Create Binary Tree From Descriptions LeetCode solution in Python

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class Solution:
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    def createBinaryTree(self, descriptions: List[List[int]]) -> Optional[TreeNode]:
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        hashmap = {}
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        nodes = set()
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        children = set()
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        for parent, child, isLeft in descriptions:
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            nodes.add(parent)
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            nodes.add(child)
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            children.add(child)
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            if parent not in hashmap:
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                hashmap[parent] = TreeNode(parent)
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            if child not in hashmap:
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                hashmap[child] = TreeNode(child)
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            if isLeft:
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                hashmap[parent].left = hashmap[child]
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            if not isLeft:
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                hashmap[parent].right = hashmap[child]
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        for node in nodes:
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            if node not in children:
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                return hashmap[node]