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.

题目分析，两个字符串之间的一一映射关系，采用hash来处理，因为由两个字符串构成，因此必须构建两个hash映射表，保证两个字符串中字符之间的一一对应关系

public class Solution {

    public boolean isIsomorphic(String s, String t) {

        HashMap map1=new HashMap();  

        HashMap map2=new HashMap();  

        

        

        for(int i=0;i

        {

        

            if(map1.get(s.charAt(i))==null)

                map1.put(s.charAt(i),t.charAt(i));

            if(map2.get(t.charAt(i))==null)

                map2.put(t.charAt(i),s.charAt(i));    

            if(map1.get(s.charAt(i))!=t.charAt(i)||map2.get(t.charAt(i))!=s.charAt(i))

                    return false;

        }

        return true;

    }

}