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

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Solve a Quartic Equation

Since I saw the quartic formula and it's a behemoth to solve, your task is to implement it in as few bytes as possible. That's it.

To clarify some concerns, input and output can be as a string representing the equation, a list of numbers, numbers on different lines of STDIN/STDOUT, or a tuple of numbers - anything that represents clearly the four solutions is acceptable, and anything that clearly represents the five inputs is acceptable.

You may assume the equation will always have a real root, and if you choose not to support imaginary roots, you just need to output the real root(s).

On advice from TNB, builtins are now banned The formula for reference:

For a quartic equation $$\ax^4 + bx^3 + cx^2 + dx + e = 0\$$:

$$\x_1, x_2 = \frac{-b}{4a} - S \pm \frac{1}{2}\sqrt[]{4S^2 - 2p + \frac{q}{S}}\$$

$$\x_3, x_4 = \frac{-b}{4a} + S \pm \frac{1}{2}\sqrt[]{4S^2 - 2p + \frac{q}{S}}\$$

where:

$$\p = \dfrac{8ac - 3b^2}{8a^2},\$$ $$\q = \dfrac{b^3 - 4abc + 8a^2d}{8a^3}\$$

where:

$$\S = \frac{1}{2}\sqrt[]{-\frac{2}{3}p + \frac{1}{3a}\left(Q + \frac{\Delta_0}{Q}\right)},\$$ $$\Q = \sqrt[3]{\frac{\Delta_1 + \sqrt[]{\Delta_1^2 - 4\Delta_0^3}}{2}}\$$

and where:

$$\\Delta_0 = c^2 - 3bd + 12ae,\$$ $$\\Delta_1 = 2c^3 - 9bcd + 27b^2e + 27ad^2 - 72ace\$$

I learnt LaTeX just to do all those formulae. I hope you're proud of me. As always, this is , so shortest wins.

• Are we supposed to support non-real roots? May 17 at 23:37
• I had gave up to read these crazy formula and I will try some languages with a built-in to solve this...
– tsh
May 18 at 2:28
• "quartic equation: ax4+bx3+cx2+dx+e"; should be "ax4+bx3+cx2+dx+e = 0"
– tsh
May 18 at 2:28
• I cannot get the formula work. Had I made some typo?
– tsh
May 18 at 2:41
• @Arnauld yes - if your language can support it, it should. May 18 at 5:59
• I don't think that if your language can support it is a sound criterion, as any TC language can simulate complex numbers (although it can quickly turn into a nightmare with some of them). It may be better to just say "supporting roots with imaginary parts is optional" if that's what you decide. May 18 at 6:58
• OK - I'll make that optional - but would it be better to make that a bonus or just make it optional May 18 at 7:31
• @tsh Give me a second to check that May 18 at 7:35

Assume a standardized test has $$\15\$$ multiple choice questions, with $$\3\$$ options each. A school has some students and wishes for at least one of the students to get $$\10\$$ correct answers. Since no one in the school knows any math they are going to cheat and tell each student which answers he has to give without knowing what the actual correct answers are.

The problem is to find a number of students $$\n\$$ such that it is possible to do this and guarantee at least one of the students gets at least $$\10\$$ correct.

For example one way to do it is with $$\n=3\cdot2^{15}-1\$$ students, where we do all possible exams with at most two different options, since one of the options appears at most $$\5\$$ times we can get at least one test with $$\10\$$ correct solutions.

Another possible $$\n\$$ is $$\a^5\$$ where we can get a set of $$\a\$$ tuples of length $$\3\$$ that interesect every option of length $$\3\$$ at least twice ( so basically a solution to the problem with length $$\3\$$ and at least $$\2\$$ correct). It seems that the vectors $$\(1,1,1),(2,2,2),(3,3,3)\$$ along with the 6 permutations work, so $$\9^5\$$ is also a valid $$\n\$$.

The score will be $$\\frac{1}{n}\$$ where $$\n\$$ is a value for which it is possible to prove a configuration exists.

• I'm not sure this is on-topic on our site, since it is not explicitly about code. I think primarily mathematics-based puzzles are allowed on Puzzling.
– Wezl
May 26 at 15:09
• You think the best arrangement can be found with math? Without a lot of computation?
– user103863
May 26 at 15:10
• I'll admit that it might be ok to post it here with the tag code-challenge
– Wezl
May 26 at 15:12
• It seems like something which can be solved optimally with vertex cover, since 3^15 is reasonably small. May 28 at 6:11
• Actually it's set cover, not vertex cover. Maybe the best result would be from approximation algorithms, or maybe someone would be able to find a polynomial algorithm for this specific case. May 28 at 6:18

Posted!

