后序的遞歸算法。
template <class T>
void recposttraverse(struct node<T>* Tree)
{
    if(Tree == NULL) return;
    recposttraverse(Tree->left);
    recposttraverse(Tree->right);
    visitnode(Tree);
}
后序的非遞歸算法要加入tag的實現。
template <class T>
void posttraverse(struct node<T>*tree)
{
    if(tree == NULL) return;
    MyStack<struct node<T> *> treestack;
    treestack.init(20);
    treestack.push(tree);
    struct node<T>* Item;
    while(treestack.gettop()!=0)
    {
        Item  = treestack.pop();
        if(Item&&Item->flag)//true is tree
        {
            Item->flag = false;
            treestack.push(Item);
            if(Item->right)
            treestack.push(Item->right);
            if(Item->left)
            treestack.push(Item->left);
        }
        else
        {
            visitnode(Item);
        }

    }


}