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