Compute the generalised XOR (posted)

• $(b - ((p + q) \bmod b)) \bmod b$ can be simplified to $-(p+q)\bmod b$. May 28 at 4:00
• Yes, I was a bit worried about people getting confused about negative modulo, but I'll make that edit, it's probably easier to understand that way.
– xavc
May 28 at 4:02

Construct a Modulo Multiplication Table

• You could change it to be "consider a (n-1) x (n-1) ... and modulo n" (e.g. 5x5, taken modulo 6) so you don't have to ignore the last row and column Jun 2 at 13:47
• @pxeger Thanks. Any suggestions for the title? Jun 2 at 13:48
• short and simple: "Modulo tables"? Jun 2 at 14:00
• Usually I think of quadrants as axis-aligned.Maybe "Modulo multiplication table", maybe throw in the word partial.
– qwr
Jun 2 at 14:26
• Also more test cases just for good measure
– qwr
Jun 2 at 14:26

Salvage My Chemistry Homework

Introduction

I pulled an all-nighter yesterday doing my Chemistry homework. However, I now realize that was a terrible idea, because my handwriting was too sloppy and now I can’t distinguish the capital letters from the lowercase letters in my chemical formulas! This is a problem, because now the formulas can mean completely different things - for example, co could be cobalt or carbon monoxide. I want to know which of the formulas in my homework are ambiguous in this manner.

Since there are many formulas in the homework, I would like a program to help me so I don’t have to go over them all manually. Also, because the homework is due in an hour, I would like to have the code be as short as possible so I don't have to type as much.

Background

A chemical formula consists of one or more 'units'. Each 'unit' consists of a symbol of an element (the list of valid symbols is given in the input) optionally followed by a number greater than 1. For example, c, co and br2 are valid units (assuming that "c", "co" and "br" are in the list of symbols), while c0 and br2r are not valid units.

Input

The input consists of

• The list of elements (all letters are lowercase)
• A chemical formula with all letters in lowercase

Output

Output an integer, the number of ways there to separate the formula into individual units.

Test Cases

Input: ['c', 'o', 'co'], 'co2'
Output: 2 ('c o2', 'co2')

Input: ['c', 'h', 'o', 'ch', 'oh'], 'ch3cooh'
Output: 4 ('c h3 c o o h', 'c h3 c o oh', 'ch3 c o o h', 'ch3 c o oh')

Input: ['c'], 'c1'
Output: 0 (1 is not a valid subscript)

Input: ['a'], 'co2'
Output: 0 ("c" and "co" are not valid symbols)

Input: ['n', 'h', 'o', 'nh', 'no'], 'nh4no3'
Output: 4 ('n h4 n o3', 'n h4 no3', 'nh4 n o3', 'nh4 no3')


Standard loopholes apply. All reasonable input and output methods are allowed. This is , shortest code in each language wins.

Meta

• Would it be better to output each way to split the formula or just the number of ways?
• Any general wording improvements?
• Anything I should be more specific about?
• Suggested tags?
• Given that l4m2's question has now been posted, should I remove this? (While the challenge is similar, there are some significant differences).

Credit to l4m2 for original idea

Closest Binary Fraction

For this challenge, a binary fraction is a fraction where the denominator is a power of two. Your program (or function) should take a rational number as input, and return the nearest binary fraction with a given denominator.

Input:

The first input will consist of a rational number. This can be represented by any of the following:

• A floating point number, or built-in rational type
• A fraction, either as a built-in rational or fraction type, or represented as a pair of numbers
• A decimal string, in any chosen base

The second input is an integer $$\d \ge 1\$$, representing the denominator of the binary fraction.

Output:

Output must be able to represent the exact fraction. This means any of the input formats for fractions are valid, as long as they can reasonably represent any valid outputs.

You may choose if you want to simplify the output. Given the fraction 9 / 19 and the denominator 8, either 4 / 8 or 1 / 2 would be accepted.

Test cases:

Other:

This is . Unfinished and also a dupe of a newer challenge of mine

• the output part seems.. unfinished? Apr 30 at 2:47
• @Razetime It is, yeah. I was halfway through drafting this when I had to go work on something else, so I just left it here as a reminder to finish it :p Apr 30 at 3:21

Is it a Fischer random chess starting board?

• Scoring? (code-golf?) Tags? (string chess decision-problem?) Jun 2 at 14:11
• @pxeger yes. I always forget to put them in these posts
– qwr
Jun 2 at 14:12

You are an angry dude who manages the servers, but you are terrible in it. People often text you, and sometimes they ask why are the servers down - you got very annoyed!

