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.
Input: nums = [2,2,1] Output: 1
Input: nums = [4,1,2,1,2] Output: 4
Input: nums =  Output: 1
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.
class Solution: def singleNumber(self, nums: List[int]) -> int: result = 0 for num in nums: result ^= num return result