input: Write a python function to compare two strings and count the number of differing characters.
  assert compareStrings("kitten", "sitting") == 3
  assert compareStrings("flaw", "lawn") == 2
  assert compareStrings("intention", "execution") == 5
output: def compareStrings(s1, s2):
      return sum(1 for a, b in zip(s1, s2) if a != b) + abs(len(s1) - len(s2))