{"id":9239,"date":"2025-08-12T15:00:37","date_gmt":"2025-08-12T09:30:37","guid":{"rendered":"https:\/\/namastedev.com\/blog\/?p=9239"},"modified":"2025-10-15T18:05:27","modified_gmt":"2025-10-15T12:35:27","slug":"priority-queues-introduction","status":"publish","type":"post","link":"https:\/\/namastedev.com\/blog\/priority-queues-introduction\/","title":{"rendered":"Priority Queues Introduction"},"content":{"rendered":"\n\n<!-- Priority: 8 -->\n<!-- Prism.js for Code Highlighting -->\n<link\n    href=\"https:\/\/cdn.jsdelivr.net\/npm\/prismjs@1.29.0\/themes\/prism-tomorrow.min.css\"\n    rel=\"stylesheet\"\n\/>\n<script src=\"https:\/\/cdn.jsdelivr.net\/npm\/prismjs@1.29.0\/prism.min.js\"><\/script>\n<script src=\"https:\/\/cdn.jsdelivr.net\/npm\/prismjs@1.29.0\/plugins\/autoloader\/prism-autoloader.min.js\"><\/script>\n\n<style>\n.wp_blog_theme {\n  --primary: #E58C32;\n  --secondary: #030302;\n  --light-bg: #fef9f4;\n  --text-dark: #2d2d2d;\n  --tab-radius: 12px;\n  --shadow: 0 4px 12px rgba(0, 0, 0, 0.08);\n  --code-bg: #001f3f;\n  --code-text: #d4f1ff;\n}\n\n.wp_blog_container {\n  font-family: 'Segoe UI', sans-serif;\n  background: var(--light-bg);\n  margin: 0;\n  padding: 0;\n  color: var(--text-dark);\n}\n\n\/* Heading *\/\n.wp_blog_main-heading {\n  text-align: center;\n  font-size: 2.4rem;\n  color: var(--primary);\n  margin-top: 2.5rem;\n  font-weight: bold;\n}\n\n\/* Explanation Card *\/\n.wp_blog_explanation,\n.wp_blog_code-tabs-container {\n  max-width: 940px;\n  margin: 2rem auto;\n  padding: 2rem;\n  background: white;\n  border-radius: var(--tab-radius);\n  box-shadow: var(--shadow);\n}\n\n\/* Text and Visuals *\/\n.wp_blog_explanation h2 {\n  font-size: 1.4rem;\n  color: var(--primary);\n  margin-bottom: 0.5rem;\n}\n\n.wp_blog_explanation p,\n.wp_blog_explanation li {\n  font-size: 1.05rem;\n  line-height: 1.7;\n  margin: 0.5rem 0;\n}\n\n.wp_blog_explanation code {\n  background: #fef9f4; 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\/* makes it the reference for absolute children *\/\n}\n\n.wp_blog_toggle-btn {\n  position: absolute;\n  top: 1rem;\n  right: 1rem;\n  z-index: 9999;\n  padding: 0.5rem 0.8rem;\n  border-radius: 10%;\n  background: var(--primary);\n  color: white;\n  font-weight: bold;\n  cursor: pointer;\n  border: none;\n  box-shadow: var(--shadow);\n  transition: background 0.3s, transform 0.2s;\n}\n\n.wp_blog_toggle-btn:hover {\n  background: #cc772e;\n}\n\n.wp_blog_theme.dark-mode .wp_blog_code-tabs-container {\n  background: #1e1e1e;\n}\n<\/style>\n\n<div class=\"wp_blog_container wp_blog_theme\">\n      <button id=\"blogNotesThemeToggle\" class=\"wp_blog_toggle-btn\">\ud83c\udf19<\/button>\n\n    <h1 class=\"wp_blog_main-heading\"><\/h1>\n\n    <div class=\"wp_blog_explanation\">\n        <h2>Priority Queues<\/h2>\n        <p>A <code>queue<\/code> which serves elements based on <strong>priority<\/strong>, irrespective of their <code>insertion order<\/code>.<\/code><\/p>\n        <h3>Real Life Example<\/h3>\n        <ul>\n            <li>In Hospital \ud83c\udfe5 <\/li>\n            <li>Patient A: Fever<\/li>\n            <li>Patient B: Accident<\/li>\n            <li>Patient C: Headache<\/li>\n        <\/ul>\n        <p>Here, <code>Tasks with higher priority<\/code> should be treated first.<\/p>\n        <ul>\n            <li><code>Normal Queue (FIFO)<\/code> <strong> A -> B -> C<\/strong><\/li>\n            <li><code>Priority Queue (Highest Priority)<\/code> <strong> B -> C -> A<\/strong><\/li>\n            <li>Higher the <code>Priority<\/code> faster will be treated.<\/li>\n        <\/ul>\n\n        <h2>Use Cases:<\/h2>\n        <ul>\n            <li>CPU Scheduling<\/li>\n            <li>Cache System<\/li>\n            <li>Real Time Systems<\/li>\n            <li>Dijkstra&#8217;s Algorithm<\/li>\n        <\/ul>\n        <h2>Implementation of Priority Queue<\/h2>\n       <h3>1. Sorting<\/h3>\n        <img decoding=\"async\" src=\"https:\/\/namastedev.com\/blog\/wp-content\/uploads\/2025\/08\/Screenshot-2025-08-12-at-1.32.56\u202fPM.png\" alt=\"\">\n\n        <h2>Implementation<\/h2>\n        <ul>\n            <li>Whenever you <strong>add elements<\/strong>, ensure that the <code>highest priority<\/code> element is at the front.<\/li>\n            <li>When you <code>add elements<\/code>, make sure you sort them in <code>descending order<\/code>.