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 ans=A[0];
        for(int i=1;i<n;i++) {
            ans = ans^A[i];
        }
        return ans;
    }
};