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45 lines
1.4 KiB
45 lines
1.4 KiB
8 months ago
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/**
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* File: build_tree.js
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* Created Time: 2023-07-30
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* Author: yuan0221 (yl1452491917@gmail.com)
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*/
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const { printTree } = require('../modules/PrintUtil');
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const { TreeNode } = require('../modules/TreeNode');
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/* 構建二元樹：分治 */
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function dfs(preorder, inorderMap, i, l, r) {
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// 子樹區間為空時終止
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if (r - l < 0) return null;
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// 初始化根節點
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const root = new TreeNode(preorder[i]);
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// 查詢 m ，從而劃分左右子樹
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const m = inorderMap.get(preorder[i]);
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// 子問題：構建左子樹
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root.left = dfs(preorder, inorderMap, i + 1, l, m - 1);
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// 子問題：構建右子樹
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root.right = dfs(preorder, inorderMap, i + 1 + m - l, m + 1, r);
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// 返回根節點
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return root;
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}
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/* 構建二元樹 */
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function buildTree(preorder, inorder) {
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// 初始化雜湊表，儲存 inorder 元素到索引的對映
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let inorderMap = new Map();
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for (let i = 0; i < inorder.length; i++) {
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inorderMap.set(inorder[i], i);
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}
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const root = dfs(preorder, inorderMap, 0, 0, inorder.length - 1);
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return root;
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}
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/* Driver Code */
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const preorder = [3, 9, 2, 1, 7];
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const inorder = [9, 3, 1, 2, 7];
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console.log('前序走訪 = ' + JSON.stringify(preorder));
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console.log('中序走訪 = ' + JSON.stringify(inorder));
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const root = buildTree(preorder, inorder);
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console.log('構建的二元樹為：');
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printTree(root);
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