not good. summing twice.

Unfortunely this is not a good solution, it's easy to implement, that's true but it's very slow. I tested it on a list of length 80 and k=6 and it took 188.6s whereas my solution took 1.77s

Never knew about this module, very convinient though lol

Why is the parallel one so complex?

I should use more builtin functions. Thanks

fyi ya can do (1..=n) instead (1..n + 1) to include the end of the range

This solution is going to be invalidated because the kata will be changed to use more suited unsigned types. I let you know so you may want to submit a new mended version.

Adding comments to describe applied math to a "fundamentals" "7 kyu" kata may increase votes on it.
After checking it out: exponents from prime factors?

try: validate_hello('halloween')

clever i could simplify my code :(. Didnt know that you can use x in y to find substring x in string y...

Great solution

holy crap this is the first time the top solution on a kata matches exactly what i did

This warning just indicates you stated as mutable a variable your code cannot mute.

Well, this is kinda a duh moment for me... I did an iteration version which is wildly unnecessary, if you see this one. If anyone is still wondering how it works, it uses integer division to round down to the nearest whole number before multiplying by the divisor to get the complement.