{ "data": { "question": { "questionId": "341", "questionFrontendId": "341", "boundTopicId": null, "title": "Flatten Nested List Iterator", "titleSlug": "flatten-nested-list-iterator", "content": "

You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it.

\n\n

Implement the NestedIterator class:

\n\n\n\n

Your code will be tested with the following pseudocode:

\n\n
\ninitialize iterator with nestedList\nres = []\nwhile iterator.hasNext()\n    append iterator.next() to the end of res\nreturn res\n
\n\n

If res matches the expected flattened list, then your code will be judged as correct.

\n\n

 

\n

Example 1:

\n\n
\nInput: nestedList = [[1,1],2,[1,1]]\nOutput: [1,1,2,1,1]\nExplanation: By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].\n
\n\n

Example 2:

\n\n
\nInput: nestedList = [1,[4,[6]]]\nOutput: [1,4,6]\nExplanation: By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].\n
\n\n

 

\n

Constraints:

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list that this NestedInteger holds, if it holds a nested list\n * // The result is undefined if this NestedInteger holds a single integer\n * const vector &getList() const;\n * };\n */\n\nclass NestedIterator {\npublic:\n NestedIterator(vector &nestedList) {\n \n }\n \n int next() {\n \n }\n \n bool hasNext() {\n \n }\n};\n\n/**\n * Your NestedIterator object will be instantiated and called as such:\n * NestedIterator i(nestedList);\n * while (i.hasNext()) cout << i.next();\n */", "__typename": "CodeSnippetNode" }, { "lang": "Java", "langSlug": "java", "code": "/**\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * public interface NestedInteger {\n *\n * // @return true if this NestedInteger holds a single integer, rather than a nested list.\n * public boolean isInteger();\n *\n * // @return the single integer that this NestedInteger holds, if it holds a single integer\n * // Return null if this NestedInteger holds a nested list\n * public Integer getInteger();\n *\n * // @return the nested list that this NestedInteger holds, if it holds a nested list\n * // Return empty list if this NestedInteger holds a single integer\n * public List getList();\n * }\n */\npublic class NestedIterator implements Iterator {\n\n public NestedIterator(List nestedList) {\n \n }\n\n @Override\n public Integer next() {\n \n }\n\n @Override\n public boolean hasNext() {\n \n }\n}\n\n/**\n * Your NestedIterator object will be instantiated and called as such:\n * NestedIterator i = new NestedIterator(nestedList);\n * while (i.hasNext()) v[f()] = i.next();\n */", "__typename": "CodeSnippetNode" }, { "lang": "Python", "langSlug": "python", "code": "# \"\"\"\n# This is the interface that allows for creating nested lists.\n# You should not implement it, or speculate about its implementation\n# \"\"\"\n#class NestedInteger(object):\n# def isInteger(self):\n# \"\"\"\n# @return True if this NestedInteger holds a single integer, rather than a nested list.\n# :rtype bool\n# \"\"\"\n#\n# def getInteger(self):\n# \"\"\"\n# @return the single integer that this NestedInteger holds, if it holds a single integer\n# Return None if this NestedInteger holds a nested list\n# :rtype int\n# \"\"\"\n#\n# def getList(self):\n# \"\"\"\n# @return the nested list that this NestedInteger holds, if it holds a nested list\n# Return None if this NestedInteger holds a single integer\n# :rtype List[NestedInteger]\n# \"\"\"\n\nclass NestedIterator(object):\n\n def __init__(self, nestedList):\n \"\"\"\n Initialize your data structure here.\n :type nestedList: List[NestedInteger]\n \"\"\"\n \n\n def next(self):\n \"\"\"\n :rtype: int\n \"\"\"\n \n\n def hasNext(self):\n \"\"\"\n :rtype: bool\n \"\"\"\n \n\n# Your NestedIterator object will be instantiated and called as such:\n# i, v = NestedIterator(nestedList), []\n# while i.hasNext(): v.append(i.next())", "__typename": "CodeSnippetNode" }, { "lang": "Python3", "langSlug": "python3", "code": "# \"\"\"\n# This is the interface that allows for creating nested lists.