<p>Given the <code>root</code> of a binary tree, each node in the tree has a distinct value.</p>

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

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

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2019/07/01/screen-shot-2019-07-01-at-53836-pm.png" style="width: 237px; height: 150px;" />
<pre>
<strong>Input:</strong> root = [1,2,3,4,5,6,7], to_delete = [3,5]
<strong>Output:</strong> [[1,2,null,4],[6],[7]]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> root = [1,2,4,null,3], to_delete = [3]
<strong>Output:</strong> [[1,2,4]]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

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

class Solution {
private:
    void traverse(TreeNode* root, queue<TreeNode*>* nodes, unordered_set<int> delete_set) {
        if(root == nullptr)
            return;

        if(root->left) {
            if(find(delete_set.begin(), delete_set.end(), root->left->val) != delete_set.end()) {
                if(root->left->left)
                    nodes->push(root->left->left);
                if(root->left->right)
                    nodes->push(root->left->right);
                root->left = nullptr;
            }
        }
        if(root->right) {
            if(find(delete_set.begin(), delete_set.end(), root->right->val) != delete_set.end()) {
                if(root->right->left)
                    nodes->push(root->right->left);
                if(root->right->right)
                    nodes->push(root->right->right);
                root->right = nullptr;
            }  
        }
        traverse(root->left, nodes, delete_set);
        traverse(root->right, nodes, delete_set);    
        return;
    }

public:
    vector<TreeNode*> delNodes(TreeNode* root, vector<int>& to_delete) {
        queue<TreeNode*> nodes;
        vector<TreeNode*> ret;
        unordered_set<int> deletes_set;

        nodes.push(root);
        for(auto val : to_delete)
            deletes_set.insert(val);

        while(!nodes.empty()) {
            TreeNode* tmp = nodes.front();
            nodes.pop();

            if(find(deletes_set.begin(), deletes_set.end(), tmp->val) != deletes_set.end()) {
                if(tmp->left)
                    nodes.push(tmp->left);
                if(tmp->right)
                    nodes.push(tmp->right);
                delete(tmp);
            } else {
                traverse(tmp, &nodes, deletes_set);
                ret.push_back(tmp);
            }
        }

        return ret;   
    }
};
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