<\/li>\n        <\/ul>\n        <pre>\n            <code>\n            priorityQueue.push(val);\n            priorityQueue.sort();   \/\/ In descending order\n            <\/code>\n        <\/pre>\n        <h2>Time Complexity<\/h2>\n        <ul>\n           <li>\n            <p>To add an element <code>O(nlogn)<\/code><\/p>\n            <p>Sorting is one way to implement a priority queue, but it has very high time complexity.<\/p>\n            <p>So, Sorting is not efficent way to handling Priority Queue.<\/p>\n            <\/li> \n        <\/ul>\n\n        <h2>2. Heap<\/h2>\n        <h4>Note<\/h4>\n        <ul>\n            <li><code>Heap and Priority Queue<\/code> is not the <strong>same thing<\/strong>.<\/li>\n            <li><code>Heap is Data structure<\/code>.<\/li>\n            <li><code>Priority Queue is abstract data type<\/code>.<\/li>\n            <li>We use <code>Heap<\/code> to implement <code>Priority Queue.<\/code><\/li>\n        <\/ul>\n        <p>A <code>Max Heap<\/code> always ensures that the maximum value is at the top.<\/p>\n        <p><strong>Time Complexity: <\/strong><code>O(logn)<\/code><\/p>\n        <p>This process is efficient for <strong>insertions and deletions<\/strong>.<\/p>\n   \n        <h2>Priority Queue&#8217;s are Two Types:<\/h2>\n        <ul>\n            <li><strong>Max Priority Queue<\/strong>: Where the element with the <code>highest value<\/code> has the <code>highest priority<\/code> and is served before all other elements.<\/li>\n            <li><strong>Min Priority Queue<\/strong>: Where the element with the <code>lowest value<\/code> has the <code>highest priority<\/code> and is served before all other elements.<\/li>\n        <\/ul>\n        <p><strong>Both are very similar to maxHeap and minHeap.<\/strong><\/p>\n    \n    <h2>Implementation of Priority Queue<\/h2>\n    <h2>Java:<\/h2>\n    <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n    <pre>\n      import java.util.PriorityQueue;\n      import java.util.Collections;   \/\/ For reverseOrder()\n        \n      public class PriorityQueueExample {\n        \n      public static void main(String[] args){\n        \/\/ Default min-heap (natural ordering)\n        \n        PriorityQueue<Integer> minHeap = new PriorityQueue<>();\n        \n        minHeap.add(5);\n        \n        minHeap.add(1);\n        \n        minHeap.add(8);\n        \n        System.out.println(\"Min-Heap Head: \" + minHeap.peek());\n        System.out.println(\"Removed from Min-Heap: \" + minHeap.poll());  \n        \n        \/\/ Max-heap using a custom Comparator\n        PriorityQueue<Integer> maxHeap = new PriorityQueue<>(Collections.reverseOrder());\n        \n        maxHeap.add(5);\n        \n        maxHeap.add(1);\n        \n        maxHeap.add(8);\n        \n        System.out.println(\"Max-Heap Head: \" + maxHeap.peek());\n        System.out.println(\"Removed from Max-Heap: \" + maxHeap.poll());\n    }\n}\n<\/pre>\n    <\/div>\n        <p><strong>Java has an in-built PriorityQueue.<\/strong><\/p>\n\n        <h2>Python:<\/h2>\n        <h4>Python provides two main ways to implement priority queues:<\/h4>      \n        <p>\n            <code>heapq module<\/code>: This module provides an implementation of the heap queue algorithm, which is a min-heap. This means the smallest element (highest priority in a typical priority queue implementation, where lower values indicate higher priority) is always at the root of the heap.\n        <\/p>\n    <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n        <pre>\n            import heapq\n            #Create an empty heap (List)\n            priority_queue=[]\n\n            #Add elements as (priority, value) tuples\n            heapq.heappush(priority_queue, (2, \"Task B\"))\n            heapq.heappush(priority_queue, (1, \"Task A\"))\n            heapq.heappush(priority_queue, (3, \"Task C\"))\n\n            #Retrieve and remove elements (Lowest priority value first)\n            while priority_queue:\n                priority, value = heapq.heappop(priority_queue)\n                print(f\"Processing task: {value} (Priority: {priority})\")\n        <\/pre>\n    <\/div>\n\n        <p><code>queue.PriorityQueue<\/code> class: This class from the <code>queue<\/code> module provides a thread-safe implementation of a priority queue, suitable for concurrent applications.