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

LeetCode--Single Number