class Node {
  constructor(val) {
    this.val = val;
    this.next = null;
  }
}

class LinkedList {
  constructor() {
    this.head = null;
  }

  reverse() {
    let prev = null;
    let current = this.head;
    while (current !== null) {
      let next = current.next;
      current.next = prev;
      prev = current;
      current = next;
    }
    this.head = prev;
  }

  append(val) {
    let newNode = new Node(val);
    if (!this.head) {
      this.head = newNode;
      return;
    }
    let current = this.head;
    while (current.next) {
      current = current.next;
    }
    current.next = newNode;
  }

  printList() {
    let current = this.head;
    let output = '';
    while (current) {
      output += current.val + ' ';
      current = current.next;
    }
    console.log(output);
  }
}

// Example usage
let ll = new LinkedList();
ll.append(1);
ll.append(2);
ll.append(3);
console.log("Original List:");
ll.printList();
ll.reverse();
console.log("Reversed List:");
ll.printList();

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

  // Add element with priority
  enqueue(val, priority) {
    this.heap.push({ val, priority });
    this.heapifyUp();
  }

  // Remove and return element with highest priority (lowest number)
  dequeue() {
    if (this.heap.length === 0) return null;
    if (this.heap.length === 1) return this.heap.pop();
    let min = this.heap[0];
    this.heap[0] = this.heap.pop();
    this.heapifyDown();
    return min;
  }

  heapifyUp() {
    let idx = this.heap.length - 1;
    let parentIdx = Math.floor((idx - 1) / 2);
    while (idx > 0 && this.heap[idx].priority < this.heap[parentIdx].priority) {
      [this.heap[idx], this.heap[parentIdx]] = [this.heap[parentIdx], this.heap[idx]];
      idx = parentIdx;
      parentIdx = Math.floor((idx - 1) / 2);
    }
  }

  heapifyDown() {
    let idx = 0;
    let leftChild = 2 * idx + 1;
    while (leftChild < this.heap.length) {
      let minChild = leftChild;
      let rightChild = leftChild + 1;
      if (rightChild < this.heap.length && this.heap[rightChild].priority < this.heap[leftChild].priority) {
        minChild = rightChild;
      }
      if (this.heap[idx].priority <= this.heap[minChild].priority) break;
      [this.heap[idx], this.heap[minChild]] = [this.heap[minChild], this.heap[idx]];
      idx = minChild;
      leftChild = 2 * idx + 1;
    }
  }
}

// Example usage
let pq = new PriorityQueue();
pq.enqueue('low', 1);
pq.enqueue('high', 0);
pq.enqueue('medium', 2);
console.log(pq.dequeue()); // { val: 'high', priority: 0 }
console.log(pq.dequeue()); // { val: 'low', priority: 1 }
console.log(pq.dequeue()); // { val: 'medium', priority: 2 }

Meta AI Response: Reversing a Linked List in JavaScript To reverse a singly linked list in JavaScript, you can use the following implementation: class Node { constructor(val) { this.val = val; this.next = null; } } class LinkedList { constructor() { this.head = null; } reverse() { let prev = null; let current = this.head; while (current !== null) { let next = current.next; current.next = prev; prev = current; current = next; } this.head = prev; } append(val) { let newNode = new Node(val); if (!this.head) { this.head = newNode; return; } let current = this.head; while (current.next) { current = current.next; } current.next = newNode; } printList() { let current = this.head; let output = ''; while (current) { output += current.val + ' '; current = current.next; } console.log(output); } } // Example usage let ll = new LinkedList(); ll.append(1); ll.append(2); ll.append(3); console.log("Original List:"); ll.printList(); ll.reverse(); console.log("Reversed List:"); ll.printList(); Priority Queue in JavaScript A priority queue can be implemented using a min-heap or max-heap. Here's a basic implementation of a min-priority queue in JavaScript: class PriorityQueue { constructor() { this.heap = []; } // Add element with priority enqueue(val, priority) { this.heap.push({ val, priority }); this.heapifyUp(); } // Remove and return element with highest priority (lowest number) dequeue() { if (this.heap.length === 0) return null; if (this.heap.length === 1) return this.heap.pop(); let min = this.heap[0]; this.heap[0] = this.heap.pop(); this.heapifyDown(); return min; } heapifyUp() { let idx = this.heap.length - 1; let parentIdx = Math.floor((idx - 1) / 2); while (idx > 0 && this.heap[idx].priority < this.heap[parentIdx].priority) { [this.heap[idx], this.heap[parentIdx]] = [this.heap[parentIdx], this.heap[idx]]; idx = parentIdx; parentIdx = Math.floor((idx - 1) / 2); } } heapifyDown() { let idx = 0; let leftChild = 2 * idx + 1; while (leftChild < this.heap.length) { let minChild = leftChild; let rightChild = leftChild + 1; if (rightChild < this.heap.length && this.heap[rightChild].priority < this.heap[leftChild].priority) { minChild = rightChild; } if (this.heap[idx].priority <= this.heap[minChild].priority) break; [this.heap[idx], this.heap[minChild]] = [this.heap[minChild], this.heap[idx]]; idx = minChild; leftChild = 2 * idx + 1; } } } // Example usage let pq = new PriorityQueue(); pq.enqueue('low', 1); pq.enqueue('high', 0); pq.enqueue('medium', 2); console.log(pq.dequeue()); // { val: 'high', priority: 0 } console.log(pq.dequeue()); // { val: 'low', priority: 1 } console.log(pq.dequeue()); // { val: 'medium', priority: 2 }