普通二叉树，每个节点的数值不相同。写一个函数，输入是树的根节点和要删除的节点的集合，删除某个节点意味着去除掉和这个节点的关联，剩下的都是子树，函数返回剩余子树数量。

input：root，｛1｝

output：2

input：root，｛1,,2,5｝

output：2

input：root，｛1,,2｝

output：3

input：root，｛4｝

output：3

input：root，｛4,9｝

output：2

程序还有点问题：

python
import copy
from typing import Set
class Node:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None
def getSubTree(root: Node, elements: Set, node_del=False) -> int:
"""
    if not elements or root is None:
        return 0
    if root.val in elements:
        elements = copy.deepcopy(elements)
        elements.remove(root.val)
        left_num = 1 + getSubTree(root.left, elements, True) if root.left is not None else 0
        right_num = 1 + getSubTree(root.right, elements, True) if root.right is not None else 0
        if node_del:
            return left_num + right_num - 1
        return left_num + right_num
    else:
        left_num = getSubTree(root.left, elements, False) if root.left is not None else 0
        right_num = getSubTree(root.right, elements, False) if root.right is not None else 0
        return left_num + right_num
        """
root = Node(1)
root.left = tree2 = Node(2)
root.right = tree3 = Node(3)
tree2.left = tree4 = Node(4)
tree2.right = tree5 = Node(5)
tree3.left = tree6 = Node(6)
tree3.right = tree7 = Node(7)
tree4.left = tree8 = Node(8)
tree4.right = tree9 = Node(9)
print(getSubTree(root, {1, 2, 5}))