[leetcode 136] 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 == 1) {
            return A[0];
        }
        int res = A[0];
        for (int i = 1; i < n; i++) {
            res ^= A[i];
        }
        return res;
    }
};