205. 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.

一刷
很简单的思路，map。但是注意字母和字母之间只能是一一对应的关系，不能出现一对多。用set或者boolean array来解决都可以。

public class Solution {
    public boolean isIsomorphic(String s, String t) {
        if(s.length() == 0 && t.length() == 0) return true;
        if(s.length()!=t.length()) return false;
        Map<Character, Character> map = new HashMap<>();
        for(int i=0; i<s.length(); i++){
            char ss = s.charAt(i);
            char tt = t.charAt(i);
            if(map.containsKey(ss)){
                if(tt!=map.get(ss)) return false;
            }
            else{
                map.put(ss, tt);
            }
        }
        //in case that multiple character map to the same
        Set<Character> set = new HashSet<>();
        for(char ch : map.values()){
            if(set.contains(ch)) return false;
            else set.add(ch);
        }
        return true;
    }
}