input: Write a function to output the top 3 numbers from an array of integers.
  assert top_three([7, 13, 5, 8, 50, 11, 64, 48])==[64, 50, 48]
  assert top_three([3, 5, 10, 8, 2])==[10, 8, 5]
  assert top_three([9, 1, 7, 4, 15])==[15, 9, 7]
  assert top_three([1, 2, 3, 4, 5])==[5, 4, 3]
  assert top_three([0, 0, 0, 0, 0])==[0, 0, 0]
output: def top_three(arr):
      arr.sort(reverse=True)
      return arr[:3]