## Question

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

**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.

## Python Solution

class Solution: def singleNumber(self, nums: List[int]) -> int: return sum(set(nums)) * 2 - sum(nums)