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Update bt_construct_inorder_preorder.py

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bt3gl 2023-08-08 14:43:04 -07:00 committed by GitHub
parent 83fc152596
commit e5efd5424a
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1 changed files with 8 additions and 8 deletions
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trees/bt_construct_inorder_preorder.py
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@ -2,24 +2,24 @@
# -*- coding: utf-8 -*- # -*- coding: utf-8 -*-
# author: bt3gl # author: bt3gl
def build_tree(preorder: list[int], inorder: list[int]) -> Optional[Node]:
def helper(i_left, i_right, index_map): def build_tree(preorder, inorder) -> Optional[Node]:
if i_left > i_right: def helper(left, right, index_map):
if left > right:
return None return None
root = TreeNode(preorder.pop(0)) root = Node(preorder.pop(0))
index_here = index_map[root.val] index_here = index_map[root.val]
# this order change from postorder # this order change from postorder
root.left = helper(i_left, index_here - 1, index_map) root.left = helper(left, index_here - 1, index_map)
root.right = helper(index_here + 1, i_right, index_map) root.right = helper(index_here + 1, right, index_map)
return root return root
index_map = {value: i for i, value in enumerate(inorder)}
index_map = {value: index for index, value in enumerate(inorder)}
return helper(0, len(inorder) - 1, index_map) return helper(0, len(inorder) - 1, index_map)