题目：

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.

Note:

You may assume both s and t have the same length.

链接：  

2/24/2017

需要用2个hashmap，aa - > ab是不成立的

1 public class Solution { 2     public boolean isIsomorphic(String s, String t) { 3         if (s.length() != t.length()) return false; 4  5         HashMap
     
       h1 = new HashMap
      
       (); 6         HashMap
       
         h2 = new HashMap
        
         (); 7         char a, b; 8  9         for (int i = 0; i < s.length(); i++) {10             a = s.charAt(i);11             b = t.charAt(i);12             if (h1.containsKey(a)) {13                 if (h1.get(a) != b) return false;14                 h1.put(a, b);15             } else {16                 h1.put(a, b);17             }18             if (h2.containsKey(b)) {19                 if (h2.get(b) != a) return false;20             } else {21                 h2.put(b, a);22             }23         }24         return true;25 26     }27 }
        
       
      
     

别人的好算法可以用bitmap，留给二刷。