Given a non-empty string. If it contains "server" and "down" (capitalization doesn't matter), you infinitely output the >:( face with a newline after. If it doesn't, you only output "Hi" once, because you are busy and angry.

Examples

server down -> >:( (infinitely)
server -> Hi
down -> Hi
serverANDLETTERSAFTERTHEWORD down -> >:( (infinitely), as it contains both server and down
Why are your servers down? -> >:( (infinitely)
sErVeR dOwN -> >:( (infinitely)
serverDowN -> >:( (infinitely)
serverd0wn -> Hi

Rules

• This is , so the answer with shortest bytes wins.
• These loopholes are, obviously, forbidden.
• Standard code-golf rules apply.
• Please specify the language you are using and the amount of bytes.
• It would be great if you would put a link to a sandbox where your code can be ran in action, such as TIO.
• Explaining your code is very welcomed.

Please comment down below if this is good enough or not, or if it's a duplicate (hope not)
• I don't want to discourage you, but this seems a little trivial and uninteresting to me. Of course, that's just my opinion, and others may enjoy answering this challenge. For the output, would a an infinite list of characters be okay?
– user
Jun 6 at 18:20
• It seems like combine two tasks together: 1. test if a string contains both two words or a not; 2. implement a truth machine
– tsh
Jun 7 at 8:21
• Damn, that question looks very similar Jun 7 at 8:23

Ambiguous Chemical Formula

• This looks like an interesting challenge, but in its current form needs a lot more details (as do most of your sandbox posts - I'd recommend using a question template to make sure you've always included everything). For people who don't know chemistry, it's lacking crucial information: what is the exact syntax of a chemical formula, and how does one know it's ambiguous? Apr 22 at 16:28
• I also think it would be more interesting if the element list were provided as input. Otherwise most of the actual golfing part of the challenge boils down to compressing the list (or finding a short built-in to output them) Apr 22 at 16:29
• @pxeger Quite unrelated to chemical though, ClI and CLi both don't fell good
– l4m2
Apr 22 at 18:23
• I've edited this down to a stub now that it's been posted to save space Jun 7 at 1:01

• Also, I'd love some advice on how to specify what to do for some of the more "exotic" languages. e.g. C and such will obviously just use function-pointers… but I really don't want to alienate any Jelly golfers; those solutions are always my favorite! May 20 at 15:49
• Even function-pointers in C wouldn't help afaik, because you can't dynamically construct the function. Maybe you should allowed output the source of G, or alternatively make R take m and pk and just function directly as G. May 21 at 7:48
• @CommandMaster Thanks for the feedback! Would defining R(digest, pk) work? Such that it gets composed: R(φ(m), pk) -- (this would also align better with the way the original paper defined them.) May 21 at 14:08
• I think it would work, and it's also good because it lets programming languages without the concept of a "function" participate May 21 at 14:15
• @CommandMaster How's the current setup look? I'm certainly worried about accomodating languages without functions. Especially Jelly; I'm not really sure how it works, but I always enjoy those answers a lot! May 21 at 14:39
• I've edited this down to a stub now that it's been posted to save space Jun 7 at 1:02

Write a netquine

There are a lot of online interpreters, for a lot of languages. For example, there's the ubiquitous TIO, but there are also smaller, more specific ones that others have made, such as interpreters for Vyxal, ngn/k, or Grok.

Your goal today is to write a netquine, or a program whose output, when used as a URL, leads to that program in an interpreter for that language. Essentially, if you have a link to your program, and the program outputs that link, it's valid.

For example, say you write a Vyxal program λλλλ. In the Vyxal interpreter, if you press the button to generate a permalink for this program, you get:

http://lyxal.pythonanywhere.com?flags=&code=%CE%BB%CE%BB%CE%BB%CE%BB&inputs=&header=&footer=


However, due to the way that the interpreter processes links, you could also leave out the blank fields:

http://lyxal.pythonanywhere.com/?code=%CE%BB%CE%BB%CE%BB%CE%BB


You can even replace the HTML character codes with the actual characters:

http://lyxal.pythonanywhere.com/?code=λλλλ


All of these are valid links to the Vyxal program λλλλ, and therefore would all be valid outputs for a netquine.

• Obviously, Standard loopholes are forbidden.

• Even though URL shorteners are forbidden by default, shortening a URL, like in the example, is fine, as long as it still leads to the right place.

• For the purposes of this challenge, a web browser may be considered an "interpreter" for HTML and/or CSS. This means you might be able to do something along these lines.

• Usual rules apply, as do usual rules.

• This is , so the shortest answer in bytes wins!

