input: Write a function to output the top 3 numbers from an array of integers. If the given array has less than 3 numbers, then return the numbers 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, 13]
  assert top_three([1, 2])==[2, 1]
  assert top_three([])==[]
output: def top_three(arr):
      if not arr:
          return []
      return sorted(arr, reverse=True)[:3]