0001 template <typename T> Rank clean(BNP<T> x) { //析构子树x
0002    if (!x) return 0;
0003    Rank n = clean(x->lc) + clean(x->rc) + 1; //递归析构左、右子树
0004    delete x;  return n;
0005 } //clean
0006 
0007 template <typename T> Rank BinTree<T>::remove(BNP<T> x) { //删除子树x
0008    if (!x) return 0;
0009    FromParentTo(x) = nullptr; //切断来自父节点的引用
0010    if (x->parent) x->parent->updateHeightAbove(); //更新祖先们的高度
0011    Rank n = clean(x);  _size -= n;  return n; //析构子树x
0012 } //remove