[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.

題目很簡單，也很容易想到方法，就是記錄遍歷s的每一個字母，並且記錄s[i]到t[i]的映射，當發現與已有的映射不同時，說明無法同構，直接return false。但是這樣只能保證從s到t的映射，不能保證從t到s的映射，所以交換s與t的位置再重來一遍上述的遍歷就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;
    }
};