Meta

• Is this question clear enough?

• Should I change the scoring to accommodate the potential differences in URL length? (lengths of domain names, different ways of generating links, the ability to shorten links, etc.)

• Any other feedback?

• This question is quite similar, but it only allows for TIO languages, and it doesn't allow any sort of shortening, even if the link is still valid (there was a comment asking about that), so I would consider it to be related, but not a dupe.

• Interesting idea, but you won't get many answers because most online interpreters use an external compression algorithm to shorten the hash (and then base64 it), which is quite lengthy to implement from scratch. Note that the existing answers on the linked challenge all use a gzip or zlib builtin. Jun 9 at 23:12
• You should provide a list of valid online interpreters, as someone could just make a.com lead to an interpreter for a program in some language that outputs https://www.a.com. Also, please define "in" in the sentence "leads to that program in an interpreter". Does the HTML of that page simply have to contain the program? Jun 9 at 23:40

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 at 8:29
• What is the meaning of the 2 in A_{m×n}2? May 31 at 8:37
• Related May 31 at 8:39
• When you say "square", do you actually mean "rectangle"? May 31 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 at 8:44
• @Bubbler changed to rectangle. I'm not quite sure about these words.
– tsh
May 31 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 at 8:46

Encode USB packets code-golfbinarycoding-theoryencoding

Posted

• Is the fifth example correct? Shouldn't 11111111 (8 ones) be JJJJJJKKK? If not, how is 11111111 distinguished from 11111101? (This also applies to your other challenge). Jun 6 at 19:33
• @Spitemaster yep, you're right - fixed. Jun 9 at 14:33

A Cat’s Game to Claim

Posted

• Any catchy name suggestions also appreciated! "Proclaim" rhymes as well, but I can't get it to roll of the tongue. Jun 12 at 1:15

Build a raw string

In this challenge you will write code which, given a single line string as input, can output the raw version.

Full spec

The input will be a string like ab\n or ab\u0065e\\ or e\'543. These strings should be converted to a raw version which uses the backslashes.

This probably sounds confusing, so here is a more complete explanation.

The most common form of strings used is simply a quote (one of ', " or the backtick), followed by a sequence of unicode characters, then a closing quote which corresponds the opening one. "abc" or 'THIS is a St%ing', for instance. Note that this is not the case in all languages, for instance most golfing languages do not represent strings in this manner.

However, it's not that simple. Backslashes allow for much more complex strings, and their importance in allowing certain characters means a string like 'ab\' is invalid as the backslash "escapes" the quote. Making a backslash appear in a string requires \\ instead.

Also, quotes can be escaped via \', \" or \. A sequence like \\" should become \" while \"\ is invalid.

The newline and tab are both important, and so most mainstream languages have the \n and \t which are actually 1 character each, representing the newline and the tab, respectively. So \\t\"\n becomes

\t"



(note the trailing newline)

To add an extra layer of usability for "exotic" characters, it is possible to use a unicode escape: of the form \uxxxx where each x is one of 0123456789abcdef. This transforms into the unicode character whose codepoint is equal to the base-10 equivalent to the hexadecimal number xxxx. For instance \u0031 becomes 1 because 31 in hexadecimal is 49 in base 10, and 1 has a codepoint of 49.

Your input string may contain any of these escapes, and you may assume that \ is followed only by the backtick or any of \'"tnu. The unicode escape sequence is guaranteed to be valid, and escapes as well.

You should output this string after the transformations described.

Worked example

Input string:

ab%\u0035e\n\n\t5\'e\\54c%&\u0095


The first three characters remain identical.

\u0035 becomes 5 because 35 in hex -> 53 in base 10, and String.fromCharCode(53) === '5'.

\n\n\t becomes two newlines followed by a tab.

5 remains 5.

\' becomes ': escaped by backslash

e remains e.

\\ becomes \.

54c%& stays the same.

\u0095 is an unprintable with codepoint 149.

Result:

ab%5e

5'e\54c%&<unprintable>


(<unprintable> is an actual unprintable character) Note that functions capable of evaluating such strings are disallowed. To be clear, your program must handle the syntax described above, and not any other format.

