解决思路

Map

class Solution {
    public boolean isIsomorphic(String s, String t) {
        Map<Character,Character> map = new HashMap<>();
        if(s.length()!=t.length())return false;
        for(int i = 0;i<s.length();i++){
            char ss = s.charAt(i);
            char tt = t.charAt(i);
            if(map.containsKey(ss)){
                if(map.get(ss)!=tt)return false;
            }else{
                if(map.containsValue(tt))return false;
                map.put(ss,tt);
            }
 }              
        return true; 
        }
}