1using System;
2using System.Collections.Generic;
3
4public class TreeNode {
5    public int val;
6    public TreeNode left;
7    public TreeNode right;
8    public TreeNode(int val = 0, TreeNode left = null, TreeNode right = null) {
9        this.val = val;
10        this.left = left;
11        this.right = right;
12    }
13}
14
15public class Solution {
16    public TreeNode CreateBinaryTree(int[][] descriptions) {
17        Dictionary<int, TreeNode> nodeMap = new Dictionary<int, TreeNode>();
18        HashSet<int> children = new HashSet<int>();
19
20        foreach (var desc in descriptions) {
21            int parent = desc[0], child = desc[1], isLeft = desc[2];
22            if (!nodeMap.ContainsKey(parent)) {
23                nodeMap[parent] = new TreeNode(parent);
24            }
25            if (!nodeMap.ContainsKey(child)) {
26                nodeMap[child] = new TreeNode(child);
27            }
28
29            if (isLeft == 1) {
30                nodeMap[parent].left = nodeMap[child];
31            } else {
32                nodeMap[parent].right = nodeMap[child];
33            }
34            
35            children.Add(child);
36        }
37
38        foreach (var key in nodeMap.Keys) {
39            if (!children.Contains(key)) {
40                return nodeMap[key];
41            }
42        }
43
44        return null;
45    }
46}
47

1