Given two strings `s` and `t` of equal length, the Hamming distance
between `s` and `t`, denoted `d _{H}(s, t)`, is the
number of corresponding symbols that differ in

Example: The Hamming distance between these two strings below is 7. Mismatched symbols are colored red.

GAGCCTACTAACGGGAT CATCGTAATGACGGCCT

Given: Two DNA strings `s` and `t` of equal length (not exceeding 1 kbp).

Return: The Hamming distance `d _{H}(s, t)`.