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.

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

总结：用了hashmap

    public boolean isIsomorphic(String s, String t) {        int [] m = new int[512];        for(int i=0;i<s.length();i++){            if(m[s.charAt(i)] != m[t.charAt(i)+256]) return false;            m[s.charAt(i)] = m[t.charAt(i)+256] =i+1;        }        return true;    }

直接数组索引，归根结底看上一组出现的是不是同一个数字。还是不要用put