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 sorted in descending order. If the list is empty, return an empty list.
  
  assert largest_three([1, 6, 3, 8, 7, 4])==[6, 7, 8]
  assert largest_three([4, 5])==[4, 5]
  assert largest_three([10, 20, 30, 40])==[20, 30, 40]
  assert largest_three([])==[]
output: def largest_three(nums):
      if not nums:
          return []
      nums.sort(reverse=True)
      return nums[:3]