<gh_stars>1-10
/*
Single Number
=============

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

Follow up: Could you implement a solution with a linear runtime complexity and without using extra memory?


Example 1:
Input: nums = [2,2,1]
Output: 1

Example 2:
Input: nums = [4,1,2,1,2]
Output: 4

Example 3:
Input: nums = [1]
Output: 1


Constraints:
1 <= nums.length <= 3 * 104
-3 * 104 <= nums[i] <= 3 * 104
Each element in the array appears twice except for one element which appears only once.

*/
class Solution
{
public:
  int singleNumber(vector<int> &nums)
  {
    int n = 0;
    for (int i = 0; i < nums.size(); ++i)
      n ^= nums[i];
    return n;
  }
};
