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