PriorityQueue.js

import MinHeap from '../heap/MinHeap';
import Comparator from '../../utils/comparator/Comparator';

// It is the same as min heap except that when comparing to elements
// we take into account not element's value but rather its priority.
export default class PriorityQueue extends MinHeap {
 constructor() {
 super();
 this.priorities = {};
 this.compare = new Comparator(this.comparePriority.bind(this));
 }

 /**
 * @param {*} item
 * @param {number} [priority]
 * @return {PriorityQueue}
 */
 add(item, priority = 0) {
 this.priorities[item] = priority;
 super.add(item);

 return this;
 }

 /**
 * @param {*} item
 * @param {Comparator} [customFindingComparator]
 * @return {PriorityQueue}
 */
 remove(item, customFindingComparator) {
 super.remove(item, customFindingComparator);
 delete this.priorities[item];

 return this;
 }

 /**
 * @param {*} item
 * @param {number} priority
 * @return {PriorityQueue}
 */
 changePriority(item, priority) {
 this.remove(item, new Comparator(this.compareValue));
 this.add(item, priority);

 return this;
 }

 /**
 * @param {*} item
 * @return {Number[]}
 */
 findByValue(item) {
 return this.find(item, new Comparator(this.compareValue));
 }

 /**
 * @param {*} item
 * @return {boolean}
 */
 hasValue(item) {
 return this.findByValue(item).length > 0;
 }

 /**
 * @param {*} a
 * @param {*} b
 * @return {number}
 */
 comparePriority(a, b) {
 if (this.priorities[a] === this.priorities[b]) {
 return 0;
 }

 return this.priorities[a] < this.priorities[b] ? -1 : 1;
 }

 /**
 * @param {*} a
 * @param {*} b
 * @return {number}
 */
 compareValue(a, b) {
 if (a === b) {
 return 0;
 }

 return a < b ? -1 : 1;
 }
}