input: Write a function to find the largest three numbers in a given list. The function should return a list containing the largest three numbers in descending order, or an empty list if the input list has fewer than three elements.
  
  def find_largest_three(nums):
      if len(nums) < 3:
          return []
      return sorted(nums, reverse=True)[:3]
  
  assert find_largest_three([1, 6, 3, 8, 7, 4])==[8, 7, 6]
  assert find_largest_three([1, 2])==[]
  assert find_largest_three([5, 10, 15, 20])==[20, 15, 10]
  assert find_largest_three([])==[]
  assert find_largest_three([11, 9, 7, 10, 12])==[12, 11, 10]
output: def find_largest_three(nums):
      if len(nums) < 3:
          return []
      return sorted(nums, reverse=True)[:3]