Other test cases:

Input Output
\'\" '"
\\"\' \"'
\\u0031\u0031\\t \u00311\t
\\\\\\\\\n \\\\<NL>

[<NL> is newline]

Meta:

• Duplicate? Couldn't find anything.
• Any clarifications needed?
• Better title / tags?
• A bit unclear to me: Do we need to handle the string syntax of the answer's implementation language, or the syntax you specify here? If that of our own language, then what if our own language has few special characters? (E.g. in the APL family, it is common that the only unusual character in a string is the quote, which must be doubled.)
Jun 14 at 11:54
• "eval functions or similar are not allowed." but what constitutes being similar to eval? What about functions in the JSON object of JavaScript? What about library functions to do this? Does APL's built-in ⎕JSON utility function constitute an eval, though the language's real eval is ⍎?
Jun 14 at 11:56
• @Adám In some calculator questions, the OP (wisely) decides to disallow eval functions. Basically these functions. In essence, from my point of view, if your language is capable of evaluating these strings, then the function that does them is disallowed. However since APL's eval seems different, you can use them. Also in response to the one asking about string syntax, you must handle the one in the question, otherwise it gets a little unfair.
– user100690
Jun 14 at 12:06
• Will the input include surrounding quotes?
Jun 14 at 12:56
– user100690
Jun 14 at 13:01
• Then do we have to handle unescaped ' and/or "?
Jun 14 at 13:03
• @Adám You still have to handle them, just not surrounding the entire string.
– user100690
Jun 14 at 13:08
• Suggested test cases: '" and \'\"
Jun 14 at 13:09
• @Adám You know what, the idea of not having surrounding quotes is a little confusing, so I'll remove that rule. That means that your suggested test cases are identical to each other, so I'll add the latter to demonstrate. Also will add about five more cases.
– user100690
Jun 14 at 15:28
• "if this string were to be enclosed in quotes in your language and parsed as an expression, no errors should show." makes it sound as if my language matters.
Jun 15 at 15:35
– user100690
Jun 15 at 15:37
• Am I allowed to use \n in my code to insert a newline, or is this considered "functions capable of evaluating such"?
Jun 15 at 15:58
• – user100690
Jun 15 at 15:59

COBOL(lite) interpreter.

Your task is to code an interpreter for COBOL. This interpreter should use the free format, and cut a few corners, as long as a few test scripts will run on it.

Notice; here I say interpreter, as that is the general direction of my inclination, however if it may save bytes, a compiler would also count.

Try to:

• Golf your code as much as possible
• Remove some parts of COBOL (But ask here first to see if they make sense to remove.
• Accept both CAPITAL and lowercase

Avoid:

• Standard Loopholes
• Don't remove too many parts of COBOL. I think that IDENTIFICATION DIVISION. could be ignored, but DATA DIVISION. is probably necessary.

If there is a thing that you would like to clarify on, ask in the comments. I think that this question still could stand with improvement, before it can be added to the main cg se.

• You need to be a lot more specific with what you want implemented. This can range from syntax requirements to required keywords and function. You need to specify anything and everything yo want in a possible golfed interpreter. Jun 15 at 10:39
• I recommend checking questions tagged under interpreter on the main site for guidance. Jun 15 at 10:40
• @Razetime I didn't have a lot of time to make this post, but that is why it is in the sandbox. I know that I will need to improve it a fair bit, before putting it on the main code golf se Jun 15 at 23:17

Implement a feature-rich calculator

We have a few many calculator challenges on this site, but none seem to require a complex one with many different features.

This challenge is about emulating my old Casio calculator, except with no digit limit. Features are:

• basic (start with a single operation, then input the next operation)
• all clear (AC) which starts a new "calculation". No need for C.
• errors for dividing by zero (otherwise there should be no error)
• memory: M to set the memory to current number, MC as an inline expression representing the memory, and M- to get rid of the memory.

This should operate either on STDIN (prompt for commands each time) or in a function (taking in either a list of commands or a newline-separated string with commands).

Spec

Your solution should be able to handle floating-point numbers, hence float division should be used regardless of context.

When first run, the calculator will be "ON". It is guaranteed that input syntax is valid.

The chain of commands begins with a number operation number-like structure, where number can be replaced with MC to represent a reference to the memory. For instance 5 * 5 or 6/MC. Whitespace can be ignored or forbidden, that can be your call, but whatever it is you may assume syntax is valid.

Then, if your submission is a full program, it should output the result of that operation, or if a function, append that to the end of a list.

Subsequent operations can either be:

• M this sets the memory to current number. Memory can only ever hold a single number at a time.
• AC. Clears the current calculation and resets the number. Memory, however, will still be accessible.
• M-. (M minus) This clears the memory, and calls to MC will never be given when there is nothing in the memory.
• operation number where operation is + - * or /, and number is a number which can be replaced with MC.
• Off. The command Off stops the program, and it is reasonable to assume that no commands will be passed afterwards.
• - (minus sign) negates current number. Outputs the new number.

Division by zero should trigger an error and restart the calculation. AC, M, MC and M- should output nothing. Memory can be overwritten.

