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# @Title: 根据描述创建二叉树 (Create Binary Tree From Descriptions)
# @Author: 15816537946@163.com
# @Date: 2022-03-06 14:13:11
# @Runtime: 616 ms
# @Memory: 22.6 MB
class Solution:
    def createBinaryTree(self, descriptions: List[List[int]]) -> Optional[TreeNode]:
        v = dict()
        deg = collections.Counter()
        for p, c, left in descriptions:
            if p not in v:
                v[p] = TreeNode(p)
            if c not in v:
                v[c] = TreeNode(c)
            if left == 1:
                v[p].left = v[c]
            else:
                v[p].right = v[c]
            deg[c] += 1
        for i in v:
            if deg[i] == 0:
                return v[i]
        
        return None