quickSort.java

import java.io.*;
import java.util.*;

public class quickSort {
    // function to do the partition of an array
    public static int partition(int[] arr, int l, int h){
        int pivot = arr[l];
        int i = l;
        for(int j=l+1; j<=h; j++){
            if(arr[j] <= pivot){
                i = i + 1;
                // swap(arr[i], arr[j])
                int tem = arr[i];
                arr[i] = arr[j];
                arr[j] = tem;
            }
        }
        // swap (arr[l], arr[i])
        // to get the correct position of the pivot element
        int tem = arr[l];
        arr[l] = arr[i];
        arr[i] = tem;

        return i;
    }



    // function of the quicksort algorithm
    public static void quickSort(int[] arr, int l, int h){
        if(l < h){
            // 1. Divide the array into two subproblems
            int m = partition(arr, l, h);
            // 2. Conquer the subproblems via the recursion
            quickSort(arr, l, m-1);
            quickSort(arr, m+1, h);
            
        }
    }

    // function to display the array
    public static void printArr(int[] arr, int n){
        for(int i=0; i<n; i++){
            System.out.print(arr[i]+" ");
        }
        System.out.println(" ");
    }

     public static void main(String[] args){
        int[] arr = {50, 30, 70, 90, 10, 34, 89, 98, 13};
        int n = arr.length;

        System.out.println("Array before sorting is: ");
        printArr(arr, n);

        quickSort(arr, 0, n-1);

        System.out.println("Array after sorting is: ");
        printArr(arr, n);

    }
}