{ "data": { "question": { "questionId": "232", "questionFrontendId": "232", "boundTopicId": null, "title": "Implement Queue using Stacks", "titleSlug": "implement-queue-using-stacks", "content": "

Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push, peek, pop, and empty).

\n\n

Implement the MyQueue class:

\n\n\n\n

Notes:

\n\n\n\n

 

\n

Example 1:

\n\n
\nInput\n["MyQueue", "push", "push", "peek", "pop", "empty"]\n[[], [1], [2], [], [], []]\nOutput\n[null, null, null, 1, 1, false]\n\nExplanation\nMyQueue myQueue = new MyQueue();\nmyQueue.push(1); // queue is: [1]\nmyQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue)\nmyQueue.peek(); // return 1\nmyQueue.pop(); // return 1, queue is [2]\nmyQueue.empty(); // return false\n
\n\n

 

\n

Constraints:

\n\n\n\n

 

\n

Follow-up: Can you implement the queue such that each operation is amortized O(1) time complexity? In other words, performing n operations will take overall O(n) time even if one of those operations may take longer.

\n", "translatedTitle": null, "translatedContent": null, "isPaidOnly": false, "difficulty": "Easy", "likes": 6856, "dislikes": 389, "isLiked": null, "similarQuestions": "[{\"title\": \"Implement Stack using Queues\", \"titleSlug\": \"implement-stack-using-queues\", \"difficulty\": \"Easy\", \"translatedTitle\": null}]", "exampleTestcases": "[\"MyQueue\",\"push\",\"push\",\"peek\",\"pop\",\"empty\"]\n[[],[1],[2],[],[],[]]", "categoryTitle": "Algorithms", "contributors": [], "topicTags": [ { "name": "Stack", "slug": "stack", "translatedName": null, "__typename": "TopicTagNode" }, { "name": "Design", "slug": "design", "translatedName": null, "__typename": "TopicTagNode" }, { "name": "Queue", "slug": "queue", "translatedName": null, "__typename": "TopicTagNode" } ], "companyTagStats": null, "codeSnippets": [ { "lang": "C++", "langSlug": "cpp", "code": "class MyQueue {\npublic:\n MyQueue() {\n \n }\n \n void push(int x) {\n \n }\n \n int pop() {\n \n }\n \n int peek() {\n \n }\n \n bool empty() {\n \n }\n};\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * MyQueue* obj = new MyQueue();\n * obj->push(x);\n * int param_2 = obj->pop();\n * int param_3 = obj->peek();\n * bool param_4 = obj->empty();\n */", "__typename": "CodeSnippetNode" }, { "lang": "Java", "langSlug": "java", "code": "class MyQueue {\n\n public MyQueue() {\n \n }\n \n public void push(int x) {\n \n }\n \n public int pop() {\n \n }\n \n public int peek() {\n \n }\n \n public boolean empty() {\n \n }\n}\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * MyQueue obj = new MyQueue();\n * obj.push(x);\n * int param_2 = obj.pop();\n * int param_3 = obj.peek();\n * boolean param_4 = obj.empty();\n */", "__typename": "CodeSnippetNode" }, { "lang": "Python", "langSlug": "python", "code": "class MyQueue(object):\n\n def __init__(self):\n \n\n def push(self, x):\n \"\"\"\n :type x: int\n :rtype: None\n \"\"\"\n \n\n def pop(self):\n \"\"\"\n :rtype: int\n \"\"\"\n \n\n def peek(self):\n \"\"\"\n :rtype: int\n \"\"\"\n \n\n def empty(self):\n \"\"\"\n :rtype: bool\n \"\"\"\n \n\n\n# Your MyQueue object will be instantiated and called as such:\n# obj = MyQueue()\n# obj.push(x)\n# param_2 = obj.pop()\n# param_3 = obj.peek()\n# param_4 = obj.empty()", "__typename": "CodeSnippetNode" }, { "lang": "Python3", "langSlug": "python3", "code": "class MyQueue:\n\n def __init__(self):\n \n\n def push(self, x: int) -> None:\n \n\n def pop(self) -> int:\n \n\n def peek(self) -> int:\n \n\n def empty(self) -> bool:\n \n\n\n# Your MyQueue object will be instantiated and called as such:\n# obj = MyQueue()\n# obj.push(x)\n# param_2 = obj.pop()\n# param_3 = obj.peek()\n# param_4 = obj.empty()", "__typename": "CodeSnippetNode" }, { "lang": "C", "langSlug": "c", "code": "\n\n\ntypedef struct {\n \n} MyQueue;\n\n\nMyQueue* myQueueCreate() {\n \n}\n\nvoid myQueuePush(MyQueue* obj, int x) {\n \n}\n\nint myQueuePop(MyQueue* obj) {\n \n}\n\nint myQueuePeek(MyQueue* obj) {\n \n}\n\nbool myQueueEmpty(MyQueue* obj) {\n \n}\n\nvoid myQueueFree(MyQueue* obj) {\n \n}\n\n/**\n * Your MyQueue struct will be instantiated and called as such:\n * MyQueue* obj = myQueueCreate();\n * myQueuePush(obj, x);\n \n * int param_2 = myQueuePop(obj);\n \n * int param_3 = myQueuePeek(obj);\n \n * bool param_4 = myQueueEmpty(obj);\n \n * myQueueFree(obj);\n*/", "__typename": "CodeSnippetNode" }, { "lang": "C#", "langSlug": "csharp", "code": "public class MyQueue {\n\n public MyQueue() {\n \n }\n \n public void Push(int x) {\n \n }\n \n public int Pop() {\n \n }\n \n public int Peek() {\n \n }\n \n public bool Empty() {\n \n }\n}\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * MyQueue obj = new MyQueue();\n * obj.Push(x);\n * int param_2 = obj.Pop();\n * int param_3 = obj.Peek();\n * bool param_4 = obj.Empty();\n */", "__typename": "CodeSnippetNode" }, { "lang": "JavaScript", "langSlug": "javascript", "code": "\nvar MyQueue = function() {\n \n};\n\n/** \n * @param {number} x\n * @return {void}\n */\nMyQueue.prototype.push = function(x) {\n \n};\n\n/**\n * @return {number}\n */\nMyQueue.prototype.pop = function() {\n \n};\n\n/**\n * @return {number}\n */\nMyQueue.prototype.peek = function() {\n \n};\n\n/**\n * @return {boolean}\n */\nMyQueue.prototype.empty = function() {\n \n};\n\n/** \n * Your MyQueue object will be instantiated and called as such:\n * var obj = new MyQueue()\n * obj.push(x)\n * var param_2 = obj.pop()\n * var param_3 = obj.peek()\n * var param_4 = obj.empty()\n */", "__typename": "CodeSnippetNode" }, { "lang": "TypeScript", "langSlug": "typescript", "code": "class MyQueue {\n constructor() {\n \n }\n\n push(x: number): void {\n \n }\n\n pop(): number {\n \n }\n\n peek(): number {\n \n }\n\n empty(): boolean {\n \n }\n}\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * var obj = new MyQueue()\n * obj.push(x)\n * var param_2 = obj.pop()\n * var param_3 = obj.peek()\n * var param_4 = obj.empty()\n */", "__typename": "CodeSnippetNode" }, { "lang": "PHP", "langSlug": "php", "code": "class MyQueue {\n /**\n */\n function __construct() {\n \n }\n \n /**\n * @param Integer $x\n * @return NULL\n */\n function push($x) {\n \n }\n \n /**\n * @return Integer\n */\n function pop() {\n \n }\n \n /**\n * @return Integer\n */\n function peek() {\n \n }\n \n /**\n * @return Boolean\n */\n function empty() {\n \n }\n}\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * $obj = MyQueue();\n * $obj->push($x);\n * $ret_2 = $obj->pop();\n * $ret_3 = $obj->peek();\n * $ret_4 = $obj->empty();\n */", "__typename": "CodeSnippetNode" }, { "lang": "Swift", "langSlug": "swift", "code": "\nclass MyQueue {\n\n init() {\n \n }\n \n func push(_ x: Int) {\n \n }\n \n func pop() -> Int {\n \n }\n \n func peek() -> Int {\n \n }\n \n func empty() -> Bool {\n \n }\n}\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * let obj = MyQueue()\n * obj.push(x)\n * let ret_2: Int = obj.pop()\n * let ret_3: Int = obj.peek()\n * let ret_4: Bool = obj.empty()\n */", "__typename": "CodeSnippetNode" }, { "lang": "Kotlin", "langSlug": "kotlin", "code": "class MyQueue() {\n\n fun push(x: Int) {\n \n }\n\n fun pop(): Int {\n \n }\n\n fun peek(): Int {\n \n }\n\n fun empty(): Boolean {\n \n }\n\n}\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * var obj = MyQueue()\n * obj.push(x)\n * var param_2 = obj.pop()\n * var param_3 = obj.peek()\n * var param_4 = obj.empty()\n */", "__typename": "CodeSnippetNode" }, { "lang": "Dart", "langSlug": "dart", "code": "class MyQueue {\n\n MyQueue() {\n \n }\n \n void push(int x) {\n \n }\n \n int pop() {\n \n }\n \n int peek() {\n \n }\n \n bool empty() {\n \n }\n}\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * MyQueue obj = MyQueue();\n * obj.push(x);\n * int param2 = obj.pop();\n * int param3 = obj.peek();\n * bool param4 = obj.empty();\n */", "__typename": "CodeSnippetNode" }, { "lang": "Go", "langSlug": "golang", "code": "type MyQueue struct {\n \n}\n\n\nfunc Constructor() MyQueue {\n \n}\n\n\nfunc (this *MyQueue) Push(x int) {\n \n}\n\n\nfunc (this *MyQueue) Pop() int {\n \n}\n\n\nfunc (this *MyQueue) Peek() int {\n \n}\n\n\nfunc (this *MyQueue) Empty() bool {\n \n}\n\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * obj := Constructor();\n * obj.Push(x);\n * param_2 := obj.Pop();\n * param_3 := obj.Peek();\n * param_4 := obj.Empty();\n */", "__typename": "CodeSnippetNode" }, { "lang": "Ruby", "langSlug": "ruby", "code": "class MyQueue\n def initialize()\n \n end\n\n\n=begin\n :type x: Integer\n :rtype: Void\n=end\n def push(x)\n \n end\n\n\n=begin\n :rtype: Integer\n=end\n def pop()\n \n end\n\n\n=begin\n :rtype: Integer\n=end\n def peek()\n \n end\n\n\n=begin\n :rtype: