QuickSort.java

import java.util.*;
public class DivAndCon {
    public static void parray(int arr[]) {
        for(int i=0; i<arr.length;i++) {
            System.out.print(arr[i]+" ");

        }
        System.out.println();
    }
     public static void quicksort(int arr[],int si,int ei) {
        if(si>=ei) {
            return;
        }
        //last element
        int pIdx = partition(arr,si,ei);
        quicksort(arr,si,pIdx-1);//left
        quicksort(arr,pIdx+1,ei);//right
     }
     public static int partition(int arr[],int si,int ei) {
        int pivot = arr[ei];
        int i = si -1;
        for(int j=si;j<ei; j++) {
            if(arr[j] <= pivot) {
                i++;
                //swaping the values
                int temp=arr[j];
                arr[j]=arr[i];
                arr[i]= temp;
            }
        }
        i++;
        int temp = pivot;
        arr[ei] = arr[i];
        arr[i] = temp;
        return i;
     }

    public static void main(String args[]) {
        int arr[] = { 6,3,9,8,2,5};
        quicksort(arr,0,arr.length-1);
        parray(arr);
    }
}