# 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

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

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

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

## Discussion

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

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

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

If you think one of your posts 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.

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

Get the Sandbox Viewer to view the sandbox more easily!

Create a C program that is less than 120 characters the produces the most ASM possible.

This limit does not include the def of main, or including headers. If a function is called the chars in the function count toward limit. The same goes for macros. The compiler used will be GCC 10.2 -O3 targeting x86-64.

The code conforms to these parameters and produces the most instructions wins.

I have a few questions regarding this. Is the character limit too limiting? Is the choice of compiler a good one? Is the optimization level being -O3 a good idea? Please share any other thoughts you have.

Thanks

• I don’t see a reason to limit the size of the program. You could score based on Assembly Instructions per Source Byte to encourage small code sizes without excluding a clever 121 byte solution. I also don’t think the rules around #include headers and counting the size of any functions called are clear (How many characters are in printf?). You could ban explicit #includes but allow implicit function declarations as long as the compiler accepts them. – water_ghosts Apr 5 at 2:17
• Should printf be 6 chars or should it be the size of the definition of the function printf? I'm not sure about this. – expr_champ2 Apr 5 at 3:57

# KotH: Assembly Anarchy

Draft. Just posting this so I don't forget I had this idea. Feel free to suggest improvements to the general idea here.

Basically, there would be a computer with memory and a processor. Programs would be submitted in a custom assembly language, and they would try to run a function (their flag) as many times as possible. They could try to interfere with other programs, by doing things like replacing the pointer to another bot's flag with their own, or preventing other bots from being run.

• I like the concept. It needs a lot of fleshing out, though. – jumbot Apr 9 at 13:42

# Poor Man's DRM

Write a program that only prints Welcome at the first execution and first execution only. All executions after the first execution should only print Where money.

Anything is allowed as long as the following condition is met: An execution ends after the program exits. So the second execution can only start after the first execution exits completely.

Reason for the condition: to prevent submissions that linger around in the memory and keep a runtime counter.

• any things that are disallowed? E.g. can a program write to its source file? – Wzl Apr 8 at 20:18
• @Wezl no, actually that's what I originally had in mind when writing this, but I decided to keep all the options open. -- edit for clarification: by "no", I meant it is allowed. – goodguy Apr 8 at 20:18
• @goodguy Nice challenge. You may want to look at Standard Loopholes and main article – math Apr 9 at 14:36

# Cooperative counting

• looks like a nice challenge – math Apr 9 at 11:11
• I can't wait to code a bot for this challenge! – math Apr 10 at 8:56
• @math patience :) – jumbot Apr 10 at 9:45

# Find the traitor cops-and-robbers (WIP)

In this challenge, the cops are the robbers/moles and the robbers are the cops/investigators.

## Cops

Cops will write a program that will output one of the following strings:

• "Hello World!"
• "Totally not evil stuff"
• "Good morning"
• "Innocent things"

However, when n specific characters are removed, where 0 < n < length of cop's program, the resulting program should output one of the following strings:

• "Bye World!"
• "Top secret stuff"
• "Evil things"
• "Horrible morning"

Cops will reveal the original program and n, but not the resulting program. They will also reveal the 2 strings that must be outputted by the original and transformed programs.

A cop's score is $$\\binom n r\$$, or $$\\frac{n!}{r!(n-r)!}\$$, where $$\r\$$ is the size of the cop's program and $$\n\$$ is the number of characters to be deleted. The lower the score, the better.

### Rules

• The original and transformed program may output in different ways, as long as the cop specifies what they are.
• The characters to be deleted do not have to be adjacent.

## Robbers

Robbers must find a way to make the cop's program output the chosen 2nd string by removing any n characters (not necessarily the same as the cop's).

## Example cop

Python, n = 1

a = ["Totally not evil stuff", "Hello World!"][01]
print(a)


The original string is "Hello World!", and the transformed program prints "Totally not evil stuff".

## Example robber

Python, cracks Foobar's answer

a = ["Totally not evil stuff", "Hello World!"][0]
print(a)


Deleting the 1 at the end of the first line prints the target string.

## Questions for Meta:

• Which original and transformed strings should I use?
• Is this a duplicate?
• This could be kind of difficult to write a cop for that doesn't just rely on someone brute forcing it – Redwolf Programs Apr 11 at 0:21
• @RedwolfPrograms Hmm, you're right. I guess just saying "pls don't brute force" wouldn't work. Maybe instead of a string, submissions could implement a mathematical function? You wouldn't be able to verify, say, cosine using just brute force. – user Apr 11 at 0:23
• That could be really cool actually. If you had a variety of ones like sqrt, tan, factorial, sum of proper divisors, and so on it would be a lot of fun. – Redwolf Programs Apr 11 at 0:30
• @RedwolfPrograms Only problem would be that there wouldn't be any more traitors to root out :( I made the challenge just for the title – user Apr 11 at 0:46

# Exchange of money in least notes

Suppose A and B are two good friends. A has borrowed $$\n\$$ dollar from B. Now B wants the money back from A and A is also ready to give it. But the problem is A has only $$\x\$$ dollar notes and B has $$\y\$$ dollar notes. They both want to keep the number of notes in exchange as low as possible.

