def quick_sort(arr, left_index, right_index):

if left_index < right_index:

partition_index = partition(arr, left_index, right_index)

quick_sort(arr, left_index, partition_index-1)

quick_sort(arr, partition_index+1, right_index)

def partition(arr, left_index, right_index):

pivot = arr[right_index]

partition_index = left_index

for i in range(left_index, right_index):

if arr[i] < pivot:

arr[i], arr[partition_index] = arr[partition_index], arr[i]

partition_index += 1

arr[partition_index], arr[right_index] = arr[right_index], arr[partition_index]

return partition_index

if __name__ == "__main__":

arr = [1,3,5,4,2,6,8,9,7,10,13,12,14,16,15,17,19,18]

quick_sort(arr, 0, len(arr)-1)

print(arr)