QuickSort using Random Pivoting (original) (raw)
Last Updated : 14 Sep, 2023
In this article, we will discuss how to implement QuickSort using random pivoting. In QuickSort we first partition the array in place such that all elements to the left of the pivot element are smaller, while all elements to the right of the pivot are greater than the pivot. Then we recursively call the same procedure for left and right subarrays.
Unlike merge sort, we don't need to merge the two sorted arrays. Thus Quicksort requires lesser auxiliary space than Merge Sort, which is why it is often preferred to Merge Sort. Using a randomly generated pivot we can further improve the time complexity of QuickSort.
We have discussed at two popular methods for partitioning the arrays-Hoare's vs Lomuto partition scheme
It is advised that the reader has read that article or knows how to implement the QuickSort using either of the two partition schemes.
**Algorithm for random pivoting using Lomuto Partitioning
partition(arr[], lo, hi)
pivot = arr[hi]
i = lo // place for swapping
for j := lo to hi – 1 do
if arr[j] <= pivot then
swap arr[i] with arr[j]
i = i + 1
swap arr[i] with arr[hi]
return i
partition_r(arr[], lo, hi)
r = Random Number from lo to hi
Swap arr[r] and arr[hi]
return partition(arr, lo, hi)
quicksort(arr[], lo, hi)
if lo < hi
p = partition_r(arr, lo, hi)
quicksort(arr, lo , p-1)
quicksort(arr, p+1, hi)
**Implementation using Lomuto Partitioning:
C++ `
// C++ implementation QuickSort // using Lomuto's partition Scheme. #include #include <time.h> #include using namespace std;
// This function takes last element // as pivot, places // the pivot element at its correct // position in sorted array, and // places all smaller (smaller than pivot) // to left of pivot and all greater // elements to right of pivot int partition(int arr[], int low, int high) { // pivot int pivot = arr[high];
// Index of smaller element
int i = (low - 1);
for (int j = low; j <= high - 1; j++)
{
// If current element is smaller
// than or equal to pivot
if (arr[j] <= pivot) {
// increment index of
// smaller element
i++;
swap(arr[i], arr[j]);
}
}
swap(arr[i + 1], arr[high]);
return (i + 1);}
// Generates Random Pivot, swaps pivot with // end element and calls the partition function int partition_r(int arr[], int low, int high) { // Generate a random number in between // low .. high srand(time(NULL)); int random = low + rand() % (high - low);
// Swap A[random] with A[high]
swap(arr[random], arr[high]);
return partition(arr, low, high);}
/* The main function that implements QuickSort arr[] --> Array to be sorted, low --> Starting index, high --> Ending index */ void quickSort(int arr[], int low, int high) { if (low < high) {
/* pi is partitioning index,
arr[p] is now
at right place */
int pi = partition_r(arr, low, high);
// Separately sort elements before
// partition and after partition
quickSort(arr, low, pi - 1);
quickSort(arr, pi + 1, high);
}}
/* Function to print an array */ void printArray(int arr[], int size) { int i; for (i = 0; i < size; i++) cout<<arr[i]<<" "; }
// Driver Code int main() { int arr[] = { 10, 7, 8, 9, 1, 5 }; int n = sizeof(arr) / sizeof(arr[0]);
quickSort(arr, 0, n - 1);
printf("Sorted array: \n");
printArray(arr, n);
return 0;}
C
#include <stdio.h> #include <stdlib.h> #include <time.h>
int partition(int arr[], int low, int high) { int pivot = arr[low]; int i = low - 1, j = high + 1;
while (1) {
do {
i++;
} while (arr[i] < pivot);
do {
j--;
} while (arr[j] > pivot);
if (i >= j)
return j;
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}}
int partition_r(int arr[], int low, int high) { srand(time(0)); int random = low + rand() % (high - low);
int temp = arr[random];
arr[random] = arr[low];
arr[low] = temp;
return partition(arr, low, high);}
void quickSort(int arr[], int low, int high) { if (low < high) { int pi = partition_r(arr, low, high);
