QuickSort using Random Pivoting

// 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. 

/*
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)

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();
    }
}