input: Write a function to find the largest three numbers in a list. The function should return a list of these three numbers. If the list has fewer than three numbers, return the list sorted in descending order.
  assert largest_three_numbers([1, 6, 3, 8, 7, 4])==[8, 7, 6]
  assert largest_three_numbers([9, 1, 3])==[9, 3, 1]
  assert largest_three_numbers([5, 2])==[5, 2]
  assert largest_three_numbers([10, 20, 30])==[30, 20, 10]
  assert largest_three_numbers([])==[]
output: def largest_three_numbers(nums):
      return sorted(nums, reverse=True)[:3]