[Algorithm] 136. Single Number

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

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

Example 1:

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

Example 2:

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

var singleNumber = function(nums) {
    let res = 0;
    for (let i = 0; i < nums.length; i++) {
        res = res ^ nums[i]
    }
    return res;
};

It uses XOR: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators#Bitwise_XOR

For example, 4 ^ 2

4: 0100

2: 0010

XOR

   0110 => 6

But 

2: 0010

2: 0010

XOR

   0000 => 0