enumerate() returns a special generator from an iterable. In itself, it has O(1) runtime and does not split anything. If anything it is the iterator of str that is "splitting" (or better: iterating) the string into individual characters if you mean that. enumerate() just adds indices on top of that.

no, because letter is lowercase

that's clever but the time complexity is crying so therefore this should be mark higher as "clever" but not "Best Practice?.

don't understand why it is the first plase. this is solution - O(n**2), but it is 0(n)

couldn't you just return letter ? no need for return string[i]. The same output without enumerate

how??

Most people like small solutions rather than the efficient ones

It will be O(n^2) because of count, but good and fast solution overall.

to count upper and lower case letters as the same character. Otherwise using .count("A") wouldn't count in all lowercase "a" (as supposed to according to the instructions).

can anyone tell me why should use .lower() function?

because people tend to value short code over fast code, just the way it is

Nice one. I was using collections.Counter, but was struggling to find the solution.

Nice!!!! I'm glad I thought of the same solution!!! It feels sooo nice :')