Boolean\n=end\n def empty()\n \n end\n\n\nend\n\n# Your MyQueue object will be instantiated and called as such:\n# obj = MyQueue.new()\n# obj.push(x)\n# param_2 = obj.pop()\n# param_3 = obj.peek()\n# param_4 = obj.empty()", "__typename": "CodeSnippetNode" }, { "lang": "Scala", "langSlug": "scala", "code": "class MyQueue() {\n\n def push(x: Int) {\n \n }\n\n def pop(): Int = {\n \n }\n\n def peek(): Int = {\n \n }\n\n def empty(): Boolean = {\n \n }\n\n}\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * var obj = new MyQueue()\n * obj.push(x)\n * var param_2 = obj.pop()\n * var param_3 = obj.peek()\n * var param_4 = obj.empty()\n */", "__typename": "CodeSnippetNode" }, { "lang": "Rust", "langSlug": "rust", "code": "struct MyQueue {\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 MyQueue {\n\n fn new() -> Self {\n \n }\n \n fn push(&self, x: i32) {\n \n }\n \n fn pop(&self) -> i32 {\n \n }\n \n fn peek(&self) -> i32 {\n \n }\n \n fn empty(&self) -> bool {\n \n }\n}\n\n/**\n * Your MyQueue object will be instantiated and called as such:\n * let obj = MyQueue::new();\n * obj.push(x);\n * let ret_2: i32 = obj.pop();\n * let ret_3: i32 = obj.peek();\n * let ret_4: bool = obj.empty();\n */", "__typename": "CodeSnippetNode" }, { "lang": "Racket", "langSlug": "racket", "code": "(define my-queue%\n (class object%\n (super-new)\n \n (init-field)\n \n ; push : exact-integer? -> void?\n (define/public (push x)\n )\n ; pop : -> exact-integer?\n (define/public (pop)\n )\n ; peek : -> exact-integer?\n (define/public (peek)\n )\n ; empty : -> boolean?\n (define/public (empty)\n )))\n\n;; Your my-queue% object will be instantiated and called as such:\n;; (define obj (new my-queue%))\n;; (send obj push x)\n;; (define param_2 (send obj pop))\n;; (define param_3 (send obj peek))\n;; (define param_4 (send obj empty))", "__typename": "CodeSnippetNode" }, { "lang": "Erlang", "langSlug": "erlang", "code": "-spec my_queue_init_() -> any().\nmy_queue_init_() ->\n .\n\n-spec my_queue_push(X :: integer()) -> any().\nmy_queue_push(X) ->\n .\n\n-spec my_queue_pop() -> integer().\nmy_queue_pop() ->\n .\n\n-spec my_queue_peek() -> integer().\nmy_queue_peek() ->\n .\n\n-spec my_queue_empty() -> boolean().\nmy_queue_empty() ->\n .\n\n\n%% Your functions will be called as such:\n%% my_queue_init_(),\n%% my_queue_push(X),\n%% Param_2 = my_queue_pop(),\n%% Param_3 = my_queue_peek(),\n%% Param_4 = my_queue_empty(),\n\n%% my_queue_init_ will be called before every test case, in which you can do some necessary initializations.", "__typename": "CodeSnippetNode" }, { "lang": "Elixir", "langSlug": "elixir", "code": "defmodule MyQueue do\n @spec init_() :: any\n def init_() do\n \n end\n\n @spec push(x :: integer) :: any\n def push(x) do\n \n end\n\n @spec pop() :: integer\n def pop() do\n \n end\n\n @spec peek() :: integer\n def peek() do\n \n end\n\n @spec empty() :: boolean\n def empty() do\n \n end\nend\n\n# Your functions will be called as such:\n# MyQueue.init_()\n# MyQueue.push(x)\n# param_2 = MyQueue.pop()\n# param_3 = MyQueue.peek()\n# param_4 = MyQueue.empty()\n\n# MyQueue.init_ will be called before every test case, in which you can do some necessary initializations.", "__typename": "CodeSnippetNode" } ], "stats": "{\"totalAccepted\": \"761.5K\", \"totalSubmission\": \"1.2M\", \"totalAcceptedRaw\": 761461, \"totalSubmissionRaw\": 1185373, \"acRate\": \"64.2%\"}", "hints": [], "solution": { "id": "47", "canSeeDetail": true, "paidOnly": false, "hasVideoSolution": false, "paidOnlyVideo": true, "__typename": "ArticleNode" }, "status": null, "sampleTestCase": "[\"MyQueue\",\"push\",\"push\",\"peek\",\"pop\",\"empty\"]\n[[],[1],[2],[],[],[]]", "metaData": "{\n \"classname\": \"MyQueue\",\n \"constructor\": {\n \"params\": []\n },\n \"methods\": [\n {\n \"params\": [\n {\n \"type\": \"integer\",\n \"name\": \"x\"\n }\n ],\n \"return\": {\n \"type\": \"void\"\n },\n \"name\": \"push\"\n },\n {\n \"params\": [],\n \"return\": {\n \"type\": \"integer\"\n },\n \"name\": \"pop\"\n },\n {\n \"params\": [],\n \"return\": {\n \"type\": \"integer\"\n },\n \"name\": \"peek\"\n },\n {\n \"params\": [],\n \"return\": {\n \"type\": \"boolean\"\n },\n \"name\": \"empty\"\n }\n ],\n \"return\": {\n \"type\": \"boolean\"\n },\n \"systemdesign\": 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.

