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chapter 11: heap
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‎src/11-heap/01-min-heap.js‎

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// src/11-heap/01-min-heap.js
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const Heap = require('./heap');
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class Task {
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constructor(id, priority, executionTime) {
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this.id = id;
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this.priority = priority;
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this.executionTime = executionTime;
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}
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}
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class TaskScheduler {
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constructor() {
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this.taskQueue = new Heap((a,b) => a.priority - b.priority);
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}
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addTask(task) {
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this.taskQueue.insert(task);
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}
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scheduleNextTask() {
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if (this.taskQueue.isEmpty()) {
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return null; // No tasks to schedule
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}
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return this.taskQueue.extract();
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}
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}
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const scheduler = new TaskScheduler();
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scheduler.addTask(new Task(2, 2, 10));
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scheduler.addTask(new Task(3, 3, 5));
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scheduler.addTask(new Task(4, 4, 8));
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scheduler.addTask(new Task(5, 5, 15));
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scheduler.addTask(new Task(1, 1, 20));
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console.log(scheduler.taskQueue.toArray());
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console.log(scheduler.scheduleNextTask()); // Output: Task 1 (highest priority)
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console.log(scheduler.taskQueue.toArray());
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// to see the output of this file use the command: node src/11-heap/01-min-heap.js

‎src/11-heap/02-max-heap.js‎

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// src/11-heap/02-max-heap.js
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const Heap = require('./heap');
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class Patient {
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constructor(name, priority) {
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this.name = name;
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this.priority = priority;
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}
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}
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const PRIORITY = { LOW: 1, MEDIUM: 2, HIGH: 3 };
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const erHeap = new Heap((a, b) => b.priority - a.priority);
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erHeap.insert(new Patient('Poppy', PRIORITY.LOW));
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erHeap.insert(new Patient('Kieran', PRIORITY.HIGH));
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erHeap.insert(new Patient('Camila', PRIORITY.MEDIUM));
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erHeap.insert(new Patient('Casteel', PRIORITY.LOW));
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erHeap.insert(new Patient('Mike', PRIORITY.HIGH));
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console.log('Head', erHeap.toArray());
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while (!erHeap.isEmpty()) {
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const patient = erHeap.extract();
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console.log('Next patient:', patient.name, patient.priority);
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}
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// Next patient: Kieran 3
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// Next patient: Mike 3
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// Next patient: Camila 2
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// Next patient: Casteel 1
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// Next patient: Poppy 1
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// to see the output of this file use the command: node src/11-heap/02-max-heap.js

‎src/11-heap/03-heap-sort.js‎

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// src/11-heap/03-heap-sort.js
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const Comparator = require('../10-tree/comparator');
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const Heap = require('./heap');
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const HeapSort = require('./heap-sort');
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const heapSort = (array, compareFn = Comparator.defaultCompareFn) => {
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const heap = new Heap(compareFn);
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heap.heapify(array);
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const sortedArray = [];
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while (!heap.isEmpty()){
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sortedArray.push(heap.extract());
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}
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return heap.toArray();
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};
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// using the Heap class and the heapify method
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let unsortedArray = [7, 6, 3, 5, 4, 1, 2];
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console.log(heapSort(unsortedArray)); // [1, 2, 3, 4, 5, 6, 7]
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// using the heap sort algorithm
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const unsortedArray = [7, 6, 3, 5, 4, 1, 2];
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HeapSort(unsortedArray); // will modify the array in place
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console.log(unsortedArray); // [1, 2, 3, 4, 5, 6, 7]
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// to see the output of this file use the command: node src/11-heap/03-heap-sort.js

‎src/11-heap/heap-sort.js‎

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// src/11-heap/heap-sort.js
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const Comparator = require('../10-tree/comparator');
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/**
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* Heapify the array.
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* @param {*} array to be heapified.
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* @param {*} heapSize size of the heap.
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* @param {*} rootIndex index of the root.
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* @param {*} compareFn compare function.
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*/
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const siftDown = (array, heapSize, rootIndex, compareFn) => {
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let largest = rootIndex;
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let left = 2 * rootIndex + 1;
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let right = 2 * rootIndex + 2;
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if (left < heapSize && compareFn.greaterThan(array[left], array[largest])) {
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largest = left;
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}
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if (right < heapSize && compareFn.greaterThan(array[right], array[largest])) {
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largest = right;
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}
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if (largest !== rootIndex) {
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[array[rootIndex], array[largest]] = [array[largest], array[rootIndex]];
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siftDown(array, heapSize, largest, compareFn);
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}
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};
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/**
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* Build max heap.
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* @param {*} array to be heapified.
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* @param {*} compareFn compare function.
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*/
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const buildMaxHeap = (array, compareFn) => {
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const heapSize = array.length;
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for (let i = Math.floor(heapSize / 2) - 1; i >= 0; i--) {
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siftDown(array, heapSize, i, compareFn);
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}
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}
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/**
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* Heap sort algorithm.
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* @param {*} array to be sorted.
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* @param {*} compareFn compare function.
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*/
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const HeapSort = (array, compareFn = Comparator.defaultCompareFn) => {
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const defaultCompareFn = new Comparator(compareFn);
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buildMaxHeap(array, defaultCompareFn);
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for (let i = array.length - 1; i > 0; i--) {
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[array[0], array[i]] = [array[i], array[0]];
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siftDown(array, i, 0, defaultCompareFn);
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}
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}
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module.exports = HeapSort;

