1class TreeNode {
2    constructor(val, left = null, right = null) {
3        this.val = val;
4        this.left = left;
5        this.right = right;
6    }
7}
8
9function createBinaryTree(descriptions) {
10    const nodeMap = new Map();
11    const children = new Set();
12
13    for (const [parent, child, isLeft] of descriptions) {
14        if (!nodeMap.has(parent)) {
15            nodeMap.set(parent, new TreeNode(parent));
16        }
17        if (!nodeMap.has(child)) {
18            nodeMap.set(child, new TreeNode(child));
19        }
20
21        if (isLeft === 1) {
22            nodeMap.get(parent).left = nodeMap.get(child);
23        } else {
24            nodeMap.get(parent).right = nodeMap.get(child);
25        }
26        children.add(child);
27    }
28
29    for (const [key, node] of nodeMap) {
30        if (!children.has(key)) {
31            return node;
32        }
33    }
34    return null;
35}
36

using System.Collections.Generic;

public class TreeNode {
    public int val;
    public TreeNode left;
    public TreeNode right;
    public TreeNode(int val = 0, TreeNode left = null, TreeNode right = null) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

public class Solution {
    public TreeNode CreateBinaryTree(int[][] descriptions) {
        Dictionary<int, TreeNode> nodeMap = new Dictionary<int, TreeNode>();
        HashSet<int> children = new HashSet<int>();

        // First pass: Create all nodes
        foreach (var desc in descriptions) {
            int parent = desc[0], child = desc[1];
            if (!nodeMap.ContainsKey(parent))
                nodeMap[parent] = new TreeNode(parent);
            if (!nodeMap.ContainsKey(child))
                nodeMap[child] = new TreeNode(child);
            children.Add(child);
        }

        // Second pass: Link nodes
        foreach (var desc in descriptions) {
            int parent = desc[0], child = desc[1], isLeft = desc[2];

            if (isLeft == 1) {
                nodeMap[parent].left = nodeMap[child];
            } else {
                nodeMap[parent].right = nodeMap[child];
            }
        }

        foreach (var key in nodeMap.Keys) {
            if (!children.Contains(key)) {
                return nodeMap[key];
            }
        }

        return null;
    }
}