quickSort(arr, low, pi);
quickSort(arr, pi + 1, high);
}}
void printArray(int arr[], int n) { for (int i = 0; i < n; i++) printf("%d ", arr[i]); printf("\n"); }
int main() { int arr[] = { 10, 7, 8, 9, 1, 5 }; int n = sizeof(arr) / sizeof(arr[0]); quickSort(arr, 0, n - 1); printf("Sorted array: \n"); printArray(arr, n); return 0; }
Java
// Java program to illustrate // Randomised Quick Sort import java.util.*;
class RandomizedQsort
{
// This Function helps in calculating
// random numbers between low(inclusive)
// and high(inclusive)
static void random(int arr[],int low,int high)
{
Random rand= new Random();
int pivot = rand.nextInt(high-low)+low;
int temp1=arr[pivot];
arr[pivot]=arr[high];
arr[high]=temp1;
}
/* This function takes last element as pivot,
places the pivot element at its correct
position in sorted array, and places all
smaller (smaller than pivot) to left of
pivot and all greater elements to right
of pivot */
static int partition(int arr[], int low, int high)
{
// pivot is chosen randomly
random(arr,low,high);
int pivot = arr[high];
int i = (low-1); // index of smaller element
for (int j = low; j < high; j++)
{
// If current element is smaller than or
// equal to pivot
if (arr[j] < pivot)
{
i++;
// swap arr[i] and arr[j]
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
// swap arr[i+1] and arr[high] (or pivot)
int temp = arr[i+1];
arr[i+1] = arr[high];
arr[high] = temp;
return i+1;
}
/* The main function that implements QuickSort()
arr[] --> Array to be sorted,
low --> Starting index,
high --> Ending index */
static void sort(int arr[], int low, int high)
{
if (low < high)
{
/* pi is partitioning index, arr[pi] is
now at right place */
int pi = partition(arr, low, high);
// Recursively sort elements before
// partition and after partition
sort(arr, low, pi-1);
sort(arr, pi+1, high);
}
}
/* A utility function to print array of size n */
static void printArray(int arr[])
{
int n = arr.length;
for (int i = 0; i < n; ++i)
System.out.print(arr[i]+" ");
System.out.println();
}
// Driver Code
public static void main(String args[])
{
int arr[] = {10, 7, 8, 9, 1, 5};
int n = arr.length;
sort(arr, 0, n-1);
System.out.println("Sorted array");
printArray(arr);
} }
// This code is contributed by Ritika Gupta.
Python3
Python implementation QuickSort using
Lomuto's partition Scheme.
import random
''' The function which implements QuickSort. arr :- array to be sorted. start :- starting index of the array. stop :- ending index of the array. ''' def quicksort(arr, start , stop): if(start < stop):
# pivotindex is the index where
# the pivot lies in the array
pivotindex = partitionrand(arr,\
start, stop)
# At this stage the array is
# partially sorted around the pivot.
# Separately sorting the
# left half of the array and the
# right half of the array.
quicksort(arr , start , pivotindex-1)
quicksort(arr, pivotindex + 1, stop)This function generates random pivot,
swaps the first element with the pivot
and calls the partition function.
def partitionrand(arr , start, stop):
# Generating a random number between the
# starting index of the array and the
# ending index of the array.
randpivot = random.randrange(start, stop)
# Swapping the starting element of
# the array and the pivot
arr[start], arr[randpivot] = \
arr[randpivot], arr[start]
return partition(arr, start, stop)''' This function takes the first element as pivot, places the pivot element at the correct position in the sorted array. All the elements are re-arranged according to the pivot, the elements smaller than the pivot is places on the left and the elements greater than the pivot is placed to the right of pivot. ''' def partition(arr,start,stop): pivot = start # pivot
# a variable to memorize where the
i = start + 1
# partition in the array starts from.
for j in range(start + 1, stop + 1):
