Given a non-empty 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?

Example 1:

Input: [2,2,1]
Output: 1

Example 2:

Input: [4,1,2,1,2]
Output: 4

// OJ: https://leetcode.com/problems/single-number/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int ans = 0;
        for (int n : nums) ans ^= n;
        return ans;
    }
};