Note that operation number operation number will never be given, and that all operations will be performed on non-negative numbers. (we have the negate operator for negative numbers)

Also note that this challenge is less about parsing / processing a string input and more about responding to different kinds of input.

Example

As a full program, but note that a function will have to take in an array of commands. There is a >  before each command, but in your version, it is not required.

> 5*5
25
> *4
100
> /200
0.5
> /0
ERROR (or some form of ERROR)
> 15*6
90
> M
> +MC
180
> AC
> 7-MC
-83
> -
83
> M-
> +5
88
> Off


Meta: is it a duplicate? any clarifications needed?

• Maybe use the [interactive] tag, and make it clearer that this is less parsing/processing a given string input and more responding to inputs as given Jun 18 at 14:16
• The "error" should not terminate the program, right? Would it be OK to, on error, print anything that is distinguishable from numeric output (say "X", "Inf", or "NaN"), or print something different across errors (e.g. "Inf" for 1/0, "NaN" for 0/0)? Jun 25 at 1:40
• @Bubbler Yes, that's fine. You can also output Inf for 1/0 and NaN for 0/0 like you mentioned.
– user100690
Jun 25 at 5:10

KotH - Floating Point Prisoners Dilemma

• Looks intriguing! How does each round work though? So one is coop, zero is defect, but what do the floats in between do? Look forward to hearing! Jun 11 at 2:33
• It uses an equation from the wonderful fellows at math.stackexchange.com to determine what the in-between states should do. I'm bad at explaining, so the equations in my (probably horrible) code are in the play function of the controller class in controller.py Jun 11 at 2:46
• @4D4850 Would you link to the question if you have it still?
– math
Jun 11 at 17:46
• It was actually closed, but here it is: math.stackexchange.com/questions/4152360/… Jun 11 at 18:27
• Understood it now, good challenge!
– math
Jun 12 at 8:39
• Should I post the question? Jun 17 at 19:08
• Posted on Main: codegolf.stackexchange.com/questions/229926/… Jun 17 at 22:14
• I've edited this down to a stub now that it's been posted to save space Jun 18 at 14:33

Convert codepoint to UTF-9

UTF-9 was an April Fool's Day RFC joke specifications for encoding Unicode suitable for 9-bit nonet platforms.

Challenge

Your task is to implement a program or a function or a subroutine that takes one integer, who represents the codepoint of a character, to return a sequence of integers that represents its corresponding UTF-9 value.

Examples

Numbers that begin with 0x are hexadecimal, begin with 0 are octal, end with b are binary. Otherwise, a decimal.

input: 0x41 or 65
output: [0101], [1000001b], or [65]

input: 0xc0
output: [0300]


Hint

Section 5.2 of RFC4042 has an example of the impmenentation.

Meta

Gotta need to clarify I/O format more.

• For clarity, I'd start octal constants with 0o. Also, an explanation of how UTF-9 works should probably be included here. Jun 19 at 1:39

Outputting Blum Integers

• I'd suggest using standard sequence rules (answers can choose $n$th, first $n$ or infinite output). I've also edited the challenge a bit, feel free to revert any changes you dislike Jun 18 at 14:29
• @cairdcoinheringaahing thanks for the suggestion, i'll apply it Jun 19 at 9:14

Do these points approximately make up a regular n-sided polygon?

The input is a set of integer coordinates. Take them in whatever form you want, e.g. a list of tuples or just a plain list. The question is: can you draw an n-sided regular polygon with vertices at the specified coordinates? n being the amount of coordinates provided. Answer truthy if yes, falsy if no.

The level of precision is in integers. That means you will have to round both the x and y values of the ideal polygons to the nearest whole values. Here's an example diagram:

The triangle has points at approximately (5,5), (4,9), (1,6). You can draw a regular triangle to fit these coordinates, even if the actual points of the triangle are not at quite the same coordinates.

The same goes for the pentagon. The coordinate set (3,1), (7,1), (8,5), (5,8), (2,5) makes up a regular pentagon-ish, accurate to whole values.

Any set of coordinates can make up an infinite amount of approximate n-gons. You answer truthy if there's at least one such n-gon. One way of thinking about it is to consider a unit square around each of the points, then determine if you can stretch a regular polygon such that every point falls within the squares.

Further ground rules:

• The coordinates will always be positive.
• They do not have to be in any particular order.
• Coordinate values will never exceed 1000.
• There will not be more than 10 coordinates.

Examples:

(5,5), (4,9), (1,6) -> true
(3,1), (7,1), (8,5), (5,8), (2,5) -> true
(1,1), (1,1), (2,1) -> true
(1,1), (2,1), (130,1) -> false

(42,42) -> true


(according to Wikipedia, a monogon is still a polygon, meaning any input is valid.)