# if the current element is smaller
# or equal to pivot, shift it to the
# left side of the partition.
if arr[j] <= arr[pivot]:
arr[i] , arr[j] = arr[j] , arr[i]
i = i + 1
arr[pivot] , arr[i - 1] =\
arr[i - 1] , arr[pivot]
pivot = i - 1
return (pivot)Driver Code
if name == "main": array = [10, 7, 8, 9, 1, 5] quicksort(array, 0, len(array) - 1) print(array)
This code is contributed by soumyasaurav
C#
// C# program to illustrate // Randomised Quick sort using System; class RandomizedQsort {
/* This function takes last element as pivot, places the pivot element at its correct position in sorted array, and places all smaller (smaller than pivot) to left of pivot and all greater elements to right of pivot */ static int partition(int[] arr, int low, int high) {
// pivot is chosen randomly
random(arr, low, high);
int pivot = arr[high];
int i = (low-1); // index of smaller element
for (int j = low; j < high; j++)
{
// If current element is smaller than or
// equal to pivot
if (arr[j] < pivot)
{
i++;
// swap arr[i] and arr[j]
int tempp = arr[i];
arr[i] = arr[j];
arr[j] = tempp;
}
}
// swap arr[i+1] and arr[high] (or pivot)
int tempp2 = arr[i + 1];
arr[i + 1] = arr[high];
arr[high] = tempp2;
return i + 1; }
// This Function helps in calculating // random numbers between low(inclusive) // and high(inclusive) static int random(int[] arr, int low, int high) {
Random rand = new Random();
int pivot = rand.Next() % (high - low) + low;
int tempp1 = arr[pivot];
arr[pivot] = arr[high];
arr[high] = tempp1;
return partition(arr, low, high);}
/* The main function that implements Quicksort() arr[] --> Array to be sorted, low --> Starting index, high --> Ending index / static void sort(int[] arr, int low, int high) { if (low < high) { / pi is partitioning index, arr[pi] is now at right place */ int pi = partition(arr, low, high);
// Recursively sort elements before
// partition and after partition
sort(arr, low, pi - 1);
sort(arr, pi + 1, high);
} }
/* A utility function to print array of size n */ static void printArray(int[] arr) { int n = arr.Length; for (int i = 0; i < n; ++i) Console.Write(arr[i] + " "); Console.WriteLine(); }
// Driver Code static public void Main () { int[] arr = {10, 7, 8, 9, 1, 5}; int n = arr.Length;
sort(arr, 0, n-1);
Console.WriteLine("sorted array");
printArray(arr); } }
// This code is contributed by shubhamsingh10
JavaScript
// JavaScript implementation QuickSort using // Lomuto's partition Scheme.
/* The function which implements QuickSort. arr :- array to be sorted. start :- starting index of the array. stop :- ending index of the array. */ function quicksort(arr, start, stop) { if (start < stop) {
// pivotindex is the index where
// the pivot lies in the array
let pivotindex = partitionrand(arr, start, stop);
// At this stage the array is
// partially sorted around the pivot.
// Separately sorting the
// left half of the array and the
// right half of the array.
quicksort(arr, start, pivotindex - 1);
quicksort(arr, pivotindex + 1, stop);} }
// This function generates random pivot, // swaps the first element with the pivot // and calls the partition function. function partitionrand(arr, start, stop) {
// Generating a random number between the // starting index of the array and the // ending index of the array. let randpivot = Math.floor(Math.random() * (stop - start + 1)) + start;
// Swapping the starting element of // the array and the pivot [arr[start], arr[randpivot]] = [arr[randpivot], arr[start]]; return partition(arr, start, stop); }
/* This function takes the first element as pivot, places the pivot element at the correct position in the sorted array. All the elements are re-arranged according to the pivot, the elements smaller than the pivot is places on the left and the elements greater than the pivot is placed to the right of pivot. */ function partition(arr, start, stop) { let pivot = start; // pivot
// a variable to memorize where the let i = start + 1;
// partition in the array starts from. for (let j = start + 1; j <= stop; j++) {
// if the current element is smaller
// or equal to pivot, shift it to the
// left side of the partition.
