![\"\"](\"https://assets.leetcode.com/uploads/2022/02/09/example1drawio.png\")
You are given a 2D integer array descriptions where descriptions[i] = [parenti, childi, isLefti] indicates that parenti is the parent of childi in a binary tree of unique values. Furthermore,
isLefti == 1, then childi is the left child of parenti.isLefti == 0, then childi is the right child of parenti.Construct the binary tree described by descriptions and return its root.
The test cases will be generated such that the binary tree is valid.
\n\n\n
Example 1:
\n\n\nInput: descriptions = [[20,15,1],[20,17,0],[50,20,1],[50,80,0],[80,19,1]]\nOutput: [50,20,80,15,17,19]\nExplanation: The root node is the node with value 50 since it has no parent.\nThe resulting binary tree is shown in the diagram.\n\n\n
Example 2:
\n![\"\"](\"https://assets.leetcode.com/uploads/2022/02/09/example2drawio.png\")
\n\nInput: descriptions = [[1,2,1],[2,3,0],[3,4,1]]\nOutput: [1,2,null,null,3,4]\nExplanation: The root node is the node with value 1 since it has no parent.\nThe resulting binary tree is shown in the diagram.\n\n\n
\n
Constraints:
\n\n1 <= descriptions.length <= 104descriptions[i].length == 31 <= parenti, childi <= 1050 <= isLefti <= 1descriptions is valid.给你一个二维整数数组 descriptions ，其中 descriptions[i] = [parenti, childi, isLefti] 表示 parenti 是 childi 在 二叉树 中的 父节点，二叉树中各节点的值 互不相同 。此外：
isLefti == 1 ，那么 childi 就是 parenti 的左子节点。isLefti == 0 ，那么 childi 就是 parenti 的右子节点。请你根据 descriptions 的描述来构造二叉树并返回其 根节点 。
测试用例会保证可以构造出 有效 的二叉树。
\n\n\n\n
示例 1：
\n\n
\n输入：descriptions = [[20,15,1],[20,17,0],[50,20,1],[50,80,0],[80,19,1]]\n输出：[50,20,80,15,17,19]\n解释：根节点是值为 50 的节点，因为它没有父节点。\n结果二叉树如上图所示。\n\n\n
示例 2：
\n\n
\n输入：descriptions = [[1,2,1],[2,3,0],[3,4,1]]\n输出：[1,2,null,null,3,4]\n解释：根节点是值为 1 的节点，因为它没有父节点。 \n结果二叉树如上图所示。\n\n
\n\n
提示：
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"style": "LEETCODE",
"exampleTestcases": "[[20,15,1],[20,17,0],[50,20,1],[50,80,0],[80,19,1]]\n[[1,2,1],[2,3,0],[3,4,1]]",
"__typename": "QuestionNode"
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