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