main.cpp

// Source: https://leetcode.com/problems/single-number
// Title: Single Number
// Difficulty: Easy
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 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 useonly constant extra space.
//
// **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 * 10^4`
// - `-3 * 10^4 <= nums[i] <= 3 * 10^4`
// - Each element in the array appears twice except for one element which appears only once.
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

#include <vector>

using namespace std;

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