{"id":3193,"date":"2021-06-12T08:10:30","date_gmt":"2021-06-12T02:40:30","guid":{"rendered":"https:\/\/www.codingbroz.com\/?p=3193"},"modified":"2022-07-01T20:58:55","modified_gmt":"2022-07-01T15:28:55","slug":"how-to-implement-a-queue-using-linked-list","status":"publish","type":"post","link":"https:\/\/www.codingbroz.com\/how-to-implement-a-queue-using-linked-list\/","title":{"rendered":"How to implement a queue using linked list &#8211; Java &#038; C++"},"content":{"rendered":"\n<p>Hello Coders! Welcome to codingbroz and our Data Structures and algorithm interview series.<\/p>\n\n\n\n<p>Today, we are going to see an interesting problem commonly asked in coding interviews is <strong>How to implement a queue using linked list<\/strong>? We will also implement the code in Java as well as C++ programming language.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1200\" height=\"686\" src=\"https:\/\/www.codingbroz.com\/wp-content\/uploads\/2021\/06\/queue-linkedlist.png\" alt=\"How to implement a queue using linked list\" class=\"wp-image-3194\" srcset=\"https:\/\/www.codingbroz.com\/wp-content\/uploads\/2021\/06\/queue-linkedlist.png 1200w, https:\/\/www.codingbroz.com\/wp-content\/uploads\/2021\/06\/queue-linkedlist-768x439.png 768w\" sizes=\"(max-width: 1200px) 100vw, 1200px\" \/><\/figure>\n\n\n\n<p><strong>Also Read : <\/strong><em><a href=\"https:\/\/www.codingbroz.com\/how-to-implement-a-stack-using-linked-list\/\" target=\"_blank\" data-type=\"URL\" data-id=\"https:\/\/www.codingbroz.com\/how-to-implement-a-stack-using-linked-list\/\" rel=\"noreferrer noopener\">How to implement a stack using linked list &#8211; Java &amp; C++<\/a><\/em><\/p>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_66_1 ez-toc-wrap-left counter-hierarchy ez-toc-counter ez-toc-custom ez-toc-container-direction\">\n<label for=\"ez-toc-cssicon-toggle-item-6645c1a98cd44\" class=\"ez-toc-cssicon-toggle-label\"><label class=\"ez-toc-title\">Table of Contents<\/label>\n<span class=\"ez-toc-cssicon\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #0090ff;color:#0090ff\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #0090ff;color:#0090ff\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/label><input type=\"checkbox\"  id=\"ez-toc-cssicon-toggle-item-6645c1a98cd44\" checked \/><nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.codingbroz.com\/how-to-implement-a-queue-using-linked-list\/#Problem\" title=\"Problem\">Problem<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.codingbroz.com\/how-to-implement-a-queue-using-linked-list\/#Solution_%E2%80%93_How_to_implement_a_queue_using_linked_list\" title=\"Solution &#8211; How to implement a queue using linked list\">Solution &#8211; How to implement a queue using linked list<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.codingbroz.com\/how-to-implement-a-queue-using-linked-list\/#Java\" title=\"Java\">Java<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.codingbroz.com\/how-to-implement-a-queue-using-linked-list\/#C\" title=\"C++\">C++<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Problem\"><\/span><strong>Problem<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>The problem statement says that you have to implement a queue using linked list. <\/p>\n\n\n\n<p>You have to implement the FIFO property of the queue data structure using the linked list data structure.<\/p>\n\n\n\n<p>You have to implement the following functions using a linked list which follows the FIFO property of queue :<\/p>\n\n\n\n<ul><li><strong>enqueue() \/ add() : <\/strong>This function should accept data in FIFO manner.<\/li><li><strong>dequeue() \/ remove() : <\/strong>This function should return and remove data in FIFO manner.<\/li><li><strong>peek() : <\/strong>This function should return the data in FIFO manner.<\/li><\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Solution_%E2%80%93_How_to_implement_a_queue_using_linked_list\"><\/span><strong>Solution &#8211; How to implement a queue using linked list<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Java\"><\/span><strong>Java<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"java\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">import java.io.*;\nimport java.util.