CountOddRic BENE style

//BENE STYLE
public static int CountOddRic(BST T)
{
    BST last = null;
    var S = new Stack<BST>(); // stack dell'albero
    var RR = new Stack<int>(); // memorizzo il ret calcolato in preorder
    var RS = new Stack<int>(); // memorizzo il r_sx calcolato in inorder
    var ret = 0;

    while (S.Count > 0 || T != null)
        if (T != null)
        {
            // preorder
            ret = (T.Key % 2 == 1 ? T.Key : 0);
            RR.Push(ret);

            S.Push(T);
            T = T.Sx;
        }
        else
        {
            T = S.Peek();

            if (T.Dx != null && T.Dx != last)
            {
                // inorder
                if (T.Sx != null)
                    RS.Push(ret);

                T = T.Dx;
            }
            else
            {
                // postorder
                var r_sx = 0;
                var r_dx = 0;

                if (T.Sx != null && T.Dx == null)
                    r_sx = ret;
                else if (T.Sx != null && T.Dx != null)
                    r_sx = RS.Pop();

                if (T.Dx != null)
                    r_dx = ret;

                ret = RR.Pop();
                ret = ret + r_sx + r_dx;

                last = T;
                T = null;
                S.Pop();
            }
        }

    return ret;
}