<\/p>\n        <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n        <pre>\n            from queue import PriorityQueue\n\n            # Create a PriorityQueue object\n            priority_queue = PriorityQueue()\n\n            # Add elements as (priority, value) tuples\n            priority_queue.put((2, \"Task B\"))\n            priority_queue.put((1, \"Task A\"))\n            priority_queue.put((3, \"Task C\"))\n\n            # Retrieve and remove elements (lowest priority value first)\n            while not priority_queue.empty():\n                priority, value = priority_queue.get()\n                print(f\"Processing task: {value} (Priority: {priority})\")\n        <\/pre>\n        <\/div>\n\n        <h2>C++:<\/h2>\n        <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n        <pre>\n            #include &lt;iostream&gt;\n            #include &lt;queue&gt; \/\/ Required for priority_queue\n\n            int main() {\n                std::priority_queue<int> pq; \/\/ Creates a max-heap (default)\n\n                pq.push(10);\n                pq.push(30);\n                pq.push(28);\n\n                std::cout << \"Top element: \" << pq.top() << std::endl; \/\/ Output: 30\n\n                pq.pop(); \/\/ Removes 30\n\n                std::cout << \"New top element: \" << pq.top() << std::endl; \/\/ Output: 28\n\n                return 0;\n            }\n        <\/pre>\n    <\/div>\n        <h2>JavaScript:<\/h2>\n        <p>In Javascript <strong> does not<\/strong> have a <code>built<\/code> in <code>Priority Queue \/ Heap<\/code>.<\/p>\n        <p>You have to write your own <code>implementation<\/code>.<\/p>\n    <\/div>\n<\/div>\n\n<script>\ndocument.addEventListener(\"DOMContentLoaded\", () => {\n  const buttons = document.querySelectorAll(\".wp_blog_code-tab-button\");\n  const contents = document.querySelectorAll(\".wp_blog_code-tab-content\");\n\n  buttons.forEach((button) => {\n    button.addEventListener(\"click\", () => {\n      const lang = button.getAttribute(\"data-lang\");\n\n      buttons.forEach((btn) => btn.classList.remove(\"active\"));\n      contents.forEach((content) => content.classList.remove(\"active\"));\n\n      button.classList.add(\"active\");\n      document\n        .querySelector(`.wp_blog_code-tab-content[data-lang=\"${lang}\"]`)\n        .classList.add(\"active\");\n    });\n  });\n\n  const themeToggle = document.getElementById(\"blogNotesThemeToggle\");\n  const themeContainer = document.querySelector(\".wp_blog_theme\");\n\n  themeToggle.addEventListener(\"click\", () => {\n    themeContainer.classList.toggle(\"dark-mode\");\n    themeToggle.textContent =\n      themeContainer.classList.contains(\"dark-mode\") ? \"\u2600\ufe0f\" : \"\ud83c\udf19\";\n  });\n});\n<\/script>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\ud83c\udf19 Priority Queues A queue which serves elements based on priority, irrespective of their insertion order. Real Life Example In Hospital \ud83c\udfe5 Patient A: Fever Patient B: Accident Patient C: Headache Here, Tasks with higher priority should be treated first. Normal Queue (FIFO) A -> B -> C Priority Queue (Highest Priority) B -> C<\/p>\n","protected":false},"author":108,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[210,322,260,176,175,211,811,810,174,172,173],"tags":[],"class_list":{"0":"post-9239","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-algorithms","7":"category-algorithms-and-data-structures","8":"category-c-c-plus-plus","9":"category-csharp","10":"category-cplusplus","11":"category-data-structures","12":"category-data-structures-and-algorithms","13":"category-dsa","14":"category-java","15":"category-javascript","16":"category-python"},"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/9239","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/users\/108"}],"replies":[{"embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/comments?post=9239"}],"version-history":[{"count":2,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/9239\/revisions"}],"predecessor-version":[{"id":10348,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/9239\/revisions\/10348"}],"wp:attachment":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/media?parent=9239"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/categories?post=9239"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/tags?post=9239"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}