‎src/11-heap/heap.js‎

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// src/11-heap/heap.js
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const Comparator = require('../10-tree/comparator');
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class Heap {
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#heap = [];
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#compareFn;
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constructor(compareFn = Comparator.defaultCompareFn) {
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this.#compareFn = new Comparator(compareFn);
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}
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getLeftChildIndex(parentIndex) {
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return 2 * parentIndex + 1;
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}
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getRightChildIndex(parentIndex) {
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return 2 * parentIndex + 2;
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}
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getParentIndex(childIndex) {
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if (childIndex === 0) { return undefined; }
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return Math.floor((childIndex - 1) / 2);
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}
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insert(value) {
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if (value) {
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const index = this.#heap.length;
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this.#heap.push(value);
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this.#siftUp(index);
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return true;
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}
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return false;
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}
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#siftUp(index) {
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const parentIndex = this.getParentIndex(index);
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if (parentIndex !== undefined && parentIndex >= 0 &&
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this.#compareFn.greaterThan(this.#heap[parentIndex], this.#heap[index])
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) {
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[this.#heap[parentIndex], this.#heap[index]] = [this.#heap[index], this.#heap[parentIndex]];
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this.#siftUp(parentIndex);
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}
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}
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extract() {
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if (this.#heap.length === 0) {
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return undefined;
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}
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if (this.#heap.length === 1) {
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return this.#heap.shift();
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}
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const root = this.#heap[0];
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this.#heap[0] = this.#heap.pop();
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this.#siftDown(0);
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return root;
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}
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#siftDown(index) {
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const leftIndex = this.getLeftChildIndex(index);
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const rightIndex = this.getRightChildIndex(index);
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let smallerIndex = index;
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if (leftIndex < this.#heap.length &&
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this.#compareFn.lessThan(this.#heap[leftIndex], this.#heap[smallerIndex])
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) {
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smallerIndex = leftIndex;
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}
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if (rightIndex < this.#heap.length &&
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this.#compareFn.lessThan(this.#heap[rightIndex], this.#heap[smallerIndex])
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) {
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smallerIndex = rightIndex;
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}
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if (smallerIndex !== index) {
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[this.#heap[index], this.#heap[smallerIndex]] = [this.#heap[smallerIndex], this.#heap[index]];
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this.#siftDown(smallerIndex);
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}
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}
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heapify(array) {
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this.#heap = array;
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const lastParentIndex = this.getParentIndex(this.#heap.length - 1);
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if (lastParentIndex !== undefined) {
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for (let i = lastParentIndex; i >= 0; i--) {
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this.#siftDown(i);
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}
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}
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}
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peek() {
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return this.#heap.length === 0 ? undefined : this.#heap[0];
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}
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get size() {
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return this.#heap.length;
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}
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isEmpty() {
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return this.#heap.length === 0;
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}
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toArray() {
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return this.#heap.slice();
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}
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clear() {
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this.#heap = [];
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}
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toString() {
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return this.#heap.toString();
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}
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}
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module.exports = Heap;

‎src/11-heap/leetcode/minimum-number-game.ts‎

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// https://leetcode.com/problems/minimum-number-game/description/
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// 2974. Minimum Number Game
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function siftDown (array: number[], heapSize: number, rootIndex: number) {
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let largest = rootIndex;
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let left = 2 * rootIndex + 1;
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let right = 2 * rootIndex + 2;
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if (left < heapSize && array[left] > array[largest]) {
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largest = left;
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}
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if (right < heapSize && array[right] > array[largest]) {
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largest = right;
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}
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if (largest !== rootIndex) {
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[array[rootIndex], array[largest]] = [array[largest], array[rootIndex]];
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siftDown(array, heapSize, largest);
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}
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};
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function buildMaxHeap (array: number[]) {
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const heapSize = array.length;
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for (let i = Math.floor(heapSize / 2) - 1; i >= 0; i--) {
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siftDown(array, heapSize, i);
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}
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}
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function heapSort(array: number[]) {
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buildMaxHeap(array);
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for (let i = array.length - 1; i > 0; i--) {
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[array[0], array[i]] = [array[i], array[0]];
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siftDown(array, i, 0);
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}
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}
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function numberGame(nums: number[]): number[] {
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// nums.sort((a, b) => a - b);
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heapSort(nums);
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const arr: number[] = [];
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while (nums.length > 0) {
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const alice = nums.splice(0, 1)[0];
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const bob = nums.splice(0, 1)[0];
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arr.push(bob);
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arr.push(alice);
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}
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return arr;
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};
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console.log(numberGame([5,4,2,3])); // [ 3, 2, 5, 4 ]
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console.log(numberGame([2,5])); // [ 5, 2 ]
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// Time complexity: O(nlogn)
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// Space complexity: O(n)
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// to see the output of this file use the command: npx ts-node src/11-heap/leetcode/minimum-number-game.ts

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