Recursive QuickSort in C++ (memory-efficient)

qs.cpp

#include <iostream>
#include <cstdlib>
#include <cmath>
using namespace std;

void qs(int count, int ls[])
{
    int pivot, *hole;

    if (count < 1) return;

    pivot = ls[count / 2];
    hole = ls + count / 2;

    for (int i = count / 2 + 1; i < count; i++)
    {
        if (ls[i] < pivot)
        {
            *hole = ls[i];
            ls[i] = *(hole + 1);
            hole = hole + 1;
        }
    }

    for (int i = 0; i < count / 2; i++)
    {
        if (ls[i] >= pivot)
        {
            *hole = ls[i];
            ls[i] = *(hole - 1);
            hole = hole - 1;
        }
    }

    *hole = pivot;

    // Recurse into list of numbers smaller than pivot.
    qs(hole - ls, ls);
    // Recurse into list of numbers greater or equal than pivot.
    qs(ls + count - hole - 1, hole + 1);
}

int main()
{
    int count = pow(2, 30);
    int *ls;
    ls = (int*) malloc(sizeof(int) * count);
    for (int j = count, k = 0; j > 0; j--, k++)
    {
        ls[k] = j;
    }
    cout << "List created." << endl;
    qs(count, ls);
    cout << "First seven: " << ls[0];
    for (int i = 1; i < 7; i++) cout << ", " << ls[i];
    cout << endl;
    cout << "Last seven: " << ls[count - 7];
    for (int i = count - 6; i < count; i++) cout << ", " << ls[i];
    cout << endl;
    return 0;
}