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.

两种情况：1.s里第一次出现的数，t里不是第一次出现。2.s映射的字符与t相应位置上的字符不同。

public class Solution {

public boolean isIsomorphic(String s, String t) {
        
        if (s.length() != t.length()) {
            return false;
        }


        HashMap<Character, Character> hashMapS = new HashMap<Character, Character>();
        HashMap<Character, Character> hashMapT = new HashMap<Character, Character>();
        
        for (int i = 0; i < s.length(); i++) {
            if (hashMapS.containsKey(s.charAt(i))) {
                if (hashMapS.get(s.charAt(i)) != t.charAt(i)) {
                    return false;
                }
            } else {
                if (hashMapT.containsKey(t.charAt(i))) {
                    return false;
                }
                hashMapS.put(s.charAt(i), t.charAt(i));
                hashMapT.put(t.charAt(i), s.charAt(i));
            }
        }
        
        return true;
    }
}