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 };