# 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;
}
}
```