As an example if $$\n=37\$$, $$\x=5\$$ and $$\y=2\$$, then the least amount of notes in exchange will be nine 5 dollar noted from A then four 2 dollar notes from B will make 37. This solution is found through brute forcing with a python program.

Here in the challenge your input will be values of $$\n, x, y\$$ and output should be the least of amount of notes as possible for A, B. A will give notes first and B later. Input and output seperator can be anything, no leading zeros in input numbers, no negative numbers in input. Standard loopholes apply and shortest code wins.

Test Cases

37 5 2 -> 9 4
89 3 8 -> 35 8
100 12 7 -> 13 8

• I'm almost certain there's a closed form solution to this, and if not one that's very close to closed form. – Redwolf Programs Apr 12 at 4:57
• Is it guaranteed that the given values of $n$, $x$ and $y$ lead to a valid solution? E.g. there's no solution for $n=21$, $x=6$, $y=4$. – Delfad0r Apr 12 at 8:22
• @Delfad0r input is guaranteed to valid – Wasif Apr 12 at 8:23

# A large number of stamps code-golfinteger-partitionsarithmetic

I have a large number of stamps of several different values. It's really annoying when I can't make a total exactly, so please write me some code to help me with this.

Your challenge is to make a function or program that takes an arbitrary number of integers as input and returns the largest integer that can't be made by adding several of those, repeated as many times as you like. For example, 22 can be made with 5 and 7 with $$\5+5+5+7\$$.

If there is no answer (there are always more you can't make), e.g. you are only given even numbers, you can return anything that's not a positive integer or error the program.

Input will never include 1.

# Testcases

5,7 => 23
3,5,6 => 7
6,9,12,15 => FALSE
45,91 => 3959


Note: for two values x and y the result is $$\xy-x-y\$$ - You may find this helpful.

# Scoring

This is , shortest wins!

# Meta

Is this clear?

I feel like just two arguments would result in tiny trivial programs using the specified formula.

How should this be tagged (aside from code-golf)?

Please can I have some more testcases?

• Related – pxeger Apr 13 at 10:37
• @pxeger But different. – A username Apr 13 at 10:46
• Is 1 promised not inputted? – l4m2 Apr 13 at 12:54
• I think [integer-partitions] would apply here, as would [arithmetic] – caird coinheringaahing Apr 13 at 15:03
• @l4m2 Yes, input won't be 1. – A username Apr 13 at 20:44
• @cairdcoinheringaahing probably – A username Apr 13 at 20:44
• I would suggest change falsy value to any values wont be ambiguous. For example, 0 should work here. While some languages (Lua for example) consider 0 as truthy. – tsh Apr 14 at 3:40
• @tsh Ok, anything that's not a positive integer. – A username Apr 14 at 4:31

# Basic Typescript Types

• suggested testcase: string | string, number & number – tsh Apr 14 at 10:15
• @tsh I just posted the question, thanks for the suggestion, I'll add the testcases there. – Etheryte Apr 14 at 10:17

# Matching to Homologous group

• 1. The underscore doesn't really seem necessary to me since there can't be any other syntax. 2. Can we assume the input will always be one of those categories? If not, add some test cases, and clarify the possible elements/other syntax that might be in the input. 3. Add classification tag? 4. Will you allow output as any 6 distinct values (not saying it has to be, but some challenges do allow this to remove the part of compressing some strings), or does it have to be those strings? If so, do they need to be capitalised exactly like that? – pxeger Apr 11 at 16:15
• @pxeger the input is guaranteed to be in 6 categories. Classification tag added. About the underscore i'll think later. And output needs to be exactly capitalized like in question. Thanks! – Wasif Apr 11 at 16:18
• Also maybe add some more test cases with larger numbers (more than 1 digit)? And clarify what integer syntax is allowed (areleading zeroes allowed, can the number be <2)? – pxeger Apr 11 at 16:21

# It seems $$\2^n\$$?

Let $$\a_0=1\$$ and $$\a_{i+1}=1+\sum_{j=0}^ia_i\$$, then $$\a_i=2^i\$$, which is no fun.

Now we reverse half of the value, $$\a_{i+1}=L(1+\sum_{j=0}^ia_i)\$$ for odd $$\i\$$, where $$\L\$$ reverse the number, e.g. 15=>51, 1230=>321.

Solve $$\a_i\$$. You can choose 1-index, or reverse each output(output $$\L(a_i)\$$).