\n# You should not implement it, or speculate about its implementation\n# \"\"\"\n#class NestedInteger:\n# def isInteger(self) -> bool:\n# \"\"\"\n# @return True if this NestedInteger holds a single integer, rather than a nested list.\n# \"\"\"\n#\n# def getInteger(self) -> int:\n# \"\"\"\n# @return the single integer that this NestedInteger holds, if it holds a single integer\n# Return None if this NestedInteger holds a nested list\n# \"\"\"\n#\n# def getList(self) -> [NestedInteger]:\n# \"\"\"\n# @return the nested list that this NestedInteger holds, if it holds a nested list\n# Return None if this NestedInteger holds a single integer\n# \"\"\"\n\nclass NestedIterator:\n def __init__(self, nestedList: [NestedInteger]):\n \n \n def next(self) -> int:\n \n \n def hasNext(self) -> bool:\n \n\n# Your NestedIterator object will be instantiated and called as such:\n# i, v = NestedIterator(nestedList), []\n# while i.hasNext(): v.append(i.next())", "__typename": "CodeSnippetNode" }, { "lang": "C", "langSlug": "c", "code": "/**\n * *********************************************************************\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * *********************************************************************\n *\n * // Return true if this NestedInteger holds a single integer, rather than a nested list.\n * bool NestedIntegerIsInteger(struct NestedInteger *);\n *\n * // Return the single integer that this NestedInteger holds, if it holds a single integer\n * // The result is undefined if this NestedInteger holds a nested list\n * int NestedIntegerGetInteger(struct NestedInteger *);\n *\n * // Return the nested list that this NestedInteger holds, if it holds a nested list\n * // The result is undefined if this NestedInteger holds a single integer\n * struct NestedInteger **NestedIntegerGetList(struct NestedInteger *);\n *\n * // Return the nested list's size that this NestedInteger holds, if it holds a nested list\n * // The result is undefined if this NestedInteger holds a single integer\n * int NestedIntegerGetListSize(struct NestedInteger *);\n * };\n */\nstruct NestedIterator {\n \n};\n\nstruct NestedIterator *nestedIterCreate(struct NestedInteger** nestedList, int nestedListSize) {\n \n}\n\nbool nestedIterHasNext(struct NestedIterator *iter) {\n \n}\n\nint nestedIterNext(struct NestedIterator *iter) {\n \n}\n\n/** Deallocates memory previously allocated for the iterator */\nvoid nestedIterFree(struct NestedIterator *iter) {\n \n}\n\n/**\n * Your NestedIterator will be called like this:\n * struct NestedIterator *i = nestedIterCreate(nestedList, nestedListSize);\n * while (nestedIterHasNext(i)) printf(\"%d\\n\", nestedIterNext(i));\n * nestedIterFree(i);\n */", "__typename": "CodeSnippetNode" }, { "lang": "C#", "langSlug": "csharp", "code": "/**\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * interface NestedInteger {\n *\n * // @return true if this NestedInteger holds a single integer, rather than a nested list.\n * bool IsInteger();\n *\n * // @return the single integer that this NestedInteger holds, if it holds a single integer\n * // Return null if this NestedInteger holds a nested list\n * int GetInteger();\n *\n * // @return the nested list that this NestedInteger holds, if it holds a nested list\n * // Return null if this NestedInteger holds a single integer\n * IList GetList();\n * }\n */\npublic class NestedIterator {\n\n public NestedIterator(IList nestedList) {\n \n }\n\n public bool HasNext() {\n \n }\n\n public int Next() {\n \n }\n}\n\n/**\n * Your NestedIterator will be called like this:\n * NestedIterator i = new NestedIterator(nestedList);\n * while (i.HasNext()) v[f()] = i.Next();\n */", "__typename": "CodeSnippetNode" }, { "lang": "JavaScript", "langSlug": "javascript", "code": "/**\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * function NestedInteger() {\n *\n * Return true if this NestedInteger holds a single integer, rather than a nested list.\n * @return {boolean}\n * this.isInteger = function() {\n * ...