Single Lonely Number

In a given array of numbers, one element will show up once and the others will each show up twice. Can you find the number that only appears once in O(n) linear time? Bonus points if you can do it in O(1) space as well.

lonelyNumber([4, 4, 6, 1, 3, 1, 3])
// 6

lonelyNumber([3, 3, 9])
// 9

Constraints

• Length of the array <= 100,000
• The values of the array will be between -1,000,000,000 and 1,000,000,000

```js
function lonelyNumber(numbers) {
  // Fill in this method
  return numbers;
}

const result = lonelyNumber([4, 4, 6, 1, 3, 1, 3]);
console.log(result);
```