First elements

1,2,4,8,16,23,55,11,121,242,484,869,1837,4763,8437,47861,64735,74921,204391,287804,696586,2713931,4107103,6024128,14238334,86667482,115144150,3882032,234170332,466043864,934384528,6509678681,8378447737,47459865761,64216761235,74225334821,202658857291,285417713504,690735428086,2716580741831,4098051598003,6006913016918,14203016212924,84852423060482,113258455486330,66279019615622,292795930588282,465671168195585,1051263029372149,8924478506252012,11027004564996310,2629992190045022,24684001320037642,48257004620086394,97625007260161678,653323025410052591,848573039930375947,4981570689706417961,6678716769567169855,1793343193533475331,15150776732667815041,28003653356435510303,58305206821771140385,77082245346314016611,193692658989856297381,267495217979713583783,654880535959426178545,907532588191701679031,2217293660110554036121,2422708011220237854344,6857295331441345926586,27135819628826609541731,40850410291709301394903,60898720681438502800718,142599541264857105590524,840181112417925280991582,1125380194947639492172630,625434898725989830670522,2876195288621268815015782,4651300367352427750932575,10403690944594965380964139,87282916703998198818370802,108090298593188129580299080,61895061952673681795081612,278075659139049940955679772,445953119188990872813151655,1002104437467090754724511199,8932209449051814394788024002,10936418323985995904237046400,829047480819917974663827812,22701884128791909783137920612,42214857266591838575286730454,87618625524175658141562571678,653341521382613153840152732571,828578772430964470123277875927,4581575556420498291684457517561,6238733101282427231931013269415,3883562026836445846520266477421


• 1) You should make it clear whether we need to print the $i$'th term, or the first $i$ terms or we can print the infinite sequence. Usually challenges like these allow all of these options. 2) Can you clarify what does "reverse each output" mean? So instead of $a_i$, the solutions can also print reverse of it? 3) There also needs to be a winning criterion. – Manish Kundu Apr 19 at 7:39

# Close neighbours stick together

• I felt like I'd done this at some point but couldn't find anything in my last 100 or so answers... I think it's a good easy level problem. – Jonah Apr 18 at 20:53

# Posted ;)

• So this is just abs(x-y), since I can just represent the days using integers? Doesn't seem very interesting – pxeger Apr 14 at 9:32
• I think restricting the input to being one of the 7 days (maybe in whatever consistent case answers want) would be a better version of this – caird coinheringaahing Apr 14 at 9:57
• Won't this be simple (x-y+7)%7? – tsh Apr 14 at 10:26

# Posted

• The idea seems to be compute an actually valid rule to replace the flawed schoolroom heuristic, and do so by means of a golfed algorithm. Given that goal, I think it would be easier to work with a word list of all correct words. Then the task is: "Your input will be a word from that list, either or unaltered or with the ie or ei transposed. Return true if unaltered, false if transposed" – Jonah Apr 18 at 18:33
• @Jonah I've edited the task with your suggestion. I hope this makes it less confusing. – dingledooper Apr 18 at 20:49
• Thanks. It's clear to me now and an interesting challenge. I suspect rather tough to golf well too. – Jonah Apr 18 at 20:52

# Plz Halp, Need Investors ASAP

• This might be a duplicate, but searching is going to be difficult because of how many ways you can describe the challenge. One thing that might make it interesting is giving each investor an amount of money they'll invest, then have the programs maximize the money invested (for example, by skipping three meetings with investors promising $1 and going to a single meeting with an investor who promises $10). – Redwolf Programs Apr 26 at 19:00
• The thing about that is that the algorithm gets a lot harder - I'm pretty sure you need DP to solve your variant. Also, I did spend quite a while looking for any duplicates and could not find any. – knosmos Apr 26 at 19:07

# Number to set - duplicate

• Dupe – caird coinheringaahing Apr 27 at 18:36
• aw rats, but thank you – Wzl Apr 27 at 18:37

# Decompress a Sparse Matrix (WIP)

The dual of this challenge

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

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

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

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

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


Or

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


Output will be a decompressed matrix/list of lists:

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


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

# Test cases

Input 1:

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


Output 1:

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


Input 2

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


Output 2:

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


Input 3:

[ ]
[ 0 0 0 0 ]
[ ]
3


Output 3:

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


Input 4:

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


Output 4:

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


Input 5:

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


Output 5:

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


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

# Scoring

This is a , fewest bytes wins.

