void preorder(node *T)
{
    stack<node*> s;
    while(T || !s.empty())
    {
        while(T)
        {
            printf("%d",T->data);
            s.push(T);
            T = T->lchild; 
        }

        if(!s.empty())
        {
            T = s.top();
            s.pop();
            T = T->rchild;
        }
    }
}

void inorder(node *T)
{
    stack<node*> s;
    while(T || !s.empty())
    {
        while(T)
        {
            s.push(T);
            T = T->lchild;
        }

        if(!s.empty())
        {
            T = s.top();
            s.pop();

            printf("%d",T->data);
            T = T->rchild;
        }
    }
}

void postorder(node *T)
{
    stack<node*> s;
    while(T || !s.empty())
    {
        while(T)
        {
            s.push(T);
            T = T->lchild;
        }

        if(!s.empty())
        {
            T = s.top();
            if(T->rchild && T->rchild->tag != 1)
            {
                T = T->rchild;
            }else
            {
                printf("%d",T->data);
                s.pop();
                T->tag = 1; //说明该节点被访问过 
                T = NULL;   //为了不进入循环，设置为NULL，代表以该节点为根节点的树遍历完 
            }
        }
    }
}