class Solution {
public:
    char findTheDifference(string s, string t) {
        char ta[123] = { 0 };
        for (char c: t) {
            ta[c]++;
        }
        for (char c: s) {
            ta[c]--;
        }
        for (char i = 97; i < 123; i++) {
            if (ta[i] > 0) {
                return i;
            }
        }
        return 'a';
    }
};