• I'd suggest to at least briefly explain how the decompressing works in the post. The challenges should be self-contained as much as possible. – Bubbler Apr 22 at 23:55
• @bubbler, that's coming, but I need to figure out how to do that/explain it myself. I've left (WIP) on the question because of this. – Pureferret Apr 23 at 0:11
• @Pureferret I think it would be better to allow only nonzero integers instead of any real number. It'd be easier for most languages that way – user May 2 at 20:59
• @user I think it's more interesting seeing those languages work around those difficulties. Also the original challenge required them, so it I my makes sense this one does too. – Pureferret May 2 at 21:14
• @Pureferret I'm not sure many golfing languages support arbitrary precision floating point numbers. Would they be able to use strings, then? Edit: could you at least restrict it to rational numbers? Unlike Jon Skeet, most of us here don't know all the digits of pi :P – user May 2 at 21:17
• @user it needn't be arbitrary, just as long as it matches the test cases – Pureferret May 2 at 23:46
• You do need a objective winning criterion. See why here. Nice challenge though! Probably simplest to just make the criteria [code-golf]. Most [code-golf] challenges don't result in an accepted answer though, so you should be fine. – A username Apr 29 at 12:48
• @ausername Thanks for the feedback, I'll work on the winning criterion – EliteDaMyth Apr 29 at 12:51
• You don't need the last part, by the way. It's usually implied. – user Apr 29 at 19:30
• @user according the the comment above, the person said this needed a Winning Criterion thats the reason i added it. – EliteDaMyth Apr 29 at 19:55
• Sorry, I meant just the last sentence. Also, you don't need to make "Winning criterion" a separate header. – user Apr 29 at 20:05
• @user Alright, gonna remove it – EliteDaMyth Apr 29 at 20:08

# Self-Interpreter But Never Loops

I'm afraid that this might look too intimidating. Is there any way to improve it?

Ever since Gödel and Turing, it is widely assumed that a reasonable programming language that contains a self-interpreter can never be terminating. Here, I present a simple proof.

Suppose that, on the contrary, a total language has a self-interpreter eval(program, input) that accepts two natural numbers that encode programs and inputs, respectively. Then this function eval can be encoded as a natural number, since it is a program with two inputs. We define the function

evil(n) <- 1 + eval(n, n)


Then, since evil is a program, it can be encoded as a number EVIL. Therefore evil(EVIL) = 1 + eval(EVIL, EVIL). By the nature of eval it computes to 1 + evil(EVIL). But this is impossible, since no natural number is equal to one plus itself. Therefore, somewhere along the line of reasoning, one of the functions involved must loop indefinitely.

[On the other side, the program can also return something like StackOverflow or null, but that would render the self-interpreter incorrect, since the program that is being interpreted actually behaves differently.]

Of course, such a proof ignores a bunch of details -- in imperative languages, the function can change global variables; some nasty languages doesn't have anything like functions; some languages may not be able to define natural numbers, etc. But you get the idea. I quote C. T. McBride:

It's ironic, but not disastrous that lucifer, the evaluation function by which [...] angels [representing programs in a terminating subset of Haskell] bring their light, is himself an angel, but one who must be cast into Hell.

Now it's time for rebellion.

Challenge. Pick your favorite language (or a subset of it) that is terminating. Write a self-interpreter for it. The language must also contain (to eliminate trivial cases):

• Arithmetic for arbitrary precision integers.
• A program that always returns its input.
• Random-access lists.
• The encoding of programs must support random access. There must be a program that enumerates all legal programs up to size n, where n is the input.

What's happening here? Indeed, there are flaws in our reasoning above. A self-interpreter need not have its program encoded with natural numbers. And moreover, with an modestly elaborate type system, you can forbid the evil program to be well typed, as pointed out here. The linked paper already contains a program that fulfills the requirements of the challenge in the language $$\\mathrm F_\omega\$$ (arithmetic for integers and random-access lists are left as an exercise for the reader).

• so, a halting language plus an extra exec program? – l4m2 May 2 at 2:34
• @l4m2 Basically yes. – Trebor May 2 at 4:54

# Tips for golfing in Binary Lambda Calculus

• No, you don't need to post [tips] questions (especially these kind) in the Sandbox. Feel free to just post to main :) – caird coinheringaahing May 1 at 17:47
• Thanks for sandboxing this, though! It's nice to see new users using the Sandbox instead of directly posting to main - always better to be on the safe side. – user May 1 at 17:50
• @caird Wow! Thanks for the quick reply. Posted. – Andrew Li May 1 at 17:53
• I've edited this down to a stub now that it's been posted to save space – caird coinheringaahing May 1 at 17:55

# Base-ically god

• I've edited this down to a stub now that it's been posted to save space – caird coinheringaahing May 1 at 18:12

# Generate the ticks of a graph

• yes I need something like this. +1 because clearly specified and the gif demonstrates the different testcases well – lyxal May 1 at 5:30

# Assassin KoTH

## Description

Each bot is a point in the 2D plane. Each game, the list off bots is shuffled and each bot is a particular bot as their mark. This is done such that there is a cycle of assassins and targets.

