His solution is O(n) while yours is O(nlgn) :p

I think this needs a very simple test example to illustrate what the requirement is, until that's in place I'm going to pass on this one.

Am I missing something on Codewars, why aren't these tests shown? This leads to a deeply frustrating experience as we have to guess what the test might actually be, just saying check your code is not acceptable.

Might be nicer returning an option from this (Java version).

I'm not sure how this ended up as the top solution, two passes over the collection is sub optimal.

I think this solution is not quite correct when there are spaces or other non-alpha, non-digit characters.