> For the complete documentation index, see [llms.txt](https://algorithm.national-cat.me/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://algorithm.national-cat.me/leetcode/268.-missing-number.md).

# 268. Missing Number

```php
class Solution {

    /**
     * @param Integer[] $nums
     * @return Integer
     */
    function missingNumber($nums) {
        $count = count($nums);
        $total = ($count * $count + $count) / 2;
        return $total - array_sum($nums);   
    }
}
```