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26 lines
764 B
Python
26 lines
764 B
Python
#!/usr/bin/env python3
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# -*- coding: utf-8 -*-
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# author: bt3gl
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def build_tree(preorder: list[int], inorder: list[int]) -> Optional[TreeNode]:
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def helper(i_left, i_right, index_map):
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if i_left > i_right:
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return None
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root = TreeNode(preorder.pop(0))
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index_here = index_map[root.val]
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# this order change from postorder
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root.left = helper(i_left, index_here - 1, index_map)
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root.right = helper(index_here + 1, i_right, index_map)
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return root
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index_map = {value: index for index, value in enumerate(inorder)}
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return helper(0, len(inorder) - 1, index_map)
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