# https://leetcode.com/problems/create-binary-tree-from-descriptions
from typing import Dict, List, Optional

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right
class Solution:
    def createBinaryTree(self, descriptions: List[List[int]]) -> Optional[TreeNode]:
        nodes: Dict[int, TreeNode] = {}
        s = set()
        for head, next, left in descriptions:
            if nodes.get(head) is None:
                nodes[head] = TreeNode(head)
            if nodes.get(next) is None:
                nodes[next] = TreeNode(next)
            if left:
                nodes[head].left = nodes[next]
            else:
                nodes[head].right = nodes[next]
            s.add(next)
        for node in nodes:
            if node not in s:
                return nodes[node]