Single Number
Difficulty: Easy
Category: DSA
Topics: Array, Bit Manipulation
Asked at: Google, Amazon, Facebook, Microsoft
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 * 104`
- `-3 * 104 <= nums[i] <= 3 * 104`
- Each element in the array appears twice except for one element which appears only once.