input: Write a function to return the top 3 numbers from an array of integers in descending order. If the given array is empty, return an empty list.
  assert top_three([7, 13, 5, 8, 50, 11, 64, 48])==[64, 50, 48]
  assert top_three([1, 2, 3, 4, 5])==[5, 4, 3]
  assert top_three([10])==[10]
  assert top_three([])==[]
  assert top_three([15, 14, 13, 12, 11])==[15, 14, 13]
output: def top_three(arr):
      return sorted(arr, reverse=True)[:3]