<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>

/**
 * 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) 
    {
        unordered_set<int> dels (to_delete.begin(), to_delete.end());
        vector<TreeNode*> result;
        if (dels.count(root->val) == 0)
        {
            result.push_back(root);
        }
        delNodeHelper(root, dels, result);

        return result;
    }

private:
    void delNodeHelper(TreeNode* node, unordered_set<int> dels, vector<TreeNode*>& result)
    {
        if (!node)
        {
            return;
        }

        if (!node->left && !node->right)
        {
            return;
        }

        delNodeHelper(node->left, dels, result);
        delNodeHelper(node->right, dels, result);

        if (node->left)
        {
            int leftVal = node->left->val;
            auto leftCapture = node->left;
            if (dels.count(leftVal) != 0)
            {
                node->left = NULL;
            }
        }

        if (node->right)
        {
            int rightVal = node->right->val;
            auto rightCapture = node->right;
            if (dels.count(rightVal) != 0)
            {
                node->right = NULL;
            }
        }
        
        if (dels.count(node->val) != 0)
        {
            if (node->left)
            {
                result.push_back(node->left);
            }
            if (node->right)
            {
                result.push_back(node->right);
            }
        }
    }
};
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