Method quickSort

8_DivideAndConquer/QuickSort.java:9–18

(int arr[], int si, int ei)

    }

    public static void quickSort(int arr[], int si, int ei) {
        if(si >= ei) {
            return;
        }

        //pivot variable stores correct idx for pivot element
        int pIdx = partition(arr, si, ei);
        quickSort(arr, si, pIdx-1);
        quickSort(arr, pIdx+1, ei); 
    }

    public static int partition(int arr[], int si, int ei) {
        int pivot = arr[ei];