I did the same, but what if n = 2_147_483_647 ?

i forgot to change the panic!() to something else.. my retardness is too powerful

it panics anyway if the index is out of bound, so why repeat the

Yes i know, but i chose .copied() because i hate the aesthetics of the * operator

The first check should be first.len() != second.len(). Otherwise, the answer may be wrong.
E.g.,

first = "a"
second = "aa"

The answer should be None instead of 0.

It should panic, according to the description that's an invalid input.

If you enter 11 the code will panic. I don't think this is a "best practice."