Quick SortWe choose an element from the list, called the pivot. We'll use it to divide the list into two sub-lists.We reorder all the elements around the pivotThe ones with smaller value are placed before itAll the elements greater than the pivot after it.After this step, the pivot is in its final position. This is the important partition step.We apply the above steps recursively to both sub-lists on the left and right of the pivot. Quick Sort (Example)Consider the following array Arr[] = {5, 9, 4, 6, 5, 3}Let's suppose we pick 5 as the pivot for simplicityWe'll first put all elements less than 5 in the first position of the array: {3, 4, 5, 6, 5, 9}We'll then repeat it for the left sub-array {3,4}, taking 3 as the pivotThere are no elements less than 3We apply quicksort on the sub-array in the right of the pivot, i.e. {4}This sub-array consists of only one sorted elementWe continue with the right part of the original array, {6, 5, 9} until we get the final ordered array Quick Sort (Choosing Pivot)The crucial point in QuickSort is to choose the best pivot.○ The middle element is, of course, the best, as it would divide the list into two equal sub-lists.But finding the middle element from an unordered list is difficult and time-consuming, that is whywe take as pivot○ First element○ Last element○ Median○ Or any other random element

In Quicksort algorithm, choosing the pivot element in order to divide the list exactly two equal…

Answered: The crucial point in QuickSort is to…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

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Quick Sort

We choose an element from the list, called the pivot. We'll use it to divide the list into two sub-lists.
We reorder all the elements around the pivot
The ones with smaller value are placed before it
All the elements greater than the pivot after it.
After this step, the pivot is in its final position. This is the important partition step.
We apply the above steps recursively to both sub-lists on the left and right of the pivot.

Quick Sort (Example)

Consider the following array Arr[] = {5, 9, 4, 6, 5, 3}
Let's suppose we pick 5 as the pivot for simplicity
We'll first put all elements less than 5 in the first position of the array: {3, 4, 5, 6, 5, 9}
We'll then repeat it for the left sub-array {3,4}, taking 3 as the pivot
There are no elements less than 3
We apply quicksort on the sub-array in the right of the pivot, i.e. {4}
This sub-array consists of only one sorted element
We continue with the right part of the original array, {6, 5, 9} until we get the final ordered array

Quick Sort (Choosing Pivot)

The crucial point in QuickSort is to choose the best pivot.

○ The middle element is, of course, the best, as it would divide the list into two equal sub-lists.

But finding the middle element from an unordered list is difficult and time-consuming, that is why

we take as pivot

○ First element

○ Last element

○ Median

○ Or any other random element

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