QuickSort.java

/**  
 * 
 *   1. Quick Sort is an inplace sorting algorithm based on Divide and Conquer Approach.
 *   2. First a pivot element is choosen and partitions are made around the choosen pivot.
 *   3. Selection of pivot element decides the time complexity of algorithm.
 * 
 */

package Java.Sorting;

import java.util.*;
public class QuickSort {
    static void swap(int[] arr, int i, int j)
    {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }

    static int partition(int[] arr, int low, int high)
    {
        int pivot = arr[high];
        int i = (low - 1);

        for (int j = low; j <= high - 1; j++) {
            if (arr[j] < pivot) {
                i++;
                swap(arr, i, j);
            }
        }
        swap(arr, i + 1, high);
        return (i + 1);
    }

    static void quickSort(int[] arr, int low, int high)
    {
        if (low < high) {
            int pi = partition(arr, low, high);
            quickSort(arr, low, pi - 1);
            quickSort(arr, pi + 1, high);
        }
    }

    static void printArray(int[] arr, int size)
    {
        for (int i = 0; i < size; i++)
            System.out.print(arr[i] + " ");

        System.out.println();
    }

    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();

        int[] arr = new int[n];
        for(int i=0;i<n;i++){
            arr[i] = scan.nextInt();
        }

        System.out.println("Array before sorting");
        printArray(arr, n);
        System.out.println();

        quickSort(arr, 0, n - 1);

        System.out.println("Array after sorting ");
        printArray(arr, n);
        System.out.println();

        scan.close();
    }
}


// Contributor : Rishabh Srivastava 
// Github Link : https://github.com/RishabhSrivastava1423/