[LeetCode] 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.

题目很简单，也很容易想到方法，就是记录遍历s的每一个字母，并且记录s[i]到t[i]的映射，当发现与已有的映射不同时，说明无法同构，直接return false。但是这样只能保证从s到t的映射，不能保证从t到s的映射，所以交换s与t的位置再重来一遍上述的遍历就OK了。

class Solution {
public:
    bool isIsomorphic(string s, string t) {
        if (s.length() != t.length()) return false;
        map<char, char> mp;
        for (int i = 0; i < s.length(); ++i) {
            if (mp.find(s[i]) == mp.end()) mp[s[i]] = t[i];
            else if (mp[s[i]] != t[i]) return false;
        }
        mp.clear();
        for (int i = 0; i < s.length(); ++i) {
            if (mp.find(t[i]) == mp.end()) mp[t[i]] = s[i];
            else if (mp[t[i]] != s[i]) return false;
        }
        return true;
    }
};