Isomorphic Strings

Given two strings s and t, determine if they are isomorphic.

Two strings are isomorphic if the characters in s can be replaced to get t.

All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character but a character may map to itself.

For example,
Given "egg", "add", return true.

Given "foo", "bar", return false.

Given "paper", "title", return true.

这题需要注意的地方是我们要从S到T 和T到S都检查一遍。

 public class Solution {
     public boolean isIsomorphic(String s, String t) {
         if (s.length() != t.length()) return false;

         Map<Character, Character> map = new HashMap<>();

         for (int i = ; i < s.length(); i++) {
             char chKey = s.charAt(i);
             char chValue = t.charAt(i);

             if(map.containsKey(chKey)) {
                 char value = map.get(chKey);
                 if (value != chValue) {
                     return false;
                 }
             } else {
                 map.put(chKey, chValue);
             }
         }

         map.clear();

         for (int i = ; i < s.length(); i++) {
             char chKey = t.charAt(i);
             char chValue = s.charAt(i);

             if(map.containsKey(chKey)) {
                 char value = map.get(chKey);
                 if (value != chValue) {
                     return false;
                 }
             } else {
                 map.put(chKey, chValue);
             }
         }

         return true;
     }
 }