0001 template <typename T, typename V> void inorder1(BNP<T> x, V& visit) {
0002    Stack<BNP<T>> S;
0003    while (x || !S.empty()) { //只要x非nullptr，或S仍非空
0004       for ( ; x; x = x->lc) S.push(x); //藤上节点便自顶而下入栈
0005       visit((x = S.pop())->data);  x = x->rc; //取出并访问栈顶节点，再转向右子树
0006    } //while
0007 } //inorder1