\n * };\n *\n * Return the single integer that this NestedInteger holds, if it holds a single integer\n * Return null if this NestedInteger holds a nested list\n * @return {integer}\n * this.getInteger = function() {\n * ...\n * };\n *\n * Return the nested list that this NestedInteger holds, if it holds a nested list\n * Return null if this NestedInteger holds a single integer\n * @return {NestedInteger[]}\n * this.getList = function() {\n * ...\n * };\n * };\n */\n/**\n * @constructor\n * @param {NestedInteger[]} nestedList\n */\nvar NestedIterator = function(nestedList) {\n \n};\n\n\n/**\n * @this NestedIterator\n * @returns {boolean}\n */\nNestedIterator.prototype.hasNext = function() {\n \n};\n\n/**\n * @this NestedIterator\n * @returns {integer}\n */\nNestedIterator.prototype.next = function() {\n \n};\n\n/**\n * Your NestedIterator will be called like this:\n * var i = new NestedIterator(nestedList), a = [];\n * while (i.hasNext()) a.push(i.next());\n*/", "__typename": "CodeSnippetNode" }, { "lang": "TypeScript", "langSlug": "typescript", "code": "/**\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * class NestedInteger {\n * If value is provided, then it holds a single integer\n * Otherwise it holds an empty nested list\n * constructor(value?: number) {\n * ...\n * };\n *\n * Return true if this NestedInteger holds a single integer, rather than a nested list.\n * isInteger(): boolean {\n * ...\n * };\n *\n * Return the single integer that this NestedInteger holds, if it holds a single integer\n * Return null if this NestedInteger holds a nested list\n * getInteger(): number | null {\n * ...\n * };\n *\n * Set this NestedInteger to hold a single integer equal to value.\n * setInteger(value: number) {\n * ...\n * };\n *\n * Set this NestedInteger to hold a nested list and adds a nested integer elem to it.\n * add(elem: NestedInteger) {\n * ...\n * };\n *\n * Return the nested list that this NestedInteger holds,\n * or an empty list if this NestedInteger holds a single integer\n * getList(): NestedInteger[] {\n * ...\n * };\n * };\n */\n\nclass NestedIterator {\n constructor(nestedList: NestedInteger[]) {\n\t\t\n }\n\n hasNext(): boolean {\n\t\t\n }\n\n\tnext(): number {\n\t\t\n }\n}\n\n/**\n * Your ParkingSystem object will be instantiated and called as such:\n * var obj = new NestedIterator(nestedList)\n * var a: number[] = []\n * while (obj.hasNext()) a.push(obj.next());\n */", "__typename": "CodeSnippetNode" }, { "lang": "PHP", "langSlug": "php", "code": "/**\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * class NestedInteger {\n *\n * // if value is not specified, initializes an empty list.\n * // Otherwise initializes a single integer equal to value.\n * function __construct($value = null)\n *\n * // Return true if this NestedInteger holds a single integer, rather than a nested list.\n * function isInteger() : bool\n *\n * // Return the single integer that this NestedInteger holds, if it holds a single integer\n * // The result is undefined if this NestedInteger holds a nested list\n * function getInteger()\n *\n * // Set this NestedInteger to hold a single integer.\n * function setInteger($i) : void\n *\n * // Set this NestedInteger to hold a nested list and adds a nested integer to it.\n * function add($ni) : void\n *\n * // Return the nested list that this NestedInteger holds, if it holds a nested list\n * // The result is undefined if this NestedInteger holds a single integer\n * function getList() : array\n * }\n */\n\nclass NestedIterator {\n /**\n * @param NestedInteger[] $nestedList\n */\n function __construct($nestedList) {\n \n }\n \n /**\n * @return Integer\n */\n function next() {\n \n }\n \n /**\n * @return Boolean\n */\n function hasNext() {\n \n }\n}\n\n/**\n * Your NestedIterator object will be instantiated and called as such:\n * $obj = NestedIterator($nestedList);\n * $ret_1 = $obj->next();\n * $ret_2 = $obj->hasNext();\n */", "__typename": "CodeSnippetNode" }, { "lang": "Swift", "langSlug": "swift", "code": "/**\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * class NestedInteger {\n * // Return true if this NestedInteger holds a single integer, rather than a nested list.