Priority Queue Data Structure in JavaScript 🚀

0-5 minutes: Check the Home Task

• Review solutions.
• Discuss any issues and common mistakes encountered.
• Clarify doubts related to the home task.

Key Points to Address:

• If any of the students faced issues with basic concepts like arrays, linked lists, or queues, address those foundational concepts briefly before moving forward.
• Explain the Priority Queue data structure to everyone:
  • A Priority Queue is a special type of queue where each element is associated with a priority.
  • Elements with higher priority are dequeued before elements with lower priority, regardless of their insertion order.
  • The key operations are:
    • enqueue(element, priority): Adds an element to the queue with a given priority.
    • dequeue(): Removes and returns the element with the highest priority.
    • peek(): Returns the element with the highest priority without removing it.
    • isEmpty(): Checks if the queue is empty.

5-10 minutes: Introduction to Priority Queue and its Key Operations

• Explain the Priority Queue data structure and its real-world analogy (like a hospital emergency room).
• Discuss key operations:
  • enqueue(element, priority): Adds an element to the queue with a given priority.
  • dequeue(): Removes and returns the element with the highest priority.
  • peek(): Returns the element with the highest priority without removing it.
  • isEmpty(): Checks if the queue is empty.

10-20 minutes: Implement a Priority Queue Class from Scratch

• Guide students to implement a Priority Queue class in JavaScript.
• The class should support the following methods:
  • enqueue(element, priority)
  • dequeue()
  • peek()
  • isEmpty()

Example:

class PriorityQueue {
  constructor() {
    this.items = [];
  }

  // Adds an element with a priority
  enqueue(element, priority) {
    const queueElement = { element, priority };
    let added = false;

    for (let i = 0; i < this.items.length; i++) {
      if (queueElement.priority < this.items[i].priority) {
        this.items.splice(i, 0, queueElement);
        added = true;
        break;
      }
    }

    if (!added) {
      this.items.push(queueElement);
    }
  }

  // Removes and returns the element with the highest priority
  dequeue() {
    if (this.isEmpty()) {
      return 'Priority Queue is empty';
    }
    return this.items.shift();
  }

  // Returns the element with the highest priority without removing it
  peek() {
    if (this.isEmpty()) {
      return 'Priority Queue is empty';
    }
    return this.items[0];
  }

  // Checks if the queue is empty
  isEmpty() {
    return this.items.length === 0;
  }
}

// Example usage:
const pq = new PriorityQueue();
pq.enqueue('Patient A', 2);
pq.enqueue('Patient B', 1);
pq.enqueue('Patient C', 3);

console.log(pq.dequeue()); // { element: 'Patient B', priority: 1 }
console.log(pq.peek());    // { element: 'Patient A', priority: 2 }
console.log(pq.isEmpty()); // false

20-30 minutes: Task - Solve a Problem Using a Priority Queue

• Assign a task where students need to solve a problem using the Priority Queue.
• Example problem: Simulate a system that handles customer service requests with different priority levels.

Example:

function customerSupportSystem(requests) {
  const pq = new PriorityQueue();

  requests.forEach(request => {
    pq.enqueue(request.name, request.priority);
  });

  while (!pq.isEmpty()) {
    const served = pq.dequeue();
    console.log(`Serving: ${served.element} with priority ${served.priority}`);
  }
}

const requests = [
  { name: 'Request A', priority: 3 },
  { name: 'Request B', priority: 1 },
  { name: 'Request C', priority: 2 }
];

customerSupportSystem(requests);

30-40 minutes: Home Task - Solve a Problem Using Priority Queue from LeetCode

• Provide a LeetCode problem that can be solved using the Priority Queue data structure.
• Students can work on this problem during the session or as homework.

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