Each bot's goal is to kill their mark and avoid their assassin. They can kill their target by getting within a certain distance to them. When they kill their target their new target is their target's assigned target. This continues until there are two bots left in the arena. Then each bot scores their kill count and the two remaining bots score their kill count plus a bonus.

## Sandbox

• What should the bonus for being one of the remaining bots be?

• Should the game take place on a grid instead of a 2D plane?

• Should there be a time limit?

• Is creating a bot accessible enough or is the game too complicated?

• Any other feedback?

• I think the bonus should be the number of bots in play. – StackMeter May 3 at 9:00
• @StackMeter Wouldn't that heavily bias the game in favour of camping? Getting kills and dying early should still be a viable strategy. – EnderShadow8 May 3 at 9:19
• Yeah, I see what happens what that in place: maybe you get double your score, so campers get 0 if they last to the end (0 * 2 is still 0). – StackMeter May 3 at 9:52
• @StackMeter Camping still needs to be a viable strategy though - more variety is better. – EnderShadow8 May 3 at 10:32
• 50*(kill/total bot)+survival bouns(5) or something similar. – okie May 10 at 1:41

# Sum multiplication carries

We have already counted how many carries are there in a sum. But what's their sum in a multiplication?

A carry is a digit that is transferred from one column of digits to another column of more significant digits.

When multiplying 15 and 3, a carry of 1 happens:

               1          1
15          15         15
×   3   ->  ×   3  ->  ×   3
-----       -----      -----
5         45


When multiplying 123 and 9, two carries of 2 happen:

               2         22         22
123         123        123        123
×   9   ->  ×   9  ->  ×   9  ->  ×   9
-----       -----      -----      -----
7         07       1107


When multiplying 23 and 52, a carry of 1 happens on the tens:

                                     1           1          1
23          23         23         23          23         23
×  52   ->  ×  52  ->  ×  52  ->  ×  52   ->  ×  52  ->  ×  52
-----       -----      -----      -----       -----      -----
6         46         46          46       1196
5         115


When multiplying 67 and 89, a carry of 6 happens on the ones and a carry of 5 on the tens.

               6          6          5           5          5
67          67         67         67          67         67
×  89   ->  ×  89  ->  ×  89  ->  ×  89   ->  ×  89  ->  ×  89
-----       -----      -----      -----       -----      -----
3        603        603         603       5963
6         536


When multiplying 3 and 2, no carry happens, as well as 5 and 2.

## Input

• Two positive integers.

## Output

• The sum of all carries that occurs when these two numbers are multiplied in base 10.

## Test cases

15, 3 -> 1
123, 9 -> 4
23, 52 -> 1
67, 89 -> 11
3, 2 -> 0
5, 2 -> 0
3125, 5 -> 3
257, 34 -> 7
21, 10 -> 0


Any suggestions? More test cases?

• Wont 23×52 cause 2 carries of 1 happened? As 2×5 also give a carry of 1? – tsh May 11 at 2:29

# Square chunk my matrix (Title suggestions welcome)

I have no context for this.

Your challenge is to write a function/program that takes a matrix m and a number n as input and:

Splits the matrix into nxn chunks

Replaces each chunk with the most common value in that chunk (In case of a tie, any of the tied values is fine).

Outputs the resulting matrix.

Example:

0 1 0 1
0 0 1 1
0 0 0 0
0 0 1 1,
2


Divide into chunks:

0 1|0 1
0 0|1 1
---+---
0 0|0 0
0 0|1 1


Take the most common value in each sub-matrix

0|1
-+-
0|0


So

0 1
0 0


is the result!

Note: You can assume that m's size will always be divisible by n.

# Testcases

0 1 2 1 2 1
2 2 1 0 2 2
2 1 2 0 1 0
0 0 1 0 3 2
3 0 2 0 3 1
1 0 3 2 0 1,
3 =>
2 1
0 0
(The 1 is a tie, any of 012 are fine)

0 1 2 1 2 1
2 2 1 0 2 2
2 1 2 0 1 0
0 0 1 0 3 2
3 0 2 0 3 1
1 0 3 2 0 1,
2 =>
2 1 2
0 0 3
0 2 1
(The 3 is a tie, any of 0123 are fine)


# Meta

• Title help needed
• Tags are - anything else?
• Any clarifications?
• Is this a dupe?
• Can I have some context?

# A general-purpose macrogenerator

Briefly: Implement Christopher Strachey's “General-purpose macrogenerator”.

## Background

In section 1.2 (Historical References) of the manual for GNU M4, an early macro processor is mentioned:

An important precursor of m4 was GPM; see C. Strachey, “A general purpose macrogenerator”, Computer Journal 8, 3 (1965), 225–41, http://dx.doi.org/10.1093/comjnl/8.3.225. GPM is also succinctly described in David Gries’s book Compiler Construction for Digital Computers, Wiley (1971). Strachey was a brilliant programmer: GPM fit into 250 machine instructions!

