input: Write a function to output the top 3 numbers from an array of integers. If the array has fewer than 3 numbers, return all of them sorted in descending order. If the array is empty, return an empty list.
  assert top_three([7, 13, 5, 8, 50, 11, 64, 48])==[64, 50, 48]
  assert top_three([3, 6, 1])==[6, 3, 1]
  assert top_three([9])==[9]
  assert top_three([])==[]
output: def top_three(arr):
      if not arr:
          return []
      return sorted(arr, reverse=True)[:3]