if (arr[j] <= arr[pivot]) {
[arr[i], arr[j]] = [arr[j], arr[i]];
i++;
}} [arr[pivot], arr[i - 1]] = [arr[i - 1], arr[pivot]]; pivot = i - 1; return pivot; }
// Driver Code let array = [10, 7, 8, 9, 1, 5]; quicksort(array, 0, array.length - 1); console.log(array);
`
Output
Sorted array: 1 5 7 8 9 10
**Time Complexity: O(N*N)
**Auxiliary Space: O(N) // due to recursive call stack
**Algorithm for random pivoting using Hoare Partitioning
partition(arr[], lo, hi)
pivot = arr[lo]
i = lo - 1 // Initialize left index
j = hi + 1 // Initialize right index
while(True)
// Find a value in left side greater than pivot
do
i = i + 1
while arr[i] < pivot
// Find a value in right side smaller than pivot
do
j = j - 1
while arr[j] > pivot
if i >= j then
return j
else
swap arr[i] with arr[j]
end while
partition_r(arr[], lo, hi)
r = Random number from lo to hi
Swap arr[r] and arr[lo]
return partition(arr, lo, hi)
quicksort(arr[], lo, hi)
if lo < hi
p = partition_r(arr, lo, hi)
quicksort(arr, lo, p)
quicksort(arr, p+1, hi)
**Implementation using Hoare's Partitioning:
C++ `
// C++ implementation of QuickSort // using Hoare's partition scheme
#include #include using namespace std;
// This function takes last element as // pivot, places the pivot element at // its correct position in sorted // array, and places all smaller // (smaller than pivot) to left of pivot // and all greater elements to right int partition(int arr[], int low, int high) { int pivot = arr[low]; int i = low - 1, j = high + 1;
while (true) {
// Find leftmost element greater than
// or equal to pivot
do {
i++;
} while (arr[i] < pivot);
// Find rightmost element smaller than
// or equal to pivot
do {
j--;
} while (arr[j] > pivot);
// If two pointers met
if (i >= j)
return j;
swap(arr[i], arr[j]);
}}
// Generates Random Pivot, swaps pivot with // end element and calls the partition function // In Hoare partition the low element is selected // as first pivot int partition_r(int arr[], int low, int high) { // Generate a random number in between // low .. high srand(time(NULL)); int random = low + rand() % (high - low);
// Swap A[random] with A[high]
swap(arr[random], arr[low]);
return partition(arr, low, high);}
// The main function that implements QuickSort // arr[] --> Array to be sorted, // low --> Starting index, // high --> Ending index void quickSort(int arr[], int low, int high) { if (low < high) { // pi is partitioning index, // arr[p] is now at right place int pi = partition_r(arr, low, high);
// Separately sort elements before
// partition and after partition
quickSort(arr, low, pi);
quickSort(arr, pi + 1, high);
}}
// Function to print an array void printArray(int arr[], int n) { for (int i = 0; i < n; i++) printf("%d ", arr[i]); printf("\n"); }
// Driver Code int main() { int arr[] = { 10, 7, 8, 9, 1, 5 }; int n = sizeof(arr) / sizeof(arr[0]); quickSort(arr, 0, n - 1); printf("Sorted array: \n"); printArray(arr, n); return 0; }
Java
/* JAVA implementation of Randomize QuickSort using Hoare's Partition / import java.util.;
class GFG {
// swap function
static void swap(int[] arr, int i, int j)
{
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
/*
// partition function
This function takes array, low and high index,
swaps low with random index between low and high
then places all elements less than pivot in the left
of pivot and all elements greater than pivot to the
right of pivot
*/
static int partition(int[] arr, int low, int high)
{
// rIndex gives the random index between low and
// high (both inclusive)
int rIndex = (low) + (int)(Math.random() * (high - low + 1));
swap(arr, low, rIndex); // swap low with random index
int pivot = arr[low];
int i = low - 1, j = high + 1;
while (true) {
// increase i while elements are less than pivot
do {
i++;
} while (arr[i] < pivot);
// decrease j while elements are greater than pivot
do {
j--;
} while (arr[j] > pivot);
if (i >= j) // when both pointers meet
// that means elements are at their
// correct place for now
return j;
swap(arr, i, j);
// swap i and j, since both are not at their
// correct index
}
}
// recursive quick sort function
static void quickSort(int[] arr, int low, int high)
{
if (low < high) {
// find partition index
int p = partition(arr, low, high);
// sort before and after the pivot
quickSort(arr, low, p);
quickSort(arr, p + 1, high);
}
}
// Driver code
public static void main(String[] args)
{
int[] arr = { 10, 7, 8, 9, 1, 5 };
quickSort(arr, 0, arr.length - 1);
System.out.println("Sorted array : ");
System.out.print(Arrays.toString(arr));
}}
// This code is contributed by Anubhav Singh (singhanubhav)
Python3
Python implementation QuickSort using
Hoare's partition Scheme.
