Given two stringssandt, determine if they are isomorphic.

Two strings are isomorphic if the characters inscan be replaced to gett.

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.

個人覺得挺有意思的一道題。首先要理解到底啥才叫lsomorphic strings。歸納出其的特點。

其實就是字母可以不相同，但是結構必須相同。就是說對于string s，其出現重復字母的index必須和string t，出現重復的字母的index相等而且數量也相同。

搞清楚這個就可以用if statement來寫判斷了。

代碼如下。~

public class Solution {    public boolean isIsomorphic(String s, String t) {        if(s.length()!=t.length()) return false;        HashMap<Character,Integer> smap=new HashMap<>();        HashMap<Character,Integer> tmap=new HashMap<>();        for(int i=0;i<s.length();i++){            if(!smap.containsKey(s.charAt(i))){                if(tmap.containsKey(t.charAt(i))){                    return false;                }            }else{                int index=smap.get(s.charAt(i));                if(!tmap.containsKey(t.charAt(i))||tmap.get(t.charAt(i))!=index){                    return false;                }            }            smap.put(s.charAt(i),i);            tmap.put(t.charAt(i),i);        }        return true;    }}