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https://github.com/krahets/hello-algo.git
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7cdfa03e68
* feat(kotlin):new kotlin support files
* fix(kotlin):
reviewed the formatting, comments and so on.
* fix(kotlin): fix the indentation and format
* feat(kotlin): Add kotlin code for the backtraking chapter.
* fix(kotlin): fix incorrect output of preorder_traversal_iii_template.kt file
* fix(kotlin): simplify kotlin codes
* fix(kotlin): modify n_queens.kt for consistency.
* feat(kotlin): add kotlin code for computational complexity.
* fix(kotlin): remove iteration folder.
* fix(kotlin): remove n_queens.kt file out of folder.
* fix(kotlin): remove some folders.
* style(kotlin): modified two chapters.
* feat(kotlin): add kotlin code for divide and conquer.
* Update build_tree.kt
* Update hanota.kt
* Delete codes/kotlin/chapter_backtracking directory
* Delete codes/kotlin/chapter_computational_complexity directory
* Delete codes/kotlin/chapter_divide_and_conquer directory
* feat(kotlin): add kotlin code for divide and conquer.
* Update hanota.kt
49 lines
No EOL
1.4 KiB
Kotlin
49 lines
No EOL
1.4 KiB
Kotlin
/**
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* File: build_tree.kt
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* Created Time: 2024-01-25
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* Author: curtishd (1023632660@qq.com)
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*/
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package chapter_divide_and_conquer.build_tree
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import utils.TreeNode
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import utils.printTree
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/* 构建二叉树：分治 */
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fun dfs(preorder: IntArray, inorderMap: Map<Int?, Int?>, i: Int, l: Int, r: Int): TreeNode? {
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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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val root = TreeNode(preorder[i])
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// 查询 m ，从而划分左右子树
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val m = inorderMap[preorder[i]]!!
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// 子问题：构建左子树
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root.left = dfs(preorder, inorderMap, 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, inorderMap, 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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fun buildTree(preorder: IntArray, inorder: IntArray): 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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val inorderMap: MutableMap<Int?, Int?> = HashMap()
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for (i in inorder.indices) {
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inorderMap[inorder[i]] = i
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}
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val root = dfs(preorder, inorderMap, 0, 0, inorder.size - 1)
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return root
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}
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/* Driver Code */
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fun main() {
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val preorder = intArrayOf(3, 9, 2, 1, 7)
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val inorder = intArrayOf(9, 3, 1, 2, 7)
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println("前序遍历 = " + preorder.contentToString())
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println("中序遍历 = " + inorder.contentToString())
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val root = buildTree(preorder, inorder)
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println("构建的二叉树为：")
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printTree(root)
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} |