Your goal is to implement GPM, as described below, in the fewest bytes of source code possible.

## Overview

The version of GPM in this challenge is very close to that described in the original paper. GPM operates quite like m4, but there are some important differences. I assume that you already have an idea of what a macro is in general.

Input to GPM is a sequence of ASCII characters, which should be copied to the output verbatim, except that macros calls are expanded. Macro calls consist of a dollar sign $ followed by a name, followed by a comma ,, followed by a comma-separated list of arguments, followed by a semicolon ;. Here is an example of a macro call: $macro,x,yy,z;


In this case the name is macro, and there are three arguments (x, yy, and z). A macro call with no arguments is the name preceded by $ and followed by ;, as in $noarguments;.

Macro names consist of letters and/or digits. (So 1232 is a valid name.) There are no limitations on the length of a name.

When a macro call is encountered, it is replaced by the text currently associated with the name. (How text is associated with a name will be explained later; it is done by a macro named DEF.) This replacement text is also a sequence of characters suitable for input to GPM; in particular, it may itself include other macro calls. However, occurrences of ~1, ~2, ~3, etc. are replaced by the text of the corresponding argument given. The string ~0 is replaced by the macro's name.

Macro calls can be arguments, as in $macroA,$macroB,$macroC;,$macroD;;;. Dollar signs and semicolons must be balanced. Even the macro name in a macro call can be a macro call, so that $$x;; is valid. The name and arguments are evaluated from left to right before replacement begins. It is not a problem if more arguments are given than are used by the replacement text. After the call has been replaced, the resulting text is re-examined, in order to allow further expansion. For example, suppose that macro names a macro whose replacement text is ~1~1~2~2~3~3. Then the call given previously, namely macro,x,yy,z;, would be replaced by xxyyyyzz. Outside of a replacement text, the meaning of ~ followed by a digit is undefined. Your program need support only nine arguments, numbered ~1 to ~9. The usual treatment of a string of characters can be prevented by using the “quotes” < and >: Characters between < and > are not examined for macro calls. The evaluation of a quoted string is the string between the quotes but without the quotes. Quotes can nest. Quoted text need not be valid input. Thus <> and <;> are OK. It is not possible to quote a quoting character: <<> and <>> are invalid. However, <<><>> is fine; it evaluates to <><>. Here are some examples, mostly taken from Strachey's paper. Assume that the following definitions are active: Name Replacement text A A~1A B BA,X~1X;B APA P~1~1P Then we will have Input output A,C; ACA A,ACA; or A,A,C;; AACAA A,XDX; AXDXA B,D; BAXDXAB A,P; APA $$A,P;,Y; PYYP
Q<$A,C;>R Q$A,C;R
$A,<$A,X;>; A$A,X;A Q<$>R<;> Q$R; Q<<$A,C;>>R Q<$A,C;>R ## Macro definitions GPM maintains an environment of macro definitions, which is an ordered list of pairings of names and replacement texts. Entries are added and removed in a last-in-first-out manner. When it is time to expand a macro, the name is searched for in the environment, beginning with the most-recently-added definition and moving backwards. The first matching definition is the one used. After an expansion has finished, the environment returns to the state it was in before the expansion begun. Thus any macros defined in the process are forgotten. The built-in macro DEF can be used to modify the environment. It takes two arguments; the first is the name to define, and the second is the definition. The DEF macro is treated just as any macro is, except that the first argument, the name, is not evaluated. The effect of DEF is always to add a new definition to the environment, rather than to change an existing one. Here are some definitions for simple arithmetic: $DEF,Suc,<$1,2,3,4,5,6,7,8,9,10,$DEF,1,<~>~1;;>;
$DEF,Successor,<$~2,$DEF,~2,~1<,$Suc,>~2<;>;
$DEF,9,<$Suc,>~1<;,0>;;>;
$DEF,Sum,<$S,~1,~2,0,$DEF,S, <$~3,$DEF,~3,<$S,>$Successor,~1,~2; <,>$Suc,~3;<;>;
$DEF,>~3<,~1<,>~2;;>;;>;  The output of $Sum,3,4,2; is the sum of $$\34\$$ and $$\2\$$, expressed as 3,6.

Another basic macro, VAL, takes a name (which is not evaluated) as an argument and returns its unevaluated definition. Thus after defining $DEF,A,A;, $VAL,A; gives A (without evaluating it and getting into an infinite loop).

To change a definition, instead of (possibly temporarily) overriding it, the UPDATE macro is available. It is used like DEF, but changes the currently active definition of the name and does not add an entry. There must already be a definition before calling UPDATE.

The expansion of DEF and UPDATE is empty.