(0,1), (5,10) -> true


(any two points make up a regular bigon so this should work for any coordinates)

(1,3), (1,3), (1,3), (1,3) -> true


(any set identical coordinates will always match an n-gon that's tiny enough to have all of its coordinates rounded to the same integer).

• I just found this question. It seems to be the same question but it is closed with no answers, and I think my requirements are clearer. Jun 16 at 12:12
• I don't think the current explanation addresses the question "How are we supposed to tell if the polygon is regular without knowing its exact coordinates?" I feel like there's some way to gradually constrain polylines, but not quite sure. Also, I think "One way of thinking about it is to consider a circle of half a unit around one of the points" should be "... consider a unit square around one of the points" instead. What is the expected output of (0, 0), (0, 2), (1, 1), (2, 0) (which is borderline square with (-0.5, -0.5), (-0.5, 1.5), (1.5, 1.5), (1.5, -0.5))? Jun 23 at 0:15
• @Bubbler Thanks for the comment. You are correct about the circle being a square! My mistake. And yes, that would be truthy. Jun 23 at 8:59
• @Bubbler regarding "how are we supposed to tell if polygon is regular" that's asking for an example answer strategy, not part of the question, is it? The question is whether there is any regular polygon where each point falls in those unit squares. That's almost an optimisation problem. It's not impossible, all the required information is there. But I could try to come up with one approach - but answers should not feel obligated to copy that approach because for this problem there would be many solution strategies. Jun 23 at 9:03

Find all paths

code-golf grid

Information

• Given a non-negative odd integer (let's call it $$\n\$$), find the number of all possible paths which covers all squares and get from the start to end on a grid.
• The grid is of size $$\n\$$x$$\n\$$.
• The start of the path is the top left corner and the end is the bottom right corner.
• You have to count the number of all paths which go from the start to end which covers all squares exactly once.
• The allowed movements are up, down, left and right.

Examples

1 -> 1
3 -> 2
5 -> 104
7 -> 111712
9 -> 2688307514
11 -> 1445778936756068

• More test cases would be needed. Is this oeis.org/A121788? Jun 27 at 15:24
• I dont think this is that problem in the link Jun 27 at 15:34
• Anyway, please include more test cases Jun 27 at 16:24
• Is this oeis.org/A001184?
– tsh
Jun 28 at 8:22
• yes it is @tsh updated! Jun 28 at 8:37
• === Looks good! === Jun 28 at 8:43

Alteration of a challenge that was considered too close to an older quasi-duplicate.

ISO Computus

from a signed integer year number provided as sole input
the integer number of the calendar week of Easter Sunday as sole output
with as few variables and as few arithmetic operations as possible.

Easter Sunday is determined according to the Gregorian Computus (as used in the all Western Christian churches, including the Catholic Church, and some others), for which there are several equivalent algorithms available, see Computus, Gent, Stockton and ESTRALGS.TXT. There are 35 possible month-day dates, from 22 March to 25 April.

The week of the year is specified by international standard ISO 8601-1: All weeks start on Monday; there are no partial weeks; the first week of the year has 4 January (or the first Thursday) in it. For more information see the Mathematics of the ISO 8601 Calendar. There are just six possible results, weeks 12 through 17. W17 will hardly ever occur – it has never occurred since 1583 at least.

Restrictions

• You may use all basic arithmetic operators, including addition, substraction, multiplication, division, integer division, modulo, rounding (with integer flooring and ceiling), exponentiation, logarithms.
• You may not use library functions that implement an algorithm for the Computus, like PHP's easter_date(), EasterSunday[year] from the Mathematica Calendar package or Easter from the R package timeDate.
• You may not use other predefined date functions, e.g. to find the day of the week or the week of the year.

Ranking score

Your solution must be an algorithm implemented as an executable script in a programming language of your choice.