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

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

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

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

\"], \"java\": [\"Java\", \"

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

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

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

\\r\\n

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

\"], \"python\": [\"Python\", \"

Python 2.7.12.

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

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

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

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

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

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

\"], \"c\": [\"C\", \"

Compiled with gcc 8.2 using the gnu11 standard.

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

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

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

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

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

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

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

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

\\r\\nstruct hash_entry {\\r\\n    int id;            /* we'll use this field as the key */\\r\\n    char name[10];\\r\\n    UT_hash_handle hh; /* makes this structure hashable */\\r\\n};\\r\\n\\r\\nstruct hash_entry *users = NULL;\\r\\n\\r\\nvoid add_user(struct hash_entry *s) {\\r\\n    HASH_ADD_INT(users, id, s);\\r\\n}\\r\\n
\\r\\n

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

2. Looking up an item in a hash:\\r\\n

\\r\\nstruct hash_entry *find_user(int user_id) {\\r\\n    struct hash_entry *s;\\r\\n    HASH_FIND_INT(users, &user_id, s);\\r\\n    return s;\\r\\n}\\r\\n
\\r\\n

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

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

\\r\\nvoid delete_user(struct hash_entry *user) {\\r\\n    HASH_DEL(users, user);  \\r\\n}\\r\\n
\\r\\n

\"], \"csharp\": [\"C#\", \"

C# 10 with .NET 6 runtime

\"], \"javascript\": [\"JavaScript\", \"

Node.js 16.13.2.

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

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

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

lodash.js library is included by default.

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

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.

\"], \"ruby\": [\"Ruby\", \"

Ruby 3.1

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

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

\"], \"swift\": [\"Swift\", \"

Swift 5.5.2.

\"], \"golang\": [\"Go\", \"

Go 1.21

\\r\\n

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

\"], \"python3\": [\"Python3\", \"

Python 3.10.

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

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

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

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

\"], \"scala\": [\"Scala\", \"

Scala 2.13.7.

\"], \"kotlin\": [\"Kotlin\", \"

Kotlin 1.9.0.

\"], \"rust\": [\"Rust\", \"

Rust 1.58.1

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

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.

\"], \"racket\": [\"Racket\", \"

Run with Racket 8.3.

\"], \"erlang\": [\"Erlang\", \"Erlang/OTP 25.0\"], \"elixir\": [\"Elixir\", \"Elixir 1.13.4 with Erlang/OTP 25.0\"], \"dart\": [\"Dart\", \"

Dart 2.17.3

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

Your code will be run directly without compiling

\"]}", "libraryUrl": null, "adminUrl": null, "challengeQuestion": null, "__typename": "QuestionNode" } } }