Problem

Given an integer array nums, every element appears exactly twice except for one element which appears only once.

Return the element that appears once.

You should aim for a solution with linear time complexity and constant extra space.

Input Format

• An integer array nums
• Each value appears twice except for one distinct value

Output Format

• Return the single element that appears only once

Constraints

• 1 <= nums.length
• Exactly one value appears once
• Every other value appears exactly twice
• Use integer values that fit in standard 32-bit signed integer ranges

Hints

• Think about an operation that cancels out equal values.
• Try to avoid using extra memory proportional to the array size.