Day 2 Leet code series, today we will be picking the problem Single Number (https://leetcode.com/problems/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.

Example 1:

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

Example 2:

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

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int ans=nums[0];
        for(int i=1;i<nums.size();i++){
            ans = ans ^ nums[i];
        }
        return ans;
    }
};

Explaination:

1. We will use XOR method. Since we know that XOR or number with itself is 1.
2. So, at the end only the remaining number which does not has its pair will remain.