1#include <unordered_map>
2#include <unordered_set>
3#include <vector>
4using namespace std;
5
6class TreeNode {
7public:
8    int val;
9    TreeNode* left;
10    TreeNode* right;
11    TreeNode(int value) : val(value), left(nullptr), right(nullptr) {}
12};
13
14class Solution {
15public:
16    TreeNode* createBinaryTree(vector<vector<int>>& descriptions) {
17        unordered_map<int, TreeNode*> nodes;
18        unordered_set<int> children;
19
20        for (const auto& desc : descriptions) {
21            int parent = desc[0], child = desc[1], isLeft = desc[2];
22            if (nodes.find(parent) == nodes.end())
23                nodes[parent] = new TreeNode(parent);
24            if (nodes.find(child) == nodes.end())
25                nodes[child] = new TreeNode(child);
26
27            if (isLeft) {
28                nodes[parent]->left = nodes[child];
29            } else {
30                nodes[parent]->right = nodes[child];
31            }
32
33            children.insert(child);
34        }
35
36        for (const auto& [key, node] : nodes) {
37            if (children.find(key) == children.end()) {
38                return node;
39            }
40        }
41
42        return nullptr;
43    }
44};
45

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;
    }
}