1110

/**
 * 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) {}
 * };
 */
class Solution {
vector<TreeNode*> ans;
unordered_map<int, bool> m;
public:
    vector<TreeNode*> delNodes(TreeNode* root, vector<int>& to_delete) {
        for(int val: to_delete)
            m[val] = true;
        if(!m.count(root->val)) ans.push_back(root);
        dfs(root, NULL);
        return ans;
    }

    void dfs(TreeNode* curr, TreeNode* parent){
        if(!curr) return;
        dfs(curr->left, curr);
        dfs(curr->right, curr);

        // Delete the current node and add its left/right child to answer list.
        if(m.count(curr->val)){
            if(curr->left) ans.push_back(curr->left);
            if(curr->right) ans.push_back(curr->right);
            if(parent && parent->left == curr) parent->left = NULL;
            if(parent && parent->right == curr) parent->right = NULL;
            delete curr;
        }
    }
};