input: Write a function to find the largest three numbers in a given list. If the list has fewer than three elements, return the largest numbers available. The function should return a list of the three largest numbers in descending order.
  
  assert largest_three([1, 6, 3, 8, 7, 4])==[8, 7, 6]
  assert largest_three([4, 5, 6])==[6, 5, 4]
  assert largest_three([9, 2])==[9, 2]
  assert largest_three([7, 7, 7, 7])==[7, 7, 7]
  assert largest_three([])==[]
output: def largest_three(nums):
      if len(nums) == 0:
          return []
      nums.sort(reverse=True)
      return nums[:3]