import random
''' The function which implements randomised QuickSort, using Haore's partition scheme. arr :- array to be sorted. start :- starting index of the array. stop :- ending index of the array. ''' def quicksort(arr, start, stop): if(start < stop):
# pivotindex is the index where
# the pivot lies in the array
pivotindex = partitionrand(arr,\
start, stop)
# At this stage the array is
# partially sorted around the pivot.
# separately sorting the left half of
# the array and the right
# half of the array.
quicksort(arr , start , pivotindex)
quicksort(arr, pivotindex + 1, stop)This function generates random pivot,
swaps the first element with the pivot
and calls the partition function.
def partitionrand(arr , start, stop):
# Generating a random number between
# the starting index of the array and
# the ending index of the array.
randpivot = random.randrange(start, stop)
# Swapping the starting element of
# the array and the pivot
arr[start], arr[randpivot] =\
arr[randpivot], arr[start]
return partition(arr, start, stop)''' This function takes the first element as pivot, places the pivot element at the correct position in the sorted array. All the elements are re-arranged according to the pivot, the elements smaller than the pivot is places on the left and the elements greater than the pivot is placed to the right of pivot. ''' def partition(arr,start,stop): pivot = start # pivot i = start - 1 j = stop + 1 while True: while True: i = i + 1 if arr[i] >= arr[pivot]: break while True: j = j - 1 if arr[j] <= arr[pivot]: break if i >= j: return j arr[i] , arr[j] = arr[j] , arr[i]
Driver Code
if name == "main": array = [10, 7, 8, 9, 1, 5] quicksort(array, 0, len(array) - 1) print(array)
This code is contributed by soumyasaurav
C#
// C# implementation of QuickSort // using Hoare's partition scheme using System;
public class GFG { // Driver Code
public static void Main()
{
int[] arr = { 10, 7, 8, 9, 1, 5 };
int n = arr.Length;
quickSort(arr, 0, n - 1);
Console.WriteLine("Sorted array: ");
printArray(arr, n);
}
// This function takes last element as
// pivot, places the pivot element at
// its correct position in sorted
// array, and places all smaller
// (smaller than pivot) to left of pivot
// and all greater elements to right
public static int partition(int[] arr, int low,
int high)
{
int pivot = arr[low];
int i = low - 1, j = high + 1;
// Find leftmost element greater than
// or equal to pivot
while (true) {
do {
i++;
} while (arr[i] < pivot);
// Find rightmost element smaller than
// or equal to pivot
do {
j--;
} while (arr[j] > pivot);
// If two pointers met
if (i >= j)
return j;
swap(arr, i, j);
}
}
// Generates Random Pivot, swaps pivot with
// end element and calls the partition function
// In Hoare partition the low element is selected
// as first pivot
public static int partition_r(int[] arr, int low,
int high)
{
// Generate a random number in between
// low .. high
Random rnd = new Random();
int random = low + rnd.Next(high - low);
// Swap A[random] with A[high]
swap(arr, random, low);
return partition(arr, low, high);
}
// The main function that implements QuickSort
// arr[] --> Array to be sorted,
// low --> Starting index,
// high --> Ending index
public static void quickSort(int[] arr, int low,
int high)
{
if (low < high) {
// pi is partitioning index,
// arr[p] is now at right place
int pi = partition_r(arr, low, high);
// Separately sort elements before
// partition and after partition
quickSort(arr, low, pi);
quickSort(arr, pi + 1, high);
}
}
// Function to print an array
public static void printArray(int[] arr, int n)
{
for (int i = 0; i < n; i++)
Console.Write("{0} ", arr[i]);
Console.Write("\n");
}
public static void swap(int[] arr, int i, int j)
{
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}}
JavaScript
// javascript implementation of QuickSort // using Hoare's partition scheme
