class Solution {
  bool isIsomorphic(String s, String t) {
    Map<String, String> map = Map<String, String>();
    for (int i = 0; i < s.length; i++) {
      if (map.containsKey(s[i])) {
        if (map[s[i]] != t[i]) {
          return false;
        }
      } else if (map.containsValue(t[i])) {
        return false;
      } else {
        map[s[i]] = t[i];
      }
    }
    return true;
  }
}