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Update construct_tree_inorder_postorder.py

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bt3gl 2023-07-30 15:51:43 -07:00 committed by GitHub
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commit 38cbe1c55b
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1 changed files with 15 additions and 11 deletions
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trees_and_graphs/construct_tree_inorder_postorder.py
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# author: bt3gl
# Given two integer arrays inorder and postorder where inorder is the inorder # Given two integer arrays inorder and postorder where inorder is the inorder
# traversal of a binary tree and postorder is the postorder traversal of the # traversal of a binary tree and postorder is the postorder traversal of the
# same tree, construct and return the binary tree. # same tree, construct and return the binary tree.
def build_tree(inorder: list[int], postorder: list[int]) -> Optional[TreeNode]:
def fill_tree(i_left, i_right, inorder_map): def fill_tree(i_left, i_right, inorder_map):
if i_left > i_right: if i_left > i_right:
return None return None
val = postorder.pop() val = postorder.pop()
root = TreeNode(val) root = TreeNode(val)
index_here = inorder_map[val] index_here = inorder_map[val]
root.right = fill_tree(index_here + 1, i_right, inorder_map) root.right = fill_tree(index_here + 1, i_right, inorder_map)
root.left = fill_tree(i_left, index_here - 1, inorder_map) root.left = fill_tree(i_left, index_here - 1, inorder_map)
return root return root
def build_tree(inorder: list[int], postorder: list[int]) -> Optional[TreeNode]:
inorder_map = {val: index for index, val in enumerate(inorder)} inorder_map = {val: index for index, val in enumerate(inorder)}
return fill_tree(0, len(inorder) - 1, inorder_map) return fill_tree(0, len(inorder) - 1, inorder_map)