// This function takes last element as // pivot, places the pivot element at // its correct position in sorted // array, and places all smaller // (smaller than pivot) to left of pivot // and all greater elements to right function partition(arr, low, high) { let pivot = arr[low]; let i = low - 1, j = high + 1;
while (true) {
// Find leftmost element greater than
// or equal to pivot
do {
i++;
} while (arr[i] < pivot);
// Find rightmost element smaller than
// or equal to pivot
do {
j--;
} while (arr[j] > pivot);
// If two pointers met
if (i >= j)
return j;
let temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}}
// Generates Random Pivot, swaps pivot with // end element and calls the partition function // In Hoare partition the low element is selected // as first pivot function partition_r(arr, low, high) { // Generate a random number in between // low .. high let random = low + Math.random() * (high - low);
// Swap A[random] with A[high]
let temp = arr[random];
arr[random] = arr[low];
arr[low] = arr[random];
return partition(arr, low, high);}
// The main function that implements QuickSort // arr[] --> Array to be sorted, // low --> Starting index, // high --> Ending index function quickSort(arr, low, high) { if (low < high) { // pi is partitioning index, // arr[p] is now at right place let pi = partition_r(arr, low, high);
// Separately sort elements before
// partition and after partition
quickSort(arr, low, pi);
quickSort(arr, pi + 1, high);
}}
// Function to print an array function printArray(arr, n) { for (let i = 0; i < n; i++) process.stdout.write(arr[i] + " "); }
// Driver Code
let arr = [ 10, 7, 8, 9, 1, 5 ]; let n = arr.length quickSort(arr, 0, n - 1); console.log("Sorted array: "); printArray(arr, n);
// The code is contributed by Nidhi goel.
`
Output
Sorted array: 1 5 7 8 9 10
**Time Complexity: O(N*N)
**Auxiliary Space: O(N) // due to recursive call stack
**Implementation using generateRandomPivot function :
Here is an implementation without using Hoare's and Lomuto partition scheme
**Implementation of QuickSort using random pivoting without partitioning:
C++ `
#include #include #include
using namespace std;
// Function to swap two elements void swap(int* a, int* b) { int temp = *a; *a = *b; *b = temp; }
// Function to generate a random pivot index int generateRandomPivot(int low, int high) { srand(time(NULL)); return low + rand() % (high - low + 1); }
// Function to perform QuickSort void quickSort(int arr[], int low, int high) { if (low < high) { int pivotIndex = generateRandomPivot(low, high); int pivotValue = arr[pivotIndex];
// Swap the pivot element with the last element
swap(&arr[pivotIndex], &arr[high]);
int i = low - 1;
for (int j = low; j < high; j++) {
if (arr[j] < pivotValue) {
i++;
swap(&arr[i], &arr[j]);
}
}
// Swap the pivot element back to its final position
swap(&arr[i+1], &arr[high]);
// Recursively sort the left and right subarrays
quickSort(arr, low, i);
quickSort(arr, i+2, high);
}}
int main() { int arr[] = {5, 2, 7, 3, 1, 6, 4, 8}; int n = sizeof(arr)/sizeof(arr[0]);
cout << "Original array: ";
for (int i = 0; i < n; i++) {
cout << arr[i] << " ";
}
quickSort(arr, 0, n-1);
cout << "\nSorted array: ";
for (int i = 0; i < n; i++) {
cout << arr[i] << " ";
}
return 0;}
Java
import java.util.Random;
public class QuickSort {
// Function to swap two elements in the array
static void swap(int[] arr, int i, int j) {
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
// Function to generate a random pivot index
static int generateRandomPivot(int low, int high) {
Random random = new Random();
return random.nextInt(high - low + 1) + low;
}
// Function to perform QuickSort
static void quickSort(int[] arr, int low, int high) {
if (low < high) {
int pivotIndex = generateRandomPivot(low, high);
int pivotValue = arr[pivotIndex];
// Swap the pivot element with the last element
swap(arr, pivotIndex, high);
int i = low - 1;
for (int j = low; j < high; j++) {