No limitations are placed on the number of characters making up a macro's replacement text. In the original program, the size of the new replacement text after an UPDATE call was restricted to being at most as long as the previous definition. You need not implement this restriction, but you also need not remove it.

## Implementation

Your program can get input from a file, from standard input, or from a string. Output can be to a file, to standard output, or to a string.

Whitespace (ASCII space, horizontal tab, vertical tab, line feed, carriage return) should be ignored but copied to the output. Thus $n a m e; is the same as $name. Strachey's implementation most likely did not differentiate between uppercase and lowercase letters, so you do not have to. The test does not depend on case differences.

Strachey's paper includes a detailed discussion of GPL's implementation, which you might find useful/interesting. It is not particularly easy to read. I don't think the 250-instruction machine code program has survived anywhere.

User tociyuki on GitHub has implemented the algorithm in Ruby and published it as a Gist, although UPDATE is not supported. I have not tested it.

Previously I have remarked that name length and replacement text size are not limited. This was true of Strachey's program but only to a certain extent. He enforced a limit on the total number of characters stored, but the length of any name or text was not fixed. You can do this as well, but your program must support storing at least 10000 characters, as he suggested.

Your program should allow at least 100 levels of expansion.

Don't bother with handling erroneous input; if given something invalid, your program can do anything.

## Test case

Input:

$DEF,Suc,<$1,2,3,4,5,6,7,8,9,10,$DEF,1,<~>~1;;>;$DEF,Successor,<$~2,$DEF,~2,~1<,$Suc,>~2<;>;$DEF,9,<$Suc,>~1<;,0>;;>;$DEF,Sum,<$S,~1,~2,0,$DEF,S,
<$~3,$DEF,~3,<$S,>$Successor,~1,~2;
<,>$Suc,~3;<;>;$DEF,>~3<,~1<,>~2;;>;;>;
$DEF,A,<A~1A>; /* First line of output$DEF,B,<B$A,X~1X;B>;$DEF,APA,<P~1~1P>;
This should be the second line of output.
The expansion of Suc is $VAL,Suc;. And I wrote that by saying: <The expansion of Suc is$VAL,Suc;>.
<<<Quote quote quote>>>
$A,C;$A,ACA; = $A,$A,C;;
$A,XDX;$B,D;
$A,P;$$A,P;,Y; Q<$A,C;>R
$A,<$A,X;>;
Q<$>R<;> Q<<$A,C;>>R
Q <  <  $A , C ; > > R */ #include <<stdio.h>> int main(void) { puts("Unaffected by the processor."); printf("Here's a sum: 34+2=%d%d.\n",$Sum,3,4,2;);

}


Expected output:

/* First line of output
This should be the second line of output.
The expansion of Suc is $1,2,3,4,5,6,7,8,9,10,$DEF,1,<~>~1;;.
And I wrote that by saying: The expansion of Suc is $VAL,Suc;. <<Quote quote quote>> ACA AACAA = AACAA AXDXA BAXDXAB APA PYYP Q$A,C;R
A$A,X;A Q$R;
Q<$A,C;>R Q<$A,C;>R */
#include <stdio.h>

int main(void)
{
puts("Unaffected by the processor.");
printf("Here's a sum: 34+2=%d%d.\n",3,6);
}


I believe that the computer for which Strachey's machine-code program was written used forty-eight-bit words (at least its predecessor did), so the mark to beat is 1500 bytes.

# Complete the Square (UNFINISHED)

Completing the square is (part of) a method for solving quadratic equations, which involves turning something like this:

$$ax^2+bx+c=0$$

Into something like this:

$$a(x-h)^2+k=0$$

I'll show how I was taught to do this. Take the quadratic $$\2x^2-8x+16\$$. First, divide out $$\a\$$:

$$2(x^2-4x+8)$$

Now, the goal is to add a number inside the parentheses which makes the quadratic the square of an $$\(x-n)\$$ term. In this case, adding $$\-4\$$ would result in $$\x^2-4x+4\$$, the square of $$\(x-4)\$$.

Importantly, you also need to subtract a number (outside the parentheses) in order to keep it the same overall. This results in:

$$2(x^2-4x+4)+8$$

Which can be simplified to:

$$2(x-2)^2+8$$

This can be used to solve quadratics, by rearranging that result a bit:

\begin{align}2(x-2)^2+8&=0\\2(x-2)^2&=-8\\(x-2)^2&=-4\\x-2&=\pm\sqrt{-4}\\x&=\pm\sqrt{-4}+2\\x&=2\pm2i\end{align}

Not sure what a good task would be for this but I already typed it all so I'm not discarding it :p

