# What is the Sandbox?

This "Sandbox" is a place where Code Golf users can get feedback on prospective challenges they wish to post to the main page. This is useful because writing a clear and fully specified challenge on 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.

To add an inline tag to a proposal use shortcut link syntax with a prefix: [tag:king-of-the-hill]

# The Minigame Challenge

The idea of this CnR is fairly simple: The Cops must create a simple minigame (explained in more detail below), with a definite goal. That goal may or may not be achievable. The Robbers must then either complete the minigame, or prove its goal is not achievable.

## Rules

### The Minigame

The Cops will create a suitably simple minigame with a definite goal.

Acceptable minigame examples are functions that take some input and return some output, with the goal being to either achieve a specific output, or make the program terminate or error.

Minigames considered complex (and thus unnacceptable) would be programs/functions that will never terminate in up to 60s (using TIO as a benchmark here), or that simulate complex games (such as blackjack, chess, etc).

### Cops:

The Cops must provide one of the following:

• A solution for your minigame that achieves the goal, or
• A proof that the goal for your minigame is not achievable.

at least 7 days (168h) after the answer was posted for their answer to be considered safe.

If your minigame's goal is achievable, it must always be achievable, and it must not contain "insider information", such as a fixed seed for a pRNG, or pregenerated primes as factors of a number to be factored.

### Robbers:

To crack an (unsafe) answer, the robber must provide either a solution to the minigame that achieves the stated goal, or a proof that the goal is not achievable.

abcdefghijklmno
pqrstuvwxyz{|}~

¡,,#$%⅋,)(*+'-˙/ 0ƖᄅƐㄣϛ9ㄥ86:;>=<¿ @∀qƆpƎℲפHIſʞ˥WNO ԀQɹS┴∩ΛMX⅄Z]\[^‾ ,ɐqɔpǝɟƃɥᴉɾʞlɯuo dbɹsʇnʌʍxʎz}|{~  The rest of the characters are kept as-is(yes, the unprintable characters are in the ASCII character set). The characters that are larger than 0x7f will be mapped back by subtracting the character code by 128. If you are using a character that is larger than 256, modulo the character's character code by 128 before checking the availability. ## Rules • No standard loopholes, please. • Input and output will be taken with our standard input methods. • If you force Jono 2906 to change a key on their keyboard (allowing typing your specified character), you will get a penalty of +2 bytes for every key you add. • I don't think I quite follow. Are we given a character as input and need to output the upside-down version? – AdmBorkBork Aug 27 '19 at 14:06 • (1) I still find the question confusing even as to the basic functionality required. The "Input/Output" section seems to me to say that it's a Kolmogorov problem, but the "Rules" section talks about input. (2) If a character remapping is involved, the question should list Unicode codepoints for the characters in question, and should list test cases with Unicode codepoints. (3) Is the last rule saying that the program must work as is and after mangling? Or is it just a gimmick ("Post your code upside down, but it only has to work the right way up")? – Peter Taylor Aug 28 '19 at 8:39 • "The rest of the characters are not kept as-is(yes, the unprintable characters in the ASCII character set)." should this not be there? As for that entire paragraph, if I understand correctly: unprintable characters < 33 (as well as 127) will be kept as is; printable ASCII characters displayed will be converted to upside down; other printable ASCII characters and any character above 127 will be modulo-128 before doing the same check. – Kevin Cruijssen Aug 28 '19 at 9:24 • As for the last rule: we can only use those upside down characters in our source code, and when converting it to regular it should also work? So both programs ABC and ∀qƆ should work exactly the same? – Kevin Cruijssen Aug 28 '19 at 9:25 ## Wrong position I typr re;atively accuratrly, but so,etimes I made a whole nlock of text illegible by shifting a key right. So I need a program that corrects my text back to its original meaning. ## Rules • You have to left shift on a standard English QWERTY keyboard. • Whitespace do not count for the procedure before left-shifting and are kept as-is in a standard left-shifting procedure. If the key is the leftmost letter/symbol on a keyboard(i.e. The ~key, Q key, A key, Z key.), the key is kept as-is. If you reach a control character while left-shifting (Caps lock and Shift), their effects will not be triggered and the character before left-shifting is kept. • This is a contest; the shortest answer wins. • Both the input and the output shall be given via our default methods. ## Representation of a subset of the QWERTY keyboard that you will need The two lines connected are possible values of the key: shifted/unshifted. ~!@#$%^&*()_+
1234567890-=

