// Time Complexity: O(n) where n is t.size() + s.size()
// Memory Complexity: O(1)
class Solution {
public:
    char findTheDifference(string s, string t) {
        vector<int> counters(256, 0);

        assert(t.size() - s.size() == 1);

        for (auto c : t) {
            counters[c - 'a']++;
        }
        for (auto c : s) {
            counters[c - 'a']--;
        }
        for (int i = 0; i < 256; i++) {
            if (counters[i] > 0) {
                return 'a' + i;
            }
        }
        assert(false);
    }
};