• I believe you can simply apply the quadratic formula and get $k=c-\frac{b^2}{4a}$ and $h=-\frac{b}{2a}$. Since you are just writing down how to get that formula step by step – tsh May 12 at 9:38
• @tsh That's the main reason I'm not sure what the task should be, since I don't want it to just be another "stick these values into a formula" challenge :p – Redwolf Programs May 12 at 13:29
• @RedwolfPrograms Not sure there's a good challenge buried in here. – Don Thousand May 12 at 20:05
• @DonThousand Yeah that's what I was worried about :/ – Redwolf Programs May 12 at 20:17
• Any feedback on either of my two recent challenges in Sandbox? – Don Thousand May 12 at 20:19

# Randomized Calculator code-golfarithmeticrandom

Imagine you want to make a random number generator. What if you want it more complex? For this challenge, you should write a program which:

• Takes 3 inputs:

• An integer $$\a\$$
• An integer $$\b\$$, such that $$\b \ge a\$$
• A string, $$\s\$$, detailed below, representing one of addition, subtraction, multiplication and division
• Generates two random integers, $$\x, y\$$, such that $$\a \le x\$$ and $$\b \ge y\$$. The integers should be uniformly random, and chosen independently

• And, outputs the result of applying $$\x\$$ and $$\y\$$ to the mathematical operation detailed by $$\s\$$

The following strings should be the expected ones to be used for $$\s\$$:

• Addition: a, +, plus, p, add
• Subtraction: s, -, subtract, minus
• Multiplication: m, *, x, times, t, multiply, ×, ·
• Division: d, /, divide, :, ÷

One example:

[4, 17, "times"] -> 35


as we generated $$\5\$$ and $$\7\$$ from the range $$\[4, 17]\$$, and multiplied them together.

Shortest code in bytes wins.

## Feedback

• Any more tags?
• Anything unclear?
• More rules to apply?
• I'd write "two" instead of "2" not to confuse it with the list item number. – Adám May 12 at 17:35
• I find it very unclear. Where did that times come from? – Adám May 12 at 17:42
• I've edited the spec a bit to make it clearer. Feel free to change anything I got wrong or that you dislike – caird coinheringaahing May 12 at 17:56
• @Adám x · y can be rewritten as "x times y". – r u even listening to me May 12 at 18:02
• No minus for subtraction? – Adám May 12 at 18:33
• @MatthewDaniels I have no idea why the fact x · y can be rewritten as "x times y" would cause times in the output. Anyway, with caird's rewrite, it isn't in the output any more. – Adám May 12 at 18:35
• Is it possible that $a≤0≤b$? – Adám May 12 at 18:36
• @Adám Yes. Both integers can be negative, yet $b$ shouldn't be negative if $a$ is positive. – r u even listening to me May 12 at 18:42
• @Adám No, the mathematical expression. Multiplication can mean times. For example, "6 multiplied by 10" is the same as "6 times 10". – r u even listening to me May 12 at 18:43
• @MatthewDaniels If only one of them can be negative at any one time, you should state so. Also, your statement that $a≤x$ and $b≥y$ needs clarification. Does this mean that both are unbounded to one side, i.e. $a≤x≤∞$ and $b≥y≥-∞$? – Adám May 12 at 18:45
• What happens if $b=0$ and the input requests division? – Adám May 12 at 18:46
• What happens if the output of division isn't an integer? With what precision should it be printed? – Command Master May 13 at 12:58
• Do we need to support all the strings for $s$ or may we choose one per category? – pajonk May 13 at 19:49

# Create word lightning ascii-artstringtree

Inspired by a Codingame challenge I tried (and failed at) recently.

Given a binary tree of words, say:

             HELLO
/     \
WORLD     EATING
/         /   \
ARCH     IDAHO   GUARD
/
DOOZY
/
ZEPPELIN
/    \
POWER   LIGHT

1. Take the root of the tree.
2. Print it in the South direction.
H
E
L
L
O

1. For each of the tree's children, given iteration index i:
1. Find the first common character of the child and the root.
2. The drawn root word will have to intersect the child at this point.
3. Draw the left node down to the left, and the right node down to the right.
   H
E
LA
LWT
O  I
R    N
L      G
D

1. Now, for each of the diagonal words' children, do the same, except always print downward.
   H
E
LA
LWT
AO  I
R   DN
LC   A G
D H   H U
O A
R
D

1. Go back to step3 and perform the steps again until the tree is complete.
   H
E
LA
LWT
AO  I
R   DN
LC   A G
D H   H U
O A
R
D
O
O
Z
YE
P
OP
W E
E  L
R   II
N G
H
T


## Clarifications

• No two child words will have the same first common letter.
• Words from different subtrees will never intersect.
• input will always be a valid binary tree.
• trees can be taken in any suitable and reasonable format for your language.

## Meta

• any possible duplicates?
• is there anything important to clarify that I left out?
• Is there anything I can simplify?
• Trees can be taken in different formats, right? – Wzl May 14 at 13:35
• yes, they can be taken in any suitable format. – Razetime May 14 at 13:47