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)。

 1 class Solution {
 2 public:
 3     char findTheDifference(string s, string t) {
 4         unordered_map<char, int> dict;
 5         for (int i = 0; i < s.size(); i++)
 6             if (!dict.count(s[i])) dict.insert(make_pair(s[i], 1));
 7             else dict[s[i]]++;
 8         for (int i = 0; i < t.size(); i++)
 9             if (!dict.count(t[i]) || !dict[t[i]]) return t[i];
10             else dict[t[i]]--;
11         return ‘\0‘;
12     }
13 };