mirror of
https://github.com/krahets/hello-algo.git
synced 2026-06-28 08:34:28 +00:00
Ikko Eltociear Ashimine
954c45864b
* docs: add Japanese documents (`ja/docs`) * docs: add Japanese documents (`ja/codes`) * docs: add Japanese documents * Remove pythontutor blocks in ja/ * Add an empty at the end of each markdown file. * Add the missing figures (use the English version temporarily). * Add index.md for Japanese version. * Add index.html for Japanese version. * Add missing index.assets * Fix backtracking_algorithm.md for Japanese version. * Add avatar_eltociear.jpg. Fix image links on the Japanese landing page. * Add the Japanese banner. --------- Co-authored-by: krahets <krahets@163.com>
54 lines
1.5 KiB
Python
54 lines
1.5 KiB
Python
"""
|
|
File: build_tree.py
|
|
Created Time: 2023-07-15
|
|
Author: krahets (krahets@163.com)
|
|
"""
|
|
|
|
import sys
|
|
from pathlib import Path
|
|
|
|
sys.path.append(str(Path(__file__).parent.parent))
|
|
from modules import TreeNode, print_tree
|
|
|
|
|
|
def dfs(
|
|
preorder: list[int],
|
|
inorder_map: dict[int, int],
|
|
i: int,
|
|
l: int,
|
|
r: int,
|
|
) -> TreeNode | None:
|
|
"""二分木の構築：分割統治"""
|
|
# 部分木の区間が空のとき終了
|
|
if r - l < 0:
|
|
return None
|
|
# ルートノードを初期化
|
|
root = TreeNode(preorder[i])
|
|
# m をクエリして左部分木と右部分木を分割
|
|
m = inorder_map[preorder[i]]
|
|
# 部分問題：左部分木を構築
|
|
root.left = dfs(preorder, inorder_map, i + 1, l, m - 1)
|
|
# 部分問題：右部分木を構築
|
|
root.right = dfs(preorder, inorder_map, i + 1 + m - l, m + 1, r)
|
|
# ルートノードを返す
|
|
return root
|
|
|
|
|
|
def build_tree(preorder: list[int], inorder: list[int]) -> TreeNode | None:
|
|
"""二分木を構築"""
|
|
# ハッシュテーブルを初期化、中順走査の要素からインデックスへのマッピングを保存
|
|
inorder_map = {val: i for i, val in enumerate(inorder)}
|
|
root = dfs(preorder, inorder_map, 0, 0, len(inorder) - 1)
|
|
return root
|
|
|
|
|
|
"""ドライバーコード"""
|
|
if __name__ == "__main__":
|
|
preorder = [3, 9, 2, 1, 7]
|
|
inorder = [9, 3, 1, 2, 7]
|
|
print(f"前順走査 = {preorder}")
|
|
print(f"中順走査 = {inorder}")
|
|
|
|
root = build_tree(preorder, inorder)
|
|
print("構築された二分木は：")
|
|
print_tree(root) |