QWERTYUIOP{}|
qwertyuiop[]\

ASDFGHJKL:"
asdfghjkl;'

ZXCVBNM<>?
zxcvbnm,./

(Space)
(Space)


## Input

The input will always be a non-empty string conforming the rules above.

## Output

The output will be the input string corrected to the originally intended meaning.

## Examples:

Yjod ,sfr yjr, imjsppu/ -> This made them unhappy.
vpfr hp;g -> code golf


## Feedback

I think this is not a duplicate; however, is any part of this challenge unclear or needs improvements?

• I think you are mixing up left and right. Clearly, ~, Q, A and Z are leftmost keys, NOT rightmost. And your examples appear to be left-shifting, not right-shifting. – wastl Sep 7 '19 at 11:27
• "I think this is a duplicate" - so why sandbox it? Or did a not go missing in editing? – Peter Taylor Sep 9 '19 at 8:36
• Thank you. Predominantly my mouse was not working again, I didn't get around to fix this. – user85052 Sep 9 '19 at 8:56
• "sonetimes" and "vlock" are shifted the wrong way. – Hiatsu Sep 9 '19 at 16:20

# Path to Path Rearrangement

In the xkcd comic "Map of the Internet", a special fractal path was used, similar to this:

0  1  14 15
3  2  13 12
4  7  8  11
5  6  9  10


Ascii art version:

-0---1  14---15--16 19--20---21
|   |       |   |       |
3---2  13---12 17---18 23---22
|           |           |
4   7---8   11 30---29 24---25
|   |   |   |   |   |       |
5---6   9---10 31  28--27---26
|
58---57 54---53 32  35--36---37
|   |   |   |   |   |       |
59  56---55  52 33---34 39---38
|           |           |
60---61 50---51 46---45 40---41
|   |       |   |       |
63---62 49---+---47 44--43---42
\|/


This path, known as the Hilbert curve, has some interesting properties. Among other things, it can be flipped diagonally without changing most of those properties.

-0   3---4---5  58--59---60  63->
|   |       |   |       |   |
1---2   7---6  57---56 61---62
|           |
14---13  8---9  54---55 50---49
|   |       |   |       |   |
15  12--11---10 53--52---51   48
|                           |
16---17 30---31--32--33 46---47
|   |           |   |
19---18 29---28 35---34 45---44
|           |   |           |
20  23---24  27 36  39---40  43
|   |   |   |   |   |   |   |
21---22 25---26 37---38 41---42


Your task is to apply this transformation. Given a space on one path, find the corresponding location on the other. For example, the fourth space in the top path is located at (0, 2), which is the 14th space along the second path, so the correct output for 4 is 14.

As with similar challenges, this can be done as:

• An infinite sequence along the second path of the corresponding locations along the first path
• A function/program that takes a numbered position on the first path and returns the distance to that point on the second path.
• A function/program that takes a numbered position on the first path and returns all path 1 positions along path 2 to the point specified.

The first 64 terms of this sequence (zero indexed, add one to each for one indexed) are:

0 3 2 1 14 15 12 13 8 11 10 9 6 7 4 5 58 57 56 59 60 63 62 61 50 49 48 51 52 55 54 53 32 35 34 33 46 47 44 45 40 43 42 41 38 39 36 37 26 25 24 27 28 31 30 29 18 17 16 19 20 23 22 21


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

## Meta Questions

• Do I need a better description of the paths?
• Is the challenge itself clear?
• Any other issues I should fix before posting?
• The default output formats for sequence challenges can be found in the tag wiki – Jo King Sep 10 '19 at 4:03
• (1) Related. (2) I don't find "Find the location along the second path of a point on the first path" at all clear. It seems to be talking about output in 2D. I think it would be clearer to say "Given an index on the first path, output the index of the same coordinate on the second path". And then give a worked example (e.g. 4 vs 14). – Peter Taylor Sep 10 '19 at 10:53

# Is this number part of a Collatz Prime sequence?

Each step of a Collatz Sequence can be summarized as:

$$p_{2} = \frac{3*p_1+1}{2}$$

Where p1 is the input number, and p2 is the output number.

