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.

Note:

You may assume both s and t have the same length.

String类题目。 解题思路为记下各字符所在的位置，若两个string对应字符出现的位置不能对应，则不是isomorphic，返回false。 若字符只有ASCII码，则可用长度为128的固定数组，否则通用解法为采用hash map。

public class Solution {
    public boolean isIsomorphic(String s, String t) {
        if(s.length() != s.length()) return false;
        int[] sAddr = new int[128];
        int[] tAddr = new int[128];
        for(int i = 0; i < s.length(); i++) {
            if(sAddr[s.charAt(i)] != tAddr[t.charAt(i)]) {
                return false;
            }
            sAddr[s.charAt(i)] = i+1;
            tAddr[t.charAt(i)] = i+1;
        }
        return true;
    }
}