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?

class Solution {
public:
    int singleNumber(int A[], int n) {
        int i;
        for (i = 1; i < n; i++) {
            A[0] ^= A[i];
        }
        return A[0];
    }
};