Lowercase or Uppercase

Limits: 2s, 128 MB

You are given a string S consisting of lowercase English letters (a, b, c ….. z), uppercase English letters (A, B, C … Z) and digits (0, 1, 2 …. 9). You are allowed to change any element in any position of S with lowercase or uppercase English letters.

This is a companion discussion topic for the original entry at https://toph.co/p/lowercase-or-uppercase