You task is to find where both the input and output are primes.

Here are some test cases:

1  -> (3*1+1)/2 = 4  : false
3  -> (3*3+1)/2 = 5  : true
5  -> (3*5+1)/2 = 8  : false
7  -> (3*7+1)/2 = 11 : true
11 -> (3*11+1)/2= 17 : true
15 -> (3*15+1)/2= 23 : false
91 -> (3*91+1)/2=137 : true
97 ->(3*97+1)/2 = 146: false


Output should be some truthy value, and false may be an error.

• 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? – Peter Taylor Sep 13 '19 at 10:56
• @PeterTaylor are they not the same thing? – Pureferret Sep 13 '19 at 11:09
• Alternative phrasing: which of $p_1$ and $p_2$ are you calling a Collatz prime? – Peter Taylor Sep 13 '19 at 11:11
• @PeterTaylor I mean $p_1$ – Pureferret Sep 13 '19 at 11:22
• So neither the input prime nor the Collatz prime need to be prime? – Jonathan Frech 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? – Jonathan Frech 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. – Pureferret Sep 17 '19 at 10:55
• To me it feels like an unnatural extra constraint. – Jonathan Frech Sep 17 '19 at 12:54
• @JonathanFrech it's just defining how to behave with certain inputs. – Pureferret Sep 18 '19 at 9:12
• Citing Exceptional edge cases; such out-of-place definitions are generally frowned upon. – Jonathan Frech Sep 18 '19 at 9:56
• @JonathanFrech I've changed the initial ask, and now it shouldn't be an exception – Pureferret Sep 18 '19 at 10:23
• Cf. A158709. – Jonathan Frech Sep 18 '19 at 10:53

## Maximize the Hello, world's in code permutations

In this task you should output this exact string: hi orb (because Earth is a sphere). However, here is the catch: you must output as many hi orb's as possible in all of your code permutations. Identical permutations do not count(e.g. aa's permutations count as one permutation)

Say you have a program abc that outputs this string. You should try your best to make acb, bac, bca, cab, and cba (i.e. the permutations of abc) also output this exact string.

## Rules

• Input/output must obey our standard methods.
• Your score is simply the factorial of the length of your code. You shall also present the following score: The score is counted in the negative of the length of your source code divided by the number of permutations that your code generates; (expression: -(source length/permutations).) Of course you want to keep your score as low as possible.
• All comment characters in your language are disallowed, in order to avoid collapsing into a radiation-hardening challenge.
• If you are using the filename as data, the filename must also count in the permutations.
• The source code length should be <1000. (Don't ask why, it's just an attempt of avoiding abusing the source code length.)

## Feedback

• Is it detailed enough?
• Is the input/output rules clear enough?

I don't think this is a duplicate because nobody has asked a question tagged with both permutation and hello-world. However, I worry that this challenge will collapse into a radiation-hardening challenge if you comment out a single character and then make sure that this will produce the same result, therefore making it a flavored version of this question and close to a duplicate.

