136. Single Number

Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.

You must implement a solution with a linear runtime complexity and use only constant extra space.

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