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45 lines
1.4 KiB
45 lines
1.4 KiB
1 year 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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/* 构建二叉树：分治 */
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function dfs(preorder, inorder, hmap, i, l, r) {
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// 子树区间为空时终止
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if (r - l < 0) return null;
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// 初始化根节点
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const root = new TreeNode(preorder[i]);
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// 查询 m ，从而划分左右子树
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const m = hmap.get(preorder[i]);
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// 子问题：构建左子树
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root.left = dfs(preorder, inorder, hmap, i + 1, l, m - 1);
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// 子问题：构建右子树
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root.right = dfs(preorder, inorder, hmap, i + 1 + m - l, m + 1, r);
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// 返回根节点
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return root;
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}
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/* 构建二叉树 */
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function buildTree(preorder, inorder) {
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// 初始化哈希表，存储 inorder 元素到索引的映射
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let hmap = new Map();
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for (let i = 0; i < inorder.length; i++) {
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hmap.set(inorder[i], i);
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}
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const root = dfs(preorder, inorder, hmap, 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('前序遍历 = ' + JSON.stringify(preorder));
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console.log('中序遍历 = ' + JSON.stringify(inorder));
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const root = buildTree(preorder, inorder);
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console.log('构建的二叉树为：');
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printTree(root);
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