Find the Difference -- LeetCode

Given two strings s and t which consist of only lowercase letters.

String t is generated by random shuffling string s and then add one more letter at a random position.

Find the letter that was added in t.

Example:

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation:
'e' is the letter that was added.

思路：用map记录所有char出现的次数。复杂度O(N)。

 class Solution {
 public:
     char findTheDifference(string s, string t) {
         unordered_map<char, int> dict;
         for (int i = ; i < s.size(); i++)
             if (!dict.count(s[i])) dict.insert(make_pair(s[i], ));
             else dict[s[i]]++;
         for (int i = ; i < t.size(); i++)
             if (!dict.count(t[i]) || !dict[t[i]]) return t[i];
             else dict[t[i]]--;
         return '\0';
     }
 };