[LeetCode] Single Number

Given an array of integers, every element appears twice except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? 

a^a  = 0;

0^a = a;

a^b^a = a^a^b = 0^b = 0;

class Solution {
public:
    int singleNumber(int A[], int n) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int s = 0;
        for(int i = 0; i < n; i++) {
            s ^= A[i];
        }
        return s;
    }
};