input: Write a python function to determine if two strings are isomorphic.
  assert isIsomorphic('egg', 'add') == True
  assert isIsomorphic('foo', 'bar') == False
  assert isIsomorphic('paper', 'title') == True
output: def isIsomorphic(s: str, t: str) -> bool:
      if len(s) != len(t):
          return False
      
      map_s_t = {}
      map_t_s = {}
      
      for char_s, char_t in zip(s, t):
          if char_s in map_s_t:
              if map_s_t[char_s] != char_t:
                  return False
          if char_t in map_t_s:
              if map_t_s[char_t] != char_s:
                  return False
                  
          map_s_t[char_s] = char_t
          map_t_s[char_t] = char_s
      
      return True