public static int partition(int arr[], int low, int high) {
        int pivot = arr[high];

        // index of smaller element
        int i = (low -1);

        for(int j = low; j < high; j++) {
            if (arr[j] <= pivot) {
                i++;
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }

        int temp = arr[i+1];
        arr[i+1] = arr[high];
        arr[high] = temp;
        return i + 1;
    }

     /*
     arr[]: array to be sorted
     low: start index
     high: end index
     */
    public static int 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);
        }
    }