\n * public func isInteger() -> Bool\n *\n * // Return the single integer that this NestedInteger holds, if it holds a single integer\n * // The result is undefined if this NestedInteger holds a nested list\n * public func getInteger() -> Int\n *\n * // Set this NestedInteger to hold a single integer.\n * public func setInteger(value: Int)\n *\n * // Set this NestedInteger to hold a nested list and adds a nested integer to it.\n * public func add(elem: NestedInteger)\n *\n * // Return the nested list that this NestedInteger holds, if it holds a nested list\n * // The result is undefined if this NestedInteger holds a single integer\n * public func getList() -> [NestedInteger]\n * }\n */\n\nclass NestedIterator {\n\n init(_ nestedList: [NestedInteger]) {\n \n }\n \n func next() -> Int {\n \n }\n \n func hasNext() -> Bool {\n \n }\n}\n\n/**\n * Your NestedIterator object will be instantiated and called as such:\n * let obj = NestedIterator(nestedList)\n * let ret_1: Int = obj.next()\n * let ret_2: Bool = obj.hasNext()\n */", "__typename": "CodeSnippetNode" }, { "lang": "Kotlin", "langSlug": "kotlin", "code": "/**\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * class NestedInteger {\n * // Constructor initializes an empty nested list.\n * constructor()\n *\n * // Constructor initializes a single integer.\n * constructor(value: Int)\n *\n * // @return true if this NestedInteger holds a single integer, rather than a nested list.\n * fun isInteger(): Boolean\n *\n * // @return the single integer that this NestedInteger holds, if it holds a single integer\n * // Return null if this NestedInteger holds a nested list\n * fun getInteger(): Int?\n *\n * // Set this NestedInteger to hold a single integer.\n * fun setInteger(value: Int): Unit\n *\n * // Set this NestedInteger to hold a nested list and adds a nested integer to it.\n * fun add(ni: NestedInteger): Unit\n *\n * // @return the nested list that this NestedInteger holds, if it holds a nested list\n * // Return null if this NestedInteger holds a single integer\n * fun getList(): List?\n * }\n */\n\nclass NestedIterator(nestedList: List) {\n fun next(): Int {\n \n }\n \n fun hasNext(): Boolean {\n \n }\n}\n\n/**\n * Your NestedIterator object will be instantiated and called as such:\n * var obj = NestedIterator(nestedList)\n * var param_1 = obj.next()\n * var param_2 = obj.hasNext()\n */", "__typename": "CodeSnippetNode" }, { "lang": "Go", "langSlug": "golang", "code": "/**\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * type NestedInteger struct {\n * }\n *\n * // Return true if this NestedInteger holds a single integer, rather than a nested list.\n * func (this NestedInteger) IsInteger() bool {}\n *\n * // Return the single integer that this NestedInteger holds, if it holds a single integer\n * // The result is undefined if this NestedInteger holds a nested list\n * // So before calling this method, you should have a check\n * func (this NestedInteger) GetInteger() int {}\n *\n * // Set this NestedInteger to hold a single integer.\n * func (n *NestedInteger) SetInteger(value int) {}\n *\n * // Set this NestedInteger to hold a nested list and adds a nested integer to it.\n * func (this *NestedInteger) Add(elem NestedInteger) {}\n *\n * // Return the nested list that this NestedInteger holds, if it holds a nested list\n * // The list length is zero if this NestedInteger holds a single integer\n * // You can access NestedInteger's List element directly if you want to modify it\n * func (this NestedInteger) GetList() []*NestedInteger {}\n */\n\ntype NestedIterator struct {\n \n}\n\nfunc Constructor(nestedList []*NestedInteger) *NestedIterator {\n \n}\n\nfunc (this *NestedIterator) Next() int {\n \n}\n\nfunc (this *NestedIterator) HasNext() bool {\n \n}", "__typename": "CodeSnippetNode" }, { "lang": "Ruby", "langSlug": "ruby", "code": "# This is the interface that allows for creating nested lists.