<p>You are given a 2D integer array <code>descriptions</code> where <code>descriptions[i] = [parent<sub>i</sub>, child<sub>i</sub>, isLeft<sub>i</sub>]</code> indicates that <code>parent<sub>i</sub></code> is the <strong>parent</strong> of <code>child<sub>i</sub></code> in a <strong>binary</strong> tree of <strong>unique</strong> values. Furthermore,</p>

<ul>
	<li>If <code>isLeft<sub>i</sub> == 1</code>, then <code>child<sub>i</sub></code> is the left child of <code>parent<sub>i</sub></code>.</li>
	<li>If <code>isLeft<sub>i</sub> == 0</code>, then <code>child<sub>i</sub></code> is the right child of <code>parent<sub>i</sub></code>.</li>
</ul>

<p>Construct the binary tree described by <code>descriptions</code> and return <em>its <strong>root</strong></em>.</p>

<p>The test cases will be generated such that the binary tree is <strong>valid</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2022/02/09/example1drawio.png" style="width: 300px; height: 236px;" />
<pre>
<strong>Input:</strong> descriptions = [[20,15,1],[20,17,0],[50,20,1],[50,80,0],[80,19,1]]
<strong>Output:</strong> [50,20,80,15,17,19]
<strong>Explanation:</strong> The root node is the node with value 50 since it has no parent.
The resulting binary tree is shown in the diagram.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2022/02/09/example2drawio.png" style="width: 131px; height: 300px;" />
<pre>
<strong>Input:</strong> descriptions = [[1,2,1],[2,3,0],[3,4,1]]
<strong>Output:</strong> [1,2,null,null,3,4]
<strong>Explanation:</strong> The root node is the node with value 1 since it has no parent.
The resulting binary tree is shown in the diagram.
</pre>

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

<ul>
	<li><code>1 &lt;= descriptions.length &lt;= 10<sup>4</sup></code></li>
	<li><code>descriptions[i].length == 3</code></li>
	<li><code>1 &lt;= parent<sub>i</sub>, child<sub>i</sub> &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= isLeft<sub>i</sub> &lt;= 1</code></li>
	<li>The binary tree described by <code>descriptions</code> is valid.</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 {
private:
int findRootNode(vector<vector<int>>& descriptions) {
    unordered_set<int> childNodes;
    unordered_set<int> allNodes;
    
    //Store child nodes and all nodes in separate sets
    for(int i=0;i<descriptions.size();i++) 
    {
        allNodes.insert(descriptions[i][0]);  
        childNodes.insert(descriptions[i][1]); 
    }
    
    //The root node will be present in allNodes but not in childNodes
    for (int node : allNodes) 
    {
        if (childNodes.find(node) == childNodes.end()) 
        {
            return node;
        }
    }
    
    return -1;  //no valid root node found
}
    // TreeNode* solve(vector<vector<int>>& descriptions,TreeNode* root)
    // {
    //     for(int i=0;i<descriptions.size();i++)
    //     {
    //         if(root->val==descriptions[i][0])
    //         {
    //             if(descriptions[i][2])
    //             {
    //                 TreeNode* left=new TreeNode(descriptions[i][1]);
    //                 root->left=left;
    //                 solve(descriptions,left);
    //             }
    //             else
    //             {
    //                 TreeNode* right=new TreeNode(descriptions[i][1]);
    //                 root->right=right;  
    //                 solve(descriptions,right);                 
    //             }
    //         }
    //     }
    //     return root;
    // }
public:
    TreeNode* createBinaryTree(vector<vector<int>>& descriptions) {

        // int rootVal=findRootNode(descriptions);
        // TreeNode* root=new TreeNode(rootVal);

        // return solve(descriptions,root);

        
        unordered_map<int, TreeNode*> nodeMap;
        
        // Create all nodes and establish parent-child relationships
        for (int i=0;i<descriptions.size();i++) 
        {
            int parentVal = descriptions[i][0];
            int childVal = descriptions[i][1];
            bool isLeft = descriptions[i][2];

            // Create parent node if it doesn't exist
            if (nodeMap.find(parentVal) == nodeMap.end()) {
                nodeMap[parentVal] = new TreeNode(parentVal);
            }

            // Create child node if it doesn't exist
            if (nodeMap.find(childVal) == nodeMap.end()) {
                nodeMap[childVal] = new TreeNode(childVal);
            }

            // Link parent to child
            if (isLeft) 
            {
                nodeMap[parentVal]->left = nodeMap[childVal];
            } 
            else 
            {
                nodeMap[parentVal]->right = nodeMap[childVal];
            }
        }
        
        // Find the root node
        int rootVal = findRootNode(descriptions);
        return nodeMap[rootVal];
    }
};
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