input: Write a python function to determine if two strings are isomorphic.
  assert isIsomorphic("add", "egg") == True
  assert isIsomorphic("foo", "bar") == False
  assert isIsomorphic("paper", "title") == True
  assert isIsomorphic("abc", "def") == True
  assert isIsomorphic("ab", "aa") == False
output: def isIsomorphic(s1: str, s2: str) -> bool:
      if len(s1) != len(s2):
          return False
      
      mapping_s1_to_s2 = {}
      mapping_s2_to_s1 = {}
      
      for char_s1, char_s2 in zip(s1, s2):
          if (char_s1 in mapping_s1_to_s2 and mapping_s1_to_s2[char_s1] != char_s2) or \
             (char_s2 in mapping_s2_to_s1 and mapping_s2_to_s1[char_s2] != char_s1):
              return False
          mapping_s1_to_s2[char_s1] = char_s2
          mapping_s2_to_s1[char_s2] = char_s1
      
      return True