{ "data": { "question": { "questionId": "775", "questionFrontendId": "589", "boundTopicId": null, "title": "N-ary Tree Preorder Traversal", "titleSlug": "n-ary-tree-preorder-traversal", "content": "

Given the root of an n-ary tree, return the preorder traversal of its nodes' values.

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Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)

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Example 1:

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\nInput: root = [1,null,3,2,4,null,5,6]\nOutput: [1,3,5,6,2,4]\n
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Example 2:

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\"\"

\n\n
\nInput: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]\nOutput: [1,2,3,6,7,11,14,4,8,12,5,9,13,10]\n
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Constraints:

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Follow up: Recursive solution is trivial, could you do it iteratively?

\n", "translatedTitle": null, "translatedContent": null, "isPaidOnly": false, "difficulty": "Easy", "likes": 3063, "dislikes": 199, "isLiked": null, "similarQuestions": "[{\"title\": \"Binary Tree Preorder Traversal\", \"titleSlug\": \"binary-tree-preorder-traversal\", \"difficulty\": \"Easy\", \"translatedTitle\": null}, {\"title\": \"N-ary Tree Level Order Traversal\", \"titleSlug\": \"n-ary-tree-level-order-traversal\", \"difficulty\": \"Medium\", \"translatedTitle\": null}, {\"title\": \"N-ary Tree Postorder Traversal\", \"titleSlug\": \"n-ary-tree-postorder-traversal\", \"difficulty\": \"Easy\", \"translatedTitle\": null}]", "exampleTestcases": "[1,null,3,2,4,null,5,6]\n[1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]", "categoryTitle": "Algorithms", "contributors": [], "topicTags": [ { "name": "Stack", "slug": "stack", "translatedName": null, "__typename": "TopicTagNode" }, { "name": "Tree", "slug": "tree", "translatedName": null, "__typename": "TopicTagNode" }, { "name": "Depth-First Search", "slug": "depth-first-search", "translatedName": null, "__typename": "TopicTagNode" } ], "companyTagStats": null, "codeSnippets": [ { "lang": "C++", "langSlug": "cpp", "code": "/*\n// Definition for a Node.\nclass Node {\npublic:\n int val;\n vector children;\n\n Node() {}\n\n Node(int _val) {\n val = _val;\n }\n\n Node(int _val, vector _children) {\n val = _val;\n children = _children;\n }\n};\n*/\n\nclass Solution {\npublic:\n vector preorder(Node* root) {\n \n }\n};", "__typename": "CodeSnippetNode" }, { "lang": "Java", "langSlug": "java", "code": "/*\n// Definition for a Node.\nclass Node {\n public int val;\n public List children;\n\n public Node() {}\n\n public Node(int _val) {\n val = _val;\n }\n\n public Node(int _val, List _children) {\n val = _val;\n children = _children;\n }\n};\n*/\n\nclass Solution {\n public List preorder(Node root) {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "lang": "Python", "langSlug": "python", "code": "\"\"\"\n# Definition for a Node.\nclass Node(object):\n def __init__(self, val=None, children=None):\n self.val = val\n self.children = children\n\"\"\"\n\nclass Solution(object):\n def preorder(self, root):\n \"\"\"\n :type root: Node\n :rtype: List[int]\n \"\"\"\n ", "__typename": "CodeSnippetNode" }, { "lang": "Python3", "langSlug": "python3", "code": "\"\"\"\n# Definition for a Node.\nclass Node:\n def __init__(self, val=None, children=None):\n self.val = val\n self.children = children\n\"\"\"\n\nclass Solution:\n def preorder(self, root: 'Node') -> List[int]:\n ", "__typename": "CodeSnippetNode" }, { "lang": "C", "langSlug": "c", "code": "/**\n * Definition for a Node.\n * struct Node {\n * int val;\n * int numChildren;\n * struct Node** children;\n * };\n */\n\n/**\n * Note: The returned array must be malloced, assume caller calls free().\n */\nint* preorder(struct Node* root, int* returnSize) {\n \n}", "__typename": "CodeSnippetNode" }, { "lang": "C#", "langSlug": "csharp", "code": "/*\n// Definition for a Node.\npublic class Node {\n public int val;\n public IList children;\n\n public Node() {}\n\n public Node(int _val) {\n val = _val;\n }\n\n public Node(int _val,IList _children) {\n val = _val;\n children = _children;\n }\n}\n*/\n\npublic class Solution {\n public IList Preorder(Node root) {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "lang": "JavaScript", "langSlug": "javascript", "code": "/**\n * // Definition for a Node.\n * function Node(val, children) {\n * this.val = val;\n * this.children = children;\n * };\n */\n\n/**\n * @param {Node|null} root\n * @return {number[]}\n */\nvar preorder = function(root) {\n \n};", "__typename": "CodeSnippetNode" }, { "lang": "TypeScript", "langSlug": "typescript", "code": "/**\n * Definition for node.\n * class Node {\n * val: number\n * children: Node[]\n * constructor(val?: number) {\n * this.val = (val===undefined ? 0 : val)\n * this.children = []\n * }\n * }\n */\n\nfunction preorder(root: Node | null): number[] {\n\n};", "__typename": "CodeSnippetNode" }, { "lang": "PHP", "langSlug": "php", "code": "/**\n * Definition for a Node.\n * class Node {\n * public $val = null;\n * public $children = null;\n * function __construct($val = 0) {\n * $this->val = $val;\n * $this->children = array();\n * }\n * }\n */\n\nclass Solution {\n /**\n * @param Node $root\n * @return integer[]\n */\n function preorder($root) {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "lang": "Swift", "langSlug": "swift", "code": "/**\n * Definition for a Node.\n * public class Node {\n * public var val: Int\n * public var children: [Node]\n * public init(_ val: Int) {\n * self.val = val\n * self.children = []\n * }\n * }\n */\n\nclass Solution {\n func preorder(_ root: Node?) -> [Int] {\n \t\n }\n}", "__typename": "CodeSnippetNode" }, { "lang": "Kotlin", "langSlug": "kotlin", "code": "/**\n * Definition for a Node.\n * class Node(var `val`: Int) {\n * var children: List = listOf()\n * }\n */\n\nclass Solution {\n fun preorder(root: Node?): List {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "lang": "Go", "langSlug": "golang", "code": "/**\n * Definition for a Node.\n * type Node struct {\n * Val int\n * Children []*Node\n * }\n */\n\nfunc preorder(root *Node) []int {\n \n}", "__typename": "CodeSnippetNode" }, { "lang": "Ruby", "langSlug": "ruby", "code": "# Definition for a Node.\n# class Node\n# attr_accessor :val, :children\n# def initialize(val)\n# @val = val\n# @children = []\n# end\n# end\n\n# @param {Node} root\n# @return {List[int]}\ndef preorder(root)\n \nend", "__typename": "CodeSnippetNode" }, { "lang": "Scala", "langSlug": "scala", "code": "/**\n * Definition for a Node.\n * class Node(var _value: Int) {\n * var value: Int = _value\n * var children: List[Node] = List()\n * }\n */\n\nobject Solution {\n def preorder(root: Node): List[Int] = {\n \n }\n}", "__typename": "CodeSnippetNode" } ], "stats": "{\"totalAccepted\": \"412.2K\", \"totalSubmission\": \"547.6K\", \"totalAcceptedRaw\": 412203, \"totalSubmissionRaw\": 547625, \"acRate\": \"75.3%\"}", "hints": [], "solution": { "id": "603", "canSeeDetail": false, "paidOnly": true, "hasVideoSolution": false, "paidOnlyVideo": true, "__typename": "ArticleNode" }, "status": null, "sampleTestCase": "[1,null,3,2,4,null,5,6]", "metaData": "{\n \"name\": \"preorder\",\n \"params\": [\n {\n \"name\": \"root\",\n \"type\": \"integer\"\n }\n ],\n \"return\": {\n \"type\": \"list\"\n },\n \"languages\": [\n \"cpp\",\n \"java\",\n \"python\",\n \"csharp\",\n \"javascript\",\n \"python3\",\n \"golang\",\n \"ruby\",\n \"c\",\n \"kotlin\",\n \"scala\",\n \"php\",\n \"swift\",\n \"typescript\"\n ],\n \"manual\": true\n}", "judgerAvailable": true, "judgeType": "large", "mysqlSchemas": [], "enableRunCode": true, "enableTestMode": false, "enableDebugger": true, "envInfo": "{\"cpp\": [\"C++\", \"

