1class TreeNode:
2    def __init__(self, val=0, left=None, right=None):
3        self.val = val
4        self.left = left
5        self.right = right
6
7class Solution:
8    def createBinaryTree(self, descriptions):
9        nodeMap = {}
10        children = set()
11
12        for parent, child, isLeft in descriptions:
13            if parent not in nodeMap:
14                nodeMap[parent] = TreeNode(parent)
15            if child not in nodeMap:
16                nodeMap[child] = TreeNode(child)
17            
18            if isLeft:
19                nodeMap[parent].left = nodeMap[child]
20            else:
21                nodeMap[parent].right = nodeMap[child]
22
23            children.add(child)
24
25        # Find the root
26        for key in nodeMap:
27            if key not in children:
28                return nodeMap[key]
29
30        return None
31

1using 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;
    }
}