input: Write a function to shuffle an array of integers using the random library's shuffle method. The function should return the shuffled array. If the array is empty, it should return the empty array.
  assert shuffle([1, 5, 9, 4, 2])!= [1, 5, 9, 4, 2]
  assert shuffle([])==[]
output: import random
  
  def shuffle(arr):
      if not arr:
          return arr
      random.shuffle(arr)
      return arr