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#Author: OMKAR PATHAK

#This program illustrates an example of quick sort

# Quicksort works by selecting an element called a pivot and splitting

# the array around that pivot such that all the elements in, say, the

# left sub-array are less than pivot and all the elements in the right

# sub-array are greater than pivot. The splitting continues until the

# array can no longer be broken into pieces. That's it. Quicksort is

# done.

# Best = Average = O(nlog(n)); Worst = O(n^2

import time

def quickSort(myList, start, end):

if start < end:

# partition the list

pivot = partition(myList, start, end)

# sort both halves

quickSort(myList, start, pivot-1)

quickSort(myList, pivot+1, end)

return myList

def partition(myList, start, end):

pivot = myList[start]

left = start+1

right = end

done = False

while not done:

while left <= right and myList[left] <= pivot:

left = left + 1

while myList[right] >= pivot and right >=left:

right = right -1

if right < left:

done= True

else:

# swap places

temp=myList[left]

myList[left]=myList[right]

myList[right]=temp

# swap start with myList[right]

temp=myList[start]

myList[start]=myList[right]

myList[right]=temp

return right

# A more efficient solution

def quicksortBetter(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 quicksortBetter(left) + middle + quicksortBetter(right)

if __name__ == '__main__':

List = [3, 4, 2, 6, 5, 7, 1, 9]

start = time.time()

print('Sorted List:',quickSort(List, 0, len(List) - 1))

stop = time.time()

print('Time Required:', (stop - start))

start = time.time()

print('Sorted List:', quicksortBetter(List))

stop = time.time()

print('Time Required:', (stop - start))