注意特殊情况根节点被删除，就不放入res
没有解引用&，这个只是复制而已
删除结点用nullptr而不是NULL
这里用到的是后序遍历
左右子树分别讨论是否为空
写遍历别忘了回溯条件
/*** Definition for a binary tree node.* struct TreeNode {* int val;* TreeNode *left;* TreeNode *right;* TreeNode() : val(0), left(nullptr), right(nullptr) {}* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/void bitree(vector<TreeNode*>& res,TreeNode*& root,vector<int>& to_delete){if(root==NULL)return;bitree(res,root->left,to_delete);bitree(res,root->right,to_delete);auto it=find(to_delete.begin(),to_delete.end(),root->val);if(it!=to_delete.end()){if(root->right!=NULL){res.push_back(root->right);}if(root->left!=NULL){res.push_back(root->left);}root = nullptr;}}class Solution {public:vector<TreeNode*> delNodes(TreeNode* root, vector<int>& to_delete) {vector<TreeNode*>res;if(root){auto it=find(to_delete.begin(),to_delete.end(),root->val);if(it==to_delete.end()){res.push_back(root);}}bitree(res,root,to_delete);return res;}};