I just kinda copy and pasted all the using; from visual studio code but I realise I could have just used System on its own now lol

loooool, this is definitely a problem that will require collections and multithreading

Thank you for checking and your comment. Will follow it for the next Kata :)

Mh, yes, unless you declare it as static somewhere?

If you want to be picky (and go downvote somewhere else), some engine might behave smarter than that, but JS on its own doesn't.

See, for example.

Also, declaring gcd inside the function will have you reallocate memory each time you call solution

Are you sure this is actually the case in JS?

Indentation :(

Also, declaring gcd inside the function will have you reallocate memory each time you call solution; and you might have read already how to make your code more concise, without redundant checks.

original thinking (wtf;)