a-z.

You may choose to handle any of CR, LF, or CR-LF as the new line character in your program.

Input may be in any reasonable format, including but not limited to:

• A built-in string type;
• A NULL-terminated character array;
• An array of integer code-points;

Note that you are not allowed to take the string padded already as it trivialises the challenge.

## Output

Determine if the given input is a centrosymmetric string (as defined in this post), outputting two distinct values, or truthy vs. falsey values (they can be swapped relative to their normal meaning).

## Test cases

### Truthy

a

aba

a
b
a

ab
ba

abc
cba

abc
ded
cba

a a

a

a

a

a

a c
b
c a

a

b
b

a

zzzzz
z
z
z
zzzzz

n  n  oo   oo  n  n
nn n o  o o  o nn n
n nn o  o o  o n nn
n  n  oo   oo  n  n


### Falsy

ab

a
a
b

a
b
a

ab
ab

aa
bb

   a
a a
aaaaa
a     a

• I think a worked-through example would be a good idea May 31 '21 at 8:29
• What is the meaning of the 2 in A_{m×n}2? May 31 '21 at 8:37
• Related May 31 '21 at 8:39
• When you say "square", do you actually mean "rectangle"? May 31 '21 at 8:40
• @pxeger the 2. is accidentally left there after I remove the line break between 1. blah 2. blah. Should be removed.
– tsh
May 31 '21 at 8:44
• @Bubbler changed to rectangle. I'm not quite sure about these words.
– tsh
May 31 '21 at 8:44
• @tsh A square is a rectangle with all side lengths the same, so m == n. Sometimes in English, "square" is used as an adjective to simply mean "having right-angled corners", which is quite confusing May 31 '21 at 8:46

# Is there a left-right connection?

Given a square array of 0s and 1s, determine whether or not there exists a path of 1s connecting the leftmost and rightmost columns. A path can take steps of one unit up, down, left or right, but not diagonally. Every symbol on the path must be a 1, and it must start somewhere in the first column and end somewhere in the last column.

Shortest code in each language wins.

## Examples

000
111   ->  True
111

110
110   ->  False
110

101
010   ->  False
101

0     ->  False

1     ->  True

11110
00010
01110 ->  True
01000
01111

11110
00010
01100 ->  False
01000
01111


## Notes

The array may be represented in any reasonable form, such as a list of lists [[0,0,0],[1,1,1],[1,1,1]] or a string '000 111 111'`. It can optionally be in transposed form (so that the roles of rows and columns are exchanged; equivalently the code can instead determine whether there is a top-bottom connection). Any two distinct symbols can be used in place of 0 and 1. The output can be in any truthy/falsy form.

# Consecutive Distance Rating code-golfarray-manipulationinteger

Posted

• This is really neat! Simple, elegant, but nontrivial. It'd be interesting to look at the sum and its growth given an (OEIS) sequence. Jun 12 '21 at 1:25