• Can't you just extend your score by increasing your byte counnt, as long as you have some commented out part or no-op? – Jo King Sep 19 '19 at 8:50
• Unneccecary NOPs are disallowed, and at least 1 permutation of your code must only contain relevant code and nops. is rather vague, since no-ops aren't really defined, nor is this challenge really that possible to increase score if you don't have no-ops, otherwise it will turn into a duplicate of the normal Hello World question – Jo King Sep 19 '19 at 9:25
• This reminds me of a challenge I sandboxed a while ago, but deleted since it was clear it would produce only trivial answers – Jo King Sep 19 '19 at 9:27
• code-golf scoring usually has lowest score (=code length) wins. If you break with that convention, you should mention it in the rules. I think a big problem with this is that for any non-trivial answer (Like H in HQ9+), the proof of correctness of the score is almost impossible, because unlike radiation-hardening, the amount of variants increases factorially instead of linearly with the code length. – AlienAtSystem Sep 19 '19 at 11:52
• Hmm, it is okay, I will make the score negative then. I believe a program running the permutations of a string (not counting repeated ones) and evaluating them to check the result will be sufficient. Hmm, that's why the submittor needs to golf their code: to allow others to check their answers. – user85052 Sep 19 '19 at 12:09
• That's where it's unfeasible: The highest-scoring answer in the challenge you linked has 96 bytes. That's 9.9*10^149 permutations to check if they output the correct result. Even assuming your implementation is the fastest possible, that would take years, just for that single answer. You can't brute-force determine the score, but using mathematical trickery to try and calculate the score by hand will be arduous and prone to errors. – AlienAtSystem Sep 19 '19 at 13:10
• I don't think the limitations you have put are going to prevent this from falling apart. For example, this Pyth program works for any permutation of the code where only characters after the third " are permuted. Completely filling up the code allowed will achieve a score exceedingly close to zero. I don't think that is what you want, but I'm not really sure you can fix it (like what happened to Jo King), sorry. – FryAmTheEggman Sep 19 '19 at 18:38
• @FryAmTheEggman this particular snippet fails the rule that all code needs to be relevant. However, even if we tighten the rule to all code being life and necessary, that is, in one permutation, all code is executed, and a deletion of any statement resulting in the code not outputting "Hello World" any more, you can still cheese the challenge by bloating the code. The only way to stop that would be to change the scoring method to also use the factorial of the byte count, but then A) HQ9+ is unbeatable and B) It's a math challenge because you have to calculate the amount of viable permutations – AlienAtSystem Sep 20 '19 at 10:06
• Instead of helo word, wouldn't it make more sense to just use a different phrase like greeting earthlings or something along those lines? I agree with @AdmBorkBork that helo just looks weird. I do think it shouldn't be hello world to prevent builtins, so helo word is already better, but it still looks weird and will raise questions for sure.. – Kevin Cruijssen Sep 20 '19 at 12:38
• I don't understand the scoring. If we're scored only on the factorial of the length of code, why does it matter how many permutations output hi orb? I would figure that the number of ways that is output should factor into the scoring somehow... – AdmBorkBork Sep 20 '19 at 14:11

# The Celestial Bureaucracy king-of-the-hill

Posted

• This sounds like a lot of fun. When the exam is asked, is it possible to know which bot gave the exam? – Pureferret Sep 18 '19 at 11:58
• You are given the ID of the bot via the parameter for ask, which allows you to identify if you've interacted with that bot before and if it's the Jade Emperor (because his ID is always -1). You won't get the name - if you want to identify the bot, you'll have to analyse its question and answer pattern. – AlienAtSystem Sep 18 '19 at 12:08

# Creep Spread Territorial Control (WIP)

(probably)

Blah blah blah flavor blah blah blah something about Starcraft blah blah blah

# Gameplay

## Initial State

There is a 150x150 grid of square cells with approximately 7500 random cells missing in a symmetric Perlin noise pattern. There are four creep spread factions competing for dominance of this territory beginning as a single cell 10 cells in from a corner of the grid (one faction per corner). Each faction starts with 50 energy. The board does not wrap around at the edges.

## Expansion

Each turn, each faction earns 1 point of energy for each controlled cell plus 20 base energy. This energy is used for expansion. How much a cell costs to expand to depends on how many cells controlled by the same faction are in the Moore neighborhood of the target cell.

