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38 lines
1.0 KiB
38 lines
1.0 KiB
// File: build_tree.go
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// Created Time: 2023-07-20
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// Author: hongyun-robot (1836017030@qq.com)
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package chapter_divide_and_conquer
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import . "github.com/krahets/hello-algo/pkg"
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/* 构建二叉树：分治 */
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func dfsBuildTree(preorder, inorder []int, hmap map[int]int, i, l, r int) *TreeNode {
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// 子树区间为空时终止
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if r-l < 0 {
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return nil
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}
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// 初始化根节点
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root := NewTreeNode(preorder[i])
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// 查询 m ，从而划分左右子树
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m := hmap[preorder[i]]
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// 子问题：构建左子树
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root.Left = dfsBuildTree(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 = dfsBuildTree(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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func buildTree(preorder, inorder []int) *TreeNode {
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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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hmap := make(map[int]int, len(inorder))
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for i := 0; i < len(inorder); i++ {
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hmap[inorder[i]] = i
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}
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root := dfsBuildTree(preorder, inorder, hmap, 0, 0, len(inorder)-1)
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return root
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}
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