QuickSort.java

public class QuickSort {
    //print arr
    public static void printArr(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; //to make place for  element smaller than pivot
       for(int j=si; j<ei; j++){
        if(arr[j] <= pivot){
            i++;
            //swap
            int temp = arr[j];
            arr[j] = arr[i];
            arr[i] = temp;
        }
       }
       i++;
       //swap
       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);
        printArr(arr);
    }
}