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25 lines
727 B
Python
25 lines
727 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, inorder) -> Optional[Node]:
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def helper(left, right, index_map):
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if left > right:
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return None
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root = Node(preorder.pop(0)) # # this order change from postorder
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index_here = index_map[root.val]
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root.left = helper(left, index_here - 1, index_map) # this order change from postorder
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root.right = helper(index_here + 1, right, index_map)
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return root
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index_map = {value: i for i, value in enumerate(inorder)}
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return helper(0, len(inorder) - 1, index_map)
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