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.

132/155

思路：two hashmap一一对应字母。

public class Solution {    public boolean isIsomorphic(String s, String t) {        if(s.length()!=t.length()||s==null || t==null) return false;        Map
     
       res1=new HashMap<>();        Map
      
        res2=new HashMap<>();        for(int i=0;i<=s.length()-1;i++){            if(!res1.containsKey(s.charAt(i))){                res1.put(s.charAt(i),t.charAt(i));            }else{                if(res1.get(s.charAt(i))!=t.charAt(i))return false;            }            if(!res2.containsKey(t.charAt(i))){                res2.put(t.charAt(i),s.charAt(i));            }else{                if(res2.get(t.charAt(i))!=s.charAt(i))return false;            }        }        return true;    }}