class Solution {
public:
    char findTheDifference(string &s, string &t) {
        int letterCount[30];

        for (int i = 0; i < 30; i++) {
            letterCount[i] = 0;
        }

        for (char e : s) {
            letterCount[e - 'a']++;
        }

        for (char e : t) {
            letterCount[e - 'a']--;
            if (letterCount[e - 'a'] < 0) {
                return e;
            }
        }

        return '\0';
    }
};