• 0 neighbors: cannot expand to this cell
• 1 neighbor: 50 energy
• 2 neighbors: 20 energy
• 3 neighbors: 12 energy
• 4 neighbors: 8 energy
• 5 neighbors: 5 energy
• 6 neighbors: 3 energy
• 7 neighbors: 2 energy
• 8 neighbors: 1 energy

There is no limit to how many cells can be expanded to in one turn other than energy costs. All expansions occur simultaneously. If two or more factions attempt to claim the same cell on the same turn, the one with the most neighbors of its own faction will claim the cell. If there is a tie, none of the factions claim that cell. Players whose expansions failed due to competition will not be refunded. Factions may expand onto each other's territory, stealing ownership of the cell.

## Game End

The game lasts 10,000 turns or until there is only one faction remaining, whichever happens first. The winner is the faction with the most owned cells. Ties are broken by remaining energy.

The overall winner will be resolved with a randomized pool where each bot plays an equal number of games followed by 12 games of the top 4 contenders. (one for each possible corner positioning)

# Coding

Write a bot that plays this game

• Bots must be deterministic. As a way to provide localized pseudorandomness, a random integer between $$\0\$$ and $$\2^{32}-1\$$ will be passed to the bot, which will be seedable in the controller.
• Bots have perfect information of the current state of the board, which turn it is, and their own energy, but not the energy of other players.
• Bots may not remember anything between turns, but may initialize constants and utility functions at the beginning of each game.

The list of desired expansions is ordered. As soon as an invalid expansion target cell is encountered (whether by cost or lack of same-faction neighbors) in this list, the rest of the list will be ignored and a warning will be logged.

• So if I build at 0,1 and 1,0 on the same turn while having a cell at 0,0, the cost would be 2000, yeah? Are failed expansions refunded? Also, I think having a source of randomness would be good. – Veskah Sep 13 '19 at 17:40
• @Veskah, that would cost 2000, correct. I'll add some rules about when failed expansions are refunded. – Beefster Sep 13 '19 at 19:38
• Suggestions: 1. Maybe allow expanding to own territory too? Could be used as a defensive mechanism when you can predict that you are going to be attacked. (should be thought about, could be bad) 2. Maybe set a limit on how many cell expansions can happen per turn to avoid exponentially expansion? I'm thinking that a bot which gains some advantage might get unstoppable when it is unlimited. – Night2 Sep 14 '19 at 7:33
• 3. More clarification in rules about expansions, for example if player 1 and 2 have a tie on this turn for cell X and they both go for it, but player 1 also goes for a neighbor of cell X in same turn, will player 1 win? (@Veskah mentioned another scenario too) 4. I would suggest using JavaScript so more people can write and run the code (anyone with a browser can do it), also a controller with some helper functions could be nice, for example a function which returns expansion cost for a cell in an optimized way to avoid tens of different implementations for same common action. – Night2 Sep 14 '19 at 7:39
• 5. "Bots have perfect information of the current state of the board.", does this include current energy value of other players? – Night2 Sep 14 '19 at 7:45
• @Night2 1 Interesting. It seems a bit fiddly. 2 This should actually come out to a quadratic expansion rate since where you can expand to is derived from perimeter, which grows linearly. 3 All expansions are resolved simultaneously (as in Conway's Game of Life), so player 1 does not win that tie. 4 Javascript is the likely plan since I intend to have a significant graphical component. 5 I'll have to think about it. That could be rather interesting as 'private' information. – Beefster Sep 15 '19 at 3:00
• 6. Proposal to spice things up: board is randomly generated, with some cells being unavailable for expansion. Uniform random, Perlin/Simplex noise, cellular automaton-based cave generation, etc. 7. Will the bots have access to the turn counter? 8. Maybe rotate and/or mirror the board provided to the bots so that each bot starts at, for example, the top-left corner from its perspective? – Alion Sep 15 '19 at 10:36
• 9. Allow bots to pre-calculate some data on load or game start. This will allow people to speed up their bots. Especially useful if you end up implementing 6. – Alion Sep 15 '19 at 10:47
• @Alion 6 That sounds pretty interesting. I'll probably expand the board slightly in that case. 7 Yes, they'll know what turn it is. 8 I don't think that adds much. I'm probably going to have to make copies of the board every turn anyway to make it impossible to cheat on accident though... 9 Seems reasonable. – Beefster Sep 16 '19 at 0:39
• "Bots must be deterministic. As a way to provide localized pseudorandomness, a random integer ... will be passed to the bot, which will be seedable in the controller.". Why not make a custom random function available or override the default random generator and make the controller generate and handle the seeds? For example in JavaScript users can still use the normal Math.random(), but you can use this to make it deterministic: davidbau.com/archives/2010/01/30/… – Night2 Sep 21 '19 at 11:21
• @Night2, yeah. I'll probably do that since I'm going to have to use an RNG library anyway. – Beefster Sep 22 '19 at 2:32

