389. Find the Difference 

1
2
3
4
5
6
7
8
9
10
11
class Solution {
    public char findTheDifference(String s, String t) {
        int res = 0;
        for (int i = 0; i < s.length(); i++) {
            res ^= s.charAt(i);
            res ^= t.charAt(i);
        }
        res ^= t.charAt(t.length() - 1);
        return (char) res;
    }
}

References

389. Find the Difference