Source: 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.

/**
* @param {number[]} nums
* @return {number}
*/
// XOR Approach
// Loop through the nums and continue to XOR the result with the current num
// Elements that appear twice will cancel out to 0 and the single number will be in final result
// O(N) time, O(1) space
var singleNumber = function(nums) {
 const result = nums.reduce((acc, current) => { return acc ^ current }, 0);
 return result;
};