\n# You should not implement it, or speculate about its implementation\n#\n#class NestedInteger\n# def is_integer()\n# \"\"\"\n# Return true if this NestedInteger holds a single integer, rather than a nested list.\n# @return {Boolean}\n# \"\"\"\n#\n# def get_integer()\n# \"\"\"\n# Return the single integer that this NestedInteger holds, if it holds a single integer\n# Return nil if this NestedInteger holds a nested list\n# @return {Integer}\n# \"\"\"\n#\n# def get_list()\n# \"\"\"\n# Return the nested list that this NestedInteger holds, if it holds a nested list\n# Return nil if this NestedInteger holds a single integer\n# @return {NestedInteger[]}\n# \"\"\"\n\nclass NestedIterator\n # @param {NestedInteger[]} nested_list\n def initialize(nested_list)\n \n end\n\n # @return {Boolean}\n def has_next\n \n end\n\n # @return {Integer}\n def next\n \n end\nend\n\n# Your NestedIterator will be called like this:\n# i, v = NestedIterator.new(nested_list), []\n# while i.has_next()\n# v << i.next\n# end", "__typename": "CodeSnippetNode" }, { "lang": "Scala", "langSlug": "scala", "code": "/**\n * // This is the interface that allows for creating nested lists.\n * // You should not implement it, or speculate about its implementation\n * trait NestedInteger {\n *\n * // Return true if this NestedInteger holds a single integer, rather than a nested list.\n * def isInteger: Boolean\n *\n * // Return the single integer that this NestedInteger holds, if it holds a single integer.\n * def getInteger: Int\n *\n * // Set this NestedInteger to hold a single integer.\n * def setInteger(i: Int): Unit\n *\n * // Return the nested list that this NestedInteger holds, if it holds a nested list.\n * def getList: Array[NestedInteger]\n *\n * // Set this NestedInteger to hold a nested list and adds a nested integer to it.\n * def add(ni: NestedInteger): Unit\n * }\n */\n\nclass NestedIterator(_nestedList: List[NestedInteger]) {\n def next(): Int = {\n \n }\n \n def hasNext(): Boolean = {\n \n }\n}\n\n/**\n * Your NestedIterator object will be instantiated and called as such:\n * var obj = new NestedIterator(nestedList)\n * var param_1 = obj.next()\n * var param_2 = obj.hasNext()\n */", "__typename": "CodeSnippetNode" }, { "lang": "Rust", "langSlug": "rust", "code": "// #[derive(Debug, PartialEq, Eq)]\n// pub enum NestedInteger {\n// Int(i32),\n// List(Vec)\n// }\nstruct NestedIterator {\n\n}\n\n\n/** \n * `&self` means the method takes an immutable reference.\n * If you need a mutable reference, change it to `&mut self` instead.\n */\nimpl NestedIterator {\n\n fn new(nestedList: Vec) -> Self {\n \n }\n \n fn next(&self) -> i32 {\n \n }\n \n fn has_next(&self) -> bool {\n \n }\n}\n\n/**\n * Your NestedIterator object will be instantiated and called as such:\n * let obj = NestedIterator::new(nestedList);\n * let ret_1: i32 = obj.next();\n * let ret_2: bool = obj.has_next();\n */", "__typename": 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\\r\\n

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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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Go 1.21

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Supports rand v0.6\\u00a0from crates.io

\"], \"php\": [\"PHP\", \"

PHP 8.1.

\\r\\n

With bcmath module

\"], \"typescript\": [\"Typescript\", \"

TypeScript 5.1.6, Node.js 16.13.2.

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

Your code is run with --harmony flag, enabling new ES2022 features.

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

lodash.js library is included by default.

\"]}", "libraryUrl": null, "adminUrl": null, "challengeQuestion": { "id": "1521", "date": "2023-10-20", "incompleteChallengeCount": 0, "streakCount": 0, "type": "DAILY", "__typename": "ChallengeQuestionNode" }, "__typename": "QuestionNode" } } }