recursive backtrack knapsack in keep array

private static void ChooseBest(int[,] keep, int i, int j)
{
    if (i <= 0 || j < 0)
    {
        return;
    }

    if (keep[i,j] == 1)
    {
        bestProducts.Add(products[i - 1]);
        j = j - products[i - 1].Weight;
        i--;
    }
    else
    {
        i--;
    }

    ChooseBest(keep, i, j);
}