input: Write a function to find the largest three numbers from a given list. The function should return these three numbers in descending order.
  assert largest_three_numbers([1, 6, 3, 8, 7, 4])==[8, 7, 6]
  assert largest_three_numbers([5, 10, 3, 9, 2, 7])==[10, 9, 7]
  assert largest_three_numbers([4, 4, 4, 4])==[4, 4, 4]
  assert largest_three_numbers([1])==[1]
  assert largest_three_numbers([])==[]
output: def largest_three_numbers(nums):
      if len(nums) == 0:
          return []
      elif len(nums) == 1:
          return [nums[0]]
      elif len(nums) == 2:
          return sorted(nums, reverse=True)
      else:
          return sorted(nums, reverse=True)[:3]