# Turing-complete regex subset

It's widely known that a programming language is one iff it's capable of addition of natural numbers and primality testing. In practice, this criterion has a high accuracy for distinguishing Turing-complete languages too.[citation needed]

## Cops' challenge

Choose any of the programming languages available on tio.run. Write a regex that will define a subset of this programming language. The subset must still match the definition, though ideally this should be far from obvious.

Write two programs in this language that match this regex:

1. Take two natural numbers, a and b, as input. Output a + b. The program must work for 0 ≤ a + b < 215.
2. Take a natural number n as input. Output whether the number is prime. The program must work for 0 ≤ n < 215.

The behavior outside of this range is undefined. This means that you can output the correct answer, a cute cat ASCII art, an error, an invalid answer, invoke nasal demons, or anything else you can, or cannot, imagine.

Regex come in multiple flavors. Choose one. You can choose any flavor available on regex101, or Retina.

• the programming language and regex flavor you chose
• the regex delimiter and flags you chose (for example: //gm; does not apply to Retina)
• the regex you wrote and its byte count
• the byte counts of your two programs

## Robbers' challenge

Write two programs that prove the subset to be a valid programming language. The rules that apply here are the same that apply to the cops. Additionally, your programs must not exceed the cops' in length.

# Meta questions

The above will be posted as the cops' thread, with the robbers' thread simply linking to it.

• Any improvements to challenge structure? I've never done this before.
• Do you see any loopholes that need addressing?
• Are the allowed regex flavors reasonable?
• Duplicates?
• I think this is a duplicate of codegolf.stackexchange.com/questions/136150/… – pppery Sep 22 '19 at 18:11
• @pppery Hmm. These are definitely pretty similar. On the other hand, regexes might allow more interesting answers. – NieDzejkob Sep 22 '19 at 18:25
• I'm not convinced this is a dupe since most of the interesting work here is in selecting the regex rather than in choosing a sequence, though I think the other challenge is cleaner. I think the optimal scoring regex will usually be to make an "unhash" that produces the appropriate programs. Unfortunately I don't have any suggestions at the moment to help fix that, but if you can then I think this is alright. – FryAmTheEggman Sep 22 '19 at 18:32
• @FryAmTheEggman I can't see what you mean by "unhash" here. Could you elaborate? – NieDzejkob Sep 22 '19 at 18:36
• Consider this program which performs the first task. The regex that matches only programs like this would be short but but not very informative. I think doing this but making guessing the magic number arbitrarily hard would usually be the best approach in a given language. – FryAmTheEggman Sep 22 '19 at 18:43
• @FryAmTheEggman Like, /^\.vC\d+$/? I think that making it complicated enough would take quite a lot of bytes. – NieDzejkob Sep 22 '19 at 19:02 • The point is that the number could be manipulated, so I could pad my program arbitrarily until I got a number that let me write a regex like ^...(2|10|76|345?)*$`. That's neither very long nor easy to crack. – FryAmTheEggman Sep 22 '19 at 19:06
• I like the idea of the challenge but I feel including the bit about Turing completeness is a bit of a red herring, it only really distracts from the challenge. – Wheat Wizard Sep 22 '19 at 21:30
• To elaborate the particular part I like is regex selection part. I do agree that my challenge is a bit cleaner otherwise. – Wheat Wizard Sep 22 '19 at 21:31