• Each numeric variable and constant, whether used by name or literal value, counts as 1 point.
• Each basic operation, as defined above, counts as 1 point.
• Each definition of a custom function or method counts as 5 points.
• Each call of a custom function or method counts as 1 point.
• Imports and similar initializations required by the programming language are ignored.
• Neither reading the input value and returning or printing the output value nor eventual variables for storing their value are counted.
• The answer with the fewest points wins.
• TBD…

Example:

function CFAQEaster(year) { // Calendar FAQ
// 5 points for Div() function
var G, C, H, I, J, L // 6 points for variables
G = year % 19        // 2: 1 point for modulo, 1 point for 19
C = Div(year,100)    // 2: 1 point for function call, 1 point for 100
H = (C - Div(C,4) - Div(8*C+13,25) + 19*G + 15) % 30
// 16: 8 points for operations, 2 points for function calls, 6 points for additional numeric values
I = H - Div(H,28)*(1 - Div(29,H+1)*Div(21-G,11))
// 13: 5 points for operations, 3 points for function calls, 5 points for additional numeric values
J = (year + Div(year,4) + I + 2 - C + Div(C,4)) % 7
// 6 points for operations, 2 points for function calls, 2 points for additional numeric values
L = I - J            // 1 point for substraction
EasterMonth = 3 + Div(L+40,44)
// 6: 2 points for addition, 1 point for function call, 3 points for additional numeric values
EasterDay = L + 28 - 31*Div(EasterMonth,4)
// 6: 3 points for operations, 1 point for function call, 2 points for additional numeric values
return {Y:year, M:EasterMonth, D:EasterDay}
// 63 points in total
}


Contemporary example input: output

• 2001: 15
• 2002: 13
• 2003: 16
• 2004: 15
• 2005: 12
• 2006: 15
• 2007: 14
• 2008: 12
• 2009: 15
• 2010: 13
• 2011: 16
• 2012: 14
• 2013: 13
• 2014: 16
• 2015: 14
• 2016: 12
• 2017: 15
• 2018: 13
• 2019: 16
• 2020: 15
• 2021: 13

The return value must be correct for a complete cycle of input years, i.e. from 1 through 5700000, even though the original event that is celebrated did not occur before 30 (if ever at all) and the Gregorian Calendar was not used before late 1582, i.e. the proleptic Gregorian Calendar applies.

Resources

• I believe this challenge is better done as alorithm-golfing rather than counting characters or bytes. However, I'm not sure at all how to award a score. The rules above are very much up to bikeshedding. Jul 1 at 10:46
• The main problem with any kind of scoring like this is that many programming languages have very different set of built-in operations and features. How many points for using a mapping or reduction on an array? How many points for swapping two numbers on the stack? How many points for using the 1 command in Hexagony, which computes x>=0?x*10+1:x*10-1? A better way would be to fix the language and a very strict set of features available, like "use Python 3, only +-*/ operators on numbers are allowed". Jul 14 at 7:28
• A few suggestions: perhaps add the date tag, and say something like Output "WEEKDAY" if there are 5 dates, all from Monday-Friday, "WEEKEND" if there are two dates: Saturday and Sunday, and "ALLDAYS" if the input contains seven days all from Monday-Sunday.`
– user100690
Jun 28 at 12:46

Generate the shortest regex to match these but not those

• A possible short program just enumerates all the regexes. This might not be feasible, and you may not be able to score submissions at all... Jun 28 at 17:34
• @Trebor I don't quite understand what you mean by this. Jun 28 at 18:13
• If you just write a program and tests, one by one, all the regexes, and outputs the first one that works, this would be a valid program. But to give it a score, you would probably need days, if not years. Jun 29 at 8:06

Solve Fermat's Last Theorem with matrices

Fermat's Last Theorem states that there is no such triple of positive integers $$\(x, y, z)\$$ such that

$$x^n + y^n = z^n$$

for all integers $$\n > 2\$$. However, this conjecture does not hold for integer matrices:

\begin{align} & \left( \begin{matrix} 1 & 3 \\ 0 & 1 \end{matrix} \right)^3 + \left( \begin{matrix} -1 & 0 \\ 1 & -1 \end{matrix} \right)^3 \\ = & \left( \begin{matrix} 1 & 9 \\ 0 & 1 \end{matrix} \right) + \left( \begin{matrix} -1 & 0 \\ 3 & -1 \end{matrix} \right) \\ = & \left( \begin{matrix} 0 & 9 \\ 3 & 0 \end{matrix} \right) \\ = & \left( \begin{matrix} 0 & 3 \\ 1 & 0 \end{matrix} \right)^3 \\ \end{align}

You are to take two $$\k \times k\$$ integer matrices $$\A\$$ and $$\B\$$, and a positive integer $$\n \ge 2\$$, and output a $$\k \times k\$$ integer matrix $$\C\$$ such that

$$A^n + B^n = C^n$$

You may output any such $$\C\$$. You may also take $$\k\$$ as an input, and you may assume that $$\k \ge 2\$$

This is , so the shortest code in bytes wins

• Is it guaranteed that A, B, n are given so that such a C exists? Why not just make a challenge about taking the nth root of a given matrix (which is arguably the hardest part of the task)? Jul 14 at 6:54