Compiled with clang 11 using the latest C++ 20 standard.

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Your code is compiled with level two optimization (-O2). AddressSanitizer is also enabled to help detect out-of-bounds and use-after-free bugs.

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Most standard library headers are already included automatically for your convenience.

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OpenJDK 17. Java 8 features such as lambda expressions and stream API can be used.

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Most standard library headers are already included automatically for your convenience.

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Includes Pair class from https://docs.oracle.com/javase/8/javafx/api/javafx/util/Pair.html.

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Python 2.7.12.

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Most libraries are already imported automatically for your convenience, such as array, bisect, collections. If you need more libraries, you can import it yourself.

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For Map/TreeMap data structure, you may use sortedcontainers library.

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Note that Python 2.7 will not be maintained past 2020. For the latest Python, please choose Python3 instead.

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Compiled with gcc 8.2 using the gnu11 standard.

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Your code is compiled with level one optimization (-O1). AddressSanitizer is also enabled to help detect out-of-bounds and use-after-free bugs.

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Most standard library headers are already included automatically for your convenience.

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For hash table operations, you may use uthash. \\\"uthash.h\\\" is included by default. Below are some examples:

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1. Adding an item to a hash.\\r\\n

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\\r\\n\\r\\n

3. Deleting an item in a hash:\\r\\n

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C# 10 with .NET 6 runtime

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Node.js 16.13.2.

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Your code is run with --harmony flag, enabling new ES6 features.

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lodash.js library is included by default.

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For Priority Queue / Queue data structures, you may use 5.3.0 version of datastructures-js/priority-queue and 4.2.1 version of datastructures-js/queue.

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Ruby 3.1

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Some common data structure implementations are provided in the Algorithms module: https://www.rubydoc.info/github/kanwei/algorithms/Algorithms

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Swift 5.5.2.

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Go 1.21

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Support https://godoc.org/github.com/emirpasic/gods@v1.18.1 library.

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Python 3.10.

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Scala 2.13.7.

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Kotlin 1.9.0.

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PHP 8.1.

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With bcmath module

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TypeScript 5.1.6, Node.js 16.13.2.

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lodash.js library is included by default.

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