private static int[] quickSort(int[] a, int Lsel,int Rsel) {
    int pivot_loc;
    if (Lsel < Rsel) {
        pivot_loc = partition(a, Lsel, Rsel);
        quickSort(a, Lsel, pivot_loc);
        quickSort(a,pivot_loc+1,Rsel);
    }
    return a;
}
private static int partition(int[] a, int Lsel,int Rsel) {
    int pivot = a[Lsel];
    int lbound = Lsel;
    for (int i = Lsel + 1; i < Rsel; i++)
        if (a[i] < pivot) {
            swap(a, i, lbound);
            lbound++;
        }
    a[lbound] = pivot;
    return lbound;
}