1110. Delete Nodes And Return Forest.cpp

// 1110. Delete Nodes And Return Forest
// Solved
// Medium
// Topics
// Companies
// Given the root of a binary tree, each node in the tree has a distinct value.

// After deleting all nodes with a value in to_delete, we are left with a forest (a disjoint union of trees).

// Return the roots of the trees in the remaining forest. You may return the result in any order.

 

// Example 1:


// Input: root = [1,2,3,4,5,6,7], to_delete = [3,5]
// Output: [[1,2,null,4],[6],[7]]
// Example 2:

// Input: root = [1,2,4,null,3], to_delete = [3]
// Output: [[1,2,4]]
 

// Constraints:

// The number of nodes in the given tree is at most 1000.
// Each node has a distinct value between 1 and 1000.
// to_delete.length <= 1000
// to_delete contains distinct values between 1 and 1000.

/**
 * 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 {
public:
    vector<TreeNode*> delNodes(TreeNode* root, vector<int>& to_delete) {
        vector<TreeNode*> rst;
        unordered_set<int> removeSet(to_delete.begin(), to_delete.end());

        root = dfs(root, removeSet, rst);
        if (root) rst.push_back(root);
        return rst;
    }


    TreeNode* dfs(TreeNode* root, unordered_set<int>& removeSet, vector<TreeNode*>& rst){
        if (root==nullptr) return nullptr;
        auto leftNode = dfs(root->left, removeSet, rst);
        auto rightNode = dfs(root->right, removeSet, rst);

        root->left = leftNode;
        root->right = rightNode;

        if (removeSet.count(root->val)){
            if (root->left) rst.push_back(root->left);
            if (root->right) rst.push_back(root->right);
            delete root;
            return nullptr;
        }
        return root;
    }
};