input: Write a function to find the largest three numbers in a list. If the list has fewer than three numbers, return all the numbers in descending order. If the list is empty, return an empty list.
  assert largest_three_numbers([1, 6, 3, 8, 7, 4])==[6, 7, 8]
  assert largest_three_numbers([3, 5])==[3, 5]
  assert largest_three_numbers([4, 3, 1, 2])==[2, 3, 4]
  assert largest_three_numbers([3, 5, 4, 1, 2])==[3, 4, 5]
  assert largest_three_numbers([])==[]
output: def largest_three_numbers(lst):
      if not lst:
          return []
      sorted_lst = sorted(lst, reverse=True)
      return sorted_lst[:3]