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

这道题使用异或即可，任何数和自己异或都是0，0和任何数异或都是这个数。

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int res = 0;
        for(auto it : nums){
            res ^= it;
        }
        return res;
    }
};