*;\n\npublic class Main {\n\n  public static class LLToQueueAdapter {\n    LinkedList&lt;Integer> list;\n\n    public LLToQueueAdapter() {\n      list = new LinkedList&lt;>();\n    }\n\n    int size() {\n      return list.size();\n    }\n\n    void add(int val) {\n      list.addLast(val);\n    }\n\n    int remove() {\n      if(size()==0){\n          System.out.println(\"Queue underflow\");\n          return -1;\n      }\n      else{\n          return list.removeFirst();\n      }\n    }\n\n    int peek() {\n        if(size()==0){\n          System.out.println(\"Queue underflow\");\n          return -1;\n      }\n      else{\n          return list.getFirst();\n      }\n    }\n  }\n\n  public static void main(String[] args) throws Exception {\n    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));\n    LLToQueueAdapter qu = new LLToQueueAdapter();\n\n    String str = br.readLine();\n    while (str.equals(\"quit\") == false) {\n      if (str.startsWith(\"add\")) {\n        int val = Integer.parseInt(str.split(\" \")[1]);\n        qu.add(val);\n      } else if (str.startsWith(\"remove\")) {\n        int val = qu.remove();\n        if (val != -1) {\n          System.out.println(val);\n        }\n      } else if (str.startsWith(\"peek\")) {\n        int val = qu.peek();\n        if (val != -1) {\n          System.out.println(val);\n        }\n      } else if (str.startsWith(\"size\")) {\n        System.out.println(qu.size());\n      }\n      str = br.readLine();\n    }\n  }\n}\n\n<\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C\"><\/span><strong>C++<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"cpp\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">#include &lt;iostream>\n#include &lt;list>\nusing namespace std;\n\/\/ Add an element to the tail of the linked list\nvoid enqueue(int elem, list &lt;int> &amp;Queue){\n   Queue.push_back(elem);\n}\n\/\/ Remove an element from the head of the linked list\nint dequeue(list &lt;int> &amp;Queue){\n  if(!Queue.empty()){\n    int temp = Queue.front();\n    Queue.pop_front();\n    return temp;\n  }\n}\n\/\/ Display the element from the tail of the linked list\nint peek(list &lt;int> &amp;Queue){\n  if(!Queue.empty()){\n    return Queue.back();\n  }\n}\nint main() {\n  \/\/ Declaring a list to be used as a Queue\n  list &lt;int> Queue;\n  \/\/ Enqueue 3\n  enqueue(3, Queue);\n  \/\/ Display element at the tail of the linked list\n  cout&lt;&lt;\"Element at tail: \"&lt;&lt;peek(Queue)&lt;&lt;endl;\n  \/\/ Enqueue 4\n  enqueue(4, Queue);\n  \/\/ Display element at the tail of the linked list\n  cout&lt;&lt;\"Element at tail: \"&lt;&lt;peek(Queue)&lt;&lt;endl;\n  \/\/ Enqueue 5\n  enqueue(5, Queue);\n  \/\/ Display element at the tail of the linked list\n  cout&lt;&lt;\"Element at tail: \"&lt;&lt;peek(Queue)&lt;&lt;endl;\n  \/\/ Dequeue elements\n  cout&lt;&lt;\"Element dequeued: \"&lt;&lt;dequeue(Queue)&lt;&lt;endl;\n  cout&lt;&lt;\"Element dequeued: \"&lt;&lt;dequeue(Queue)&lt;&lt;endl;\n  cout&lt;&lt;\"Element dequeued: \"&lt;&lt;dequeue(Queue)&lt;&lt;endl;\n  return 0;\n}\n\n<\/pre>\n\n\n\n<p>To<strong> Practice more<\/strong> <strong><a href=\"https:\/\/www.codingbroz.com\/top-interview-preparation-questions-for-product-based-companies\/\" target=\"_blank\" data-type=\"URL\" data-id=\"https:\/\/www.codingbroz.com\/top-interview-preparation-questions-for-product-based-companies\/\" rel=\"noreferrer noopener\">Interview Questions<\/a><\/strong>, <strong>Checkout<\/strong> other articles too on <a href=\"https:\/\/www.codingbroz.com\" target=\"_blank\" data-type=\"URL\" data-id=\"www.www.codingbroz.com\" rel=\"noreferrer noopener\">CodingBroz<\/a> \ud83d\ude42<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Hello Coders! Welcome to codingbroz and our Data Structures and algorithm interview series.<br \/>\nToday, we are going to see an interesting problem commonly asked in coding interviews is How to implement a queue using linked list ? We will also implement the code in Java as well as C++ programming language.<\/p>\n","protected":false},"author":3,"featured_media":3194,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"default","ast-site-content-layout":"","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"default","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""}},"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[128],"tags":[122,116,113,196],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/www.codingbroz.com\/wp-content\/uploads\/2021\/06\/queue-linkedlist.png","jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/posts\/3193"}],"collection":[{"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/comments?post=3193"}],"version-history":[{"count":2,"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/posts\/3193\/revisions"}],"predecessor-version":[{"id":3196,"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/posts\/3193\/revisions\/3196"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/media\/3194"}],"wp:attachment":[{"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/media?parent=3193"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/categories?post=3193"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.codingbroz.com\/wp-json\/wp\/v2\/tags?post=3193"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}