0001 template <typename T> BinTree<T> BinTree<T>::secede(BNP<T> x) { //子树分离
0002    FromParentTo(x) = nullptr; //切断来自父节点的指针
0003    if (x->parent) x->parent->updateHeightAbove(); //更新原祖先们的高度
0004    BinTree<T> S;  S._root = x;  x->parent = nullptr; //新树以x为根
0005    S._size = x->size();  _size -= S._size;  return S; //更新规模，返回子树
0006 } //secede