input: Write a function to shuffle an array of integers randomly. Return the shuffled array.
  
  def shuffle(arr):
      random.shuffle(arr)
      return arr
  
  assert shuffle([1, 5, 9, 4, 2]) != [1, 5, 9, 4, 2]
  assert len(shuffle([1, 5, 9, 4, 2])) == 5
  assert shuffle([]) == []
output: def shuffle(arr):
      random.shuffle(arr)
      return arr