Input:s = "abcd"t = "abcde"Output:eExplanation:‘e‘ is the letter that was added.

 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 };