Single Number

Problem

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.

Solution

Relies on that xor trick. Related.

class Solution {
    public int singleNumber(int[] nums) {
        var counter = 0;
        for (var n : nums) {
            counter ^= n;
        }
        return counter;
    }
}