input: Write a python function to implement quicksort algorithm.
  assert quick_sort([9,4,2,7,3,8,5,6]) == [2, 3, 4, 5, 6, 7, 8, 9]
  assert quick_sort([3,6,8,10,1,2,1]) == [1, 1, 2, 3, 6, 8, 10]
  assert quick_sort([1,4,3,9,7,5]) == [1, 3, 4, 5, 7, 9]
output: def quick_sort(arr):
      if len(arr) <= 1:
          return arr
      pivot = arr[len(arr) // 2]
      left = [x for x in arr if x < pivot]
      middle = [x for x in arr if x == pivot]
      right = [x for x in arr if x > pivot]
      return quick_sort(left) + middle + quick_sort(right)