if (arr[j] < pivotValue) {
i++;
swap(arr, i, j);
}
}
// Swap the pivot element back to its final position
swap(arr, i + 1, high);
// Recursively sort the left and right subarrays
quickSort(arr, low, i);
quickSort(arr, i + 2, high);
}
}
// Driver code
public static void main(String[] args) {
int[] arr = {5, 2, 7, 3, 1, 6, 4, 8};
int n = arr.length;
System.out.print("Original array: ");
for (int num : arr) {
System.out.print(num + " ");
}
System.out.println();
quickSort(arr, 0, n - 1);
System.out.print("Sorted array: ");
for (int num : arr) {
System.out.print(num + " ");
}
System.out.println();
}}
Python3
import random
Function to swap two elements
def swap(arr, i, j): temp = arr[i] arr[i] = arr[j] arr[j] = temp
Function to generate a random pivot index
def generateRandomPivot(low, high): return random.randint(low, high)
Function to perform QuickSort
def quickSort(arr, low, high): if low < high: pivotIndex = generateRandomPivot(low, high) pivotValue = arr[pivotIndex]
# Swap the pivot element with the last element
swap(arr, pivotIndex, high)
i = low - 1
for j in range(low, high):
if arr[j] < pivotValue:
i += 1
swap(arr, i, j)
# Swap the pivot element back to its final position
swap(arr, i+1, high)
# Recursively sort the left and right subarrays
quickSort(arr, low, i)
quickSort(arr, i+2, high)Driver code
arr = [5, 2, 7, 3, 1, 6, 4, 8] n = len(arr)
print("Original array:", arr)
quickSort(arr, 0, n-1)
print("Sorted array:", arr)
C#
using System;
class Program { // Function to swap two elements static void Swap(int[] arr, int i, int j) { int temp = arr[i]; arr[i] = arr[j]; arr[j] = temp; }
// Function to generate a random pivot index static int GenerateRandomPivot(int low, int high) { Random random = new Random(); return low + random.Next(high - low + 1); }
// Function to perform QuickSort static void QuickSort(int[] arr, int low, int high) { if (low < high) { int pivotIndex = GenerateRandomPivot(low, high); int pivotValue = arr[pivotIndex];
// Swap the pivot element with the last element
Swap(arr, pivotIndex, high);
int i = low - 1;
for (int j = low; j < high; j++) {
if (arr[j] < pivotValue) {
i++;
Swap(arr, i, j);
}
}
// Swap the pivot element back to its final position
Swap(arr, i+1, high);
// Recursively sort the left and right subarrays
QuickSort(arr, low, i);
QuickSort(arr, i+2, high);
}}
static void Main() { int[] arr = {5, 2, 7, 3, 1, 6, 4, 8}; int n = arr.Length;
Console.Write("Original array: ");
for (int i = 0; i < n; i++) {
Console.Write(arr[i] + " ");
}
QuickSort(arr, 0, n-1);
Console.Write("\nSorted array: ");
for (int i = 0; i < n; i++) {
Console.Write(arr[i] + " ");
}} }
JavaScript
// Function to swap two elements function swap(arr, i, j) { let temp = arr[i]; arr[i] = arr[j]; arr[j] = temp; }
// Function to generate a random pivot index function generateRandomPivot(low, high) { return Math.floor(Math.random() * (high - low + 1)) + low; }
// Function to perform QuickSort function quickSort(arr, low, high) { if (low < high) { let pivotIndex = generateRandomPivot(low, high); let pivotValue = arr[pivotIndex];
// Swap the pivot element with the last element
swap(arr, pivotIndex, high);
let i = low - 1;
for (let j = low; j < high; j++) {
if (arr[j] < pivotValue) {
i++;
swap(arr, i, j);
}
}
// Swap the pivot element back to its final position
swap(arr, i + 1, high);
// Recursively sort the left and right subarrays
quickSort(arr, low, i);
quickSort(arr, i + 2, high);} }
// Driver code let arr = [5, 2, 7, 3, 1, 6, 4, 8]; let n = arr.length;
console.log("Original array: [" + arr.join(", ") + "]");
quickSort(arr, 0, n - 1);
console.log("Sorted array: [" + arr.join(", ") + "]");
`
Output
Original array: 5 2 7 3 1 6 4 8 Sorted array: 1 2 3 4 5 6 7 8
Analysis of Randomized Quick Sort
**Notes
- Using random pivoting we improve the expected or average time complexity to O (N log N). The Worst-Case complexity is still O ( N^2 ).