<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 {
public:
    int findMainRoot( vector<int>& parent, vector<int>& children ){
        for( int i=0; i<parent.size(); i++){
            if( (find(children.begin(), children.end(), parent[i])-children.begin())==children.size() ){
                return parent[i];
            }
        }
        return 0;
    }
    

    TreeNode* createBinaryTree(vector<vector<int>>& descriptions) {
        map<int,int> leftChild;
        map<int,int> rightChild;
        vector<int> children;
        vector<int> parent;

        //Take out the parent - left and right child relationships from descriptions

        for ( int i=0; i<descriptions.size(); i++ ){
            if( descriptions[i][2]==1 ){
                leftChild[descriptions[i][0]]=descriptions[i][1];
            }
            else{
                rightChild[descriptions[i][0]]=descriptions[i][1];
            }
            children.push_back(descriptions[i][1]);
            parent.push_back(descriptions[i][0]);
        }

        int root = findMainRoot(parent, children);
        cout<<root<<endl;

        //Build the tree using the concept of level order traversal and building

        queue<TreeNode*> input;
        TreeNode* mainRoot = new TreeNode(root);
        input.push(mainRoot);
        while(!input.empty()){
            TreeNode* temp = input.front();
            input.pop();

            if( leftChild[temp->val]!=0 ){
                temp->left = new TreeNode(leftChild[temp->val]);
                input.push(temp->left);
            }
            if( rightChild[temp->val]!=0 ){
                temp->right = new TreeNode(rightChild[temp->val]);
                input.push(temp->right);
            }

        }
        return mainRoot;
    }
};
290525