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.

思路：兩個hashMap分別存放s to t and t to s。如果不是一一對應，則返回.hashMap實現可以數組，也可以是hashMap。

public class Solution {
    public boolean isIsomorphic(String s, String t) {
        if(s==null||t==null||s.length()!=t.length()) return false;
        Map<Character, Character> sTot = new HashMap<>(26);
        Map<Character, Character> tTos = new HashMap<>(26);
        for(int i=0; i<s.length(); i++){
            if (sTot.containsKey(s.charAt(i))){
                if (sTot.get(s.charAt(i))!=t.charAt(i)) return false;
            }else{
                sTot.put(s.charAt(i),t.charAt(i));
            }
            if (tTos.containsKey(t.charAt(i))){
                if (tTos.get(t.charAt(i))!=s.charAt(i)) return false;
            }else{
                tTos.put(t.charAt(i),s.charAt(i));
            }
        }
        return true;
    }
}