Single Number (XOR Bit Manipulation)

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 `O(n)` and use only constant extra space `O(1)`. ### Constraints - `1 <= nums.length <= 3 * 10^4` - `-3 * 10^4 <= nums[i] <= 3 * 10^4` - Each element appears twice except for one which appears once. ### Input Format A single line containing space-separated integers representing the array `nums`. ### Output Format Print the single unique integer.