input: Write a python function to sort an array using quicksort.
  assert quickSort([10, 7, 8, 9, 1, 5])==[1, 5, 7, 8, 9, 10]
  assert quickSort([3, 6, 8, 10, 1, 2, 1])==[1, 1, 2, 3, 6, 8, 10]
  assert quickSort([1, 4, 3, 9, 7])==[1, 3, 4, 7, 9]
output: def quickSort(arr):
      if len(arr) <= 1:
          return arr
      else:
          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 quickSort(left) + middle + quickSort(right)