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.

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Example 1

Input: nums = [2, 2, 1]
Output: 1
Explanation: 1 appears only once while 2 appears twice.

Example 2

Input: nums = [4, 1, 2, 1, 2]
Output: 4
Explanation: 4 appears only once; 1 and 2 each appear twice.

Example 3

Input: nums = [1]
Output: 1
Explanation: 1 is the only element, so it appears once.

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Constraints

• 1 <= nums.length <= 3 * 10^4
• -3 * 10^4 <= nums[i] <= 3 * 10^4
• Each element in the array appears twice except for exactly one element which appears only once.