old 4 kyu -> now 6kyu

Your solution is O(N) + O(N) + O(N^2) in which the kata can be solved with an O(NLogN) algorithm. Read about how the step helps in deducing the output primes.

AFAIK, it's because i64 implements the trait Ord, which contains those methods.

That's because you dont need the parenthesis inside the brackets (character set)

Changed to more than 2 strings.

Great use of the range function. Creating a range function is O(n) right?

Yes, runtime on this solution will be n^2 since they are entering every number 1 by 1 and it's an N * N table which means N^2 items will need to be entered.

Other languages (e.g. python) have examples with three strings.
IMHO examples are correct and description should be "at least 3 strings"

Ah, it's in TypeScript. Not sure how to edit my previous comment.

Please mention the language you're talking about when reporting an issue (if the kata has more than one language available ofc).