1#include <stdio.h>
2#include <stdlib.h>
3#include <stdbool.h>
4
5typedef struct TreeNode {
6    int val;
7    struct TreeNode *left;
8    struct TreeNode *right;
9} TreeNode;
10
11TreeNode* createNode(int val) {
12    TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
13    node->val = val;
14    node->left = NULL;
15    node->right = NULL;
16    return node;
17}
18
19TreeNode* createBinaryTree(int** descriptions, int descriptionsSize, int* descriptionsColSize) {
20    TreeNode* nodes[100000] = { NULL };
21    bool isChild[100000] = { false };
22
23    for (int i = 0; i < descriptionsSize; ++i) {
24        int parentVal = descriptions[i][0], childVal = descriptions[i][1], isLeft = descriptions[i][2];
25
26        if (nodes[parentVal] == NULL) {
27            nodes[parentVal] = createNode(parentVal);
28        }
29
30        if (nodes[childVal] == NULL) {
31            nodes[childVal] = createNode(childVal);
32        }
33
34        if (isLeft) {
35            nodes[parentVal]->left = nodes[childVal];
36        } else {
37            nodes[parentVal]->right = nodes[childVal];
38        }
39
40        isChild[childVal] = true;
41    }
42
43    for (int i = 0; i < 100000; ++i) {
44        if (nodes[i] != NULL && !isChild[i]) {
45            return nodes[i];  // This node is not a child, hence it must be the root
46        }
47    }
48
49    return NULL;
50}
51

1#include <unordered_set>
#include <vector>
using namespace std;

class TreeNode {
public:
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int value) : val(value), left(nullptr), right(nullptr) {}
};

class Solution {
public:
    TreeNode* createBinaryTree(vector<vector<int>>& descriptions) {
        unordered_map<int, TreeNode*> nodes;
        unordered_set<int> children;

        // First pass to create all tree nodes
        for (const auto& desc : descriptions) {
            if (nodes.find(desc[0]) == nodes.end())
                nodes[desc[0]] = new TreeNode(desc[0]);
            if (nodes.find(desc[1]) == nodes.end())
                nodes[desc[1]] = new TreeNode(desc[1]);

            children.insert(desc[1]);
        }

        // Second pass to link tree nodes
        for (const auto& desc : descriptions) {
            int parent = desc[0], child = desc[1], isLeft = desc[2];

            if (isLeft) {
                nodes[parent]->left = nodes[child];
            } else {
                nodes[parent]->right = nodes[child];
            }
        }

        for (const auto& [key, node] : nodes) {
            if (children.find(key) == children.end()) {
                return node;
            }
        }

        return nullptr;
    }
};