38 lines
1.1 KiB
Go
38 lines
1.1 KiB
Go
// 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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/* Build binary tree: Divide and conquer */
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func dfsBuildTree(preorder []int, inorderMap map[int]int, i, l, r int) *TreeNode {
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// Terminate when subtree interval is empty
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if r-l < 0 {
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return nil
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}
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// Initialize root node
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root := NewTreeNode(preorder[i])
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// Query m to divide left and right subtrees
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m := inorderMap[preorder[i]]
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// Subproblem: build left subtree
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root.Left = dfsBuildTree(preorder, inorderMap, i+1, l, m-1)
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// Subproblem: build right subtree
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root.Right = dfsBuildTree(preorder, inorderMap, i+1+m-l, m+1, r)
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// Return root node
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return root
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}
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/* Build binary tree */
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func buildTree(preorder, inorder []int) *TreeNode {
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// Initialize hash table, storing in-order elements to indices mapping
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inorderMap := make(map[int]int, len(inorder))
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for i := 0; i < len(inorder); i++ {
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inorderMap[inorder[i]] = i
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}
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root := dfsBuildTree(preorder, inorderMap, 0, 0, len(inorder)-1)
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return root
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}
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