mirror of
https://github.com/krahets/hello-algo.git
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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
"""
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File: build_tree.py
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Created Time: 2023-07-15
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Author: krahets (krahets@163.com)
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"""
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import sys
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from pathlib import Path
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sys.path.append(str(Path(__file__).parent.parent))
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from modules import TreeNode, print_tree
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def dfs(
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preorder: list[int],
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inorder_map: dict[int, int],
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i: int,
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l: int,
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r: int,
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) -> TreeNode | None:
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"""二分木の構築：分割統治"""
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# 部分木の区間が空のとき終了
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if r - l < 0:
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return None
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# ルートノードを初期化
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root = TreeNode(preorder[i])
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# m をクエリして左部分木と右部分木を分割
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m = inorder_map[preorder[i]]
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# 部分問題：左部分木を構築
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root.left = dfs(preorder, inorder_map, i + 1, l, m - 1)
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# 部分問題：右部分木を構築
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root.right = dfs(preorder, inorder_map, i + 1 + m - l, m + 1, r)
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# ルートノードを返す
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return root
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def build_tree(preorder: list[int], inorder: list[int]) -> TreeNode | None:
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"""二分木を構築"""
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# 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
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inorder_map = {val: i for i, val in enumerate(inorder)}
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root = dfs(preorder, inorder_map, 0, 0, len(inorder) - 1)
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return root
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"""ドライバーコード"""
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if __name__ == "__main__":
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preorder = [3, 9, 2, 1, 7]
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inorder = [9, 3, 1, 2, 7]
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print(f"前順走査 = {preorder}")
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print(f"中順走査 = {inorder}")
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root = build_tree(preorder, inorder)
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print("構築された二分木は：")
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print_tree(root) |