Department::getHeadDepartmentId

protected function getHeadDepartmentId(int $curId, array $departmentTree): ?int
{
	foreach ($departmentTree as $headDepartmentId => $subDepartments)
	{
		foreach ($subDepartments as $subDepartmentId)
		{
			if ((int)$subDepartmentId == $curId)
			{
				return (int)$headDepartmentId;
			}
		}
	}

	return null;
}