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Make it possible to use objects in priority queue.
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@ -1,52 +1,59 @@
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import MinHeap from '../heap/MinHeap';
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import Comparator from '../../utils/comparator/Comparator';
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// It is the same as min heap except that when comparing to elements
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// we take into account not element's value but rather its priority.
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// It is the same as min heap except that when comparing two elements
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// we take into account its priority instead of the element's value.
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export default class PriorityQueue extends MinHeap {
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constructor() {
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// Call MinHip constructor first.
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super();
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this.priorities = {};
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// Setup priorities map.
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this.priorities = new Map();
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// Use custom comparator for heap elements that will take element priority
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// instead of element value into account.
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this.compare = new Comparator(this.comparePriority.bind(this));
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}
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/**
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* @param {*} item
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* @param {number} [priority]
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* Add item to the priority queue.
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* @param {*} item - item we're going to add to the queue.
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* @param {number} [priority] - items priority.
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* @return {PriorityQueue}
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*/
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add(item, priority = 0) {
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this.priorities[item] = priority;
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this.priorities.set(item, priority);
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super.add(item);
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return this;
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}
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/**
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* @param {*} item
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* @param {Comparator} [customFindingComparator]
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* Remove item from priority queue.
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* @param {*} item - item we're going to remove.
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* @param {Comparator} [customFindingComparator] - custom function for finding the item to remove
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* @return {PriorityQueue}
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*/
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remove(item, customFindingComparator) {
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super.remove(item, customFindingComparator);
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delete this.priorities[item];
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this.priorities.delete(item);
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return this;
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}
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/**
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* @param {*} item
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* @param {number} priority
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* Change priority of the item in a queue.
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* @param {*} item - item we're going to re-prioritize.
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* @param {number} priority - new item's priority.
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* @return {PriorityQueue}
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*/
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changePriority(item, priority) {
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this.remove(item, new Comparator(this.compareValue));
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this.add(item, priority);
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return this;
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}
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/**
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* Find item by ite value.
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* @param {*} item
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* @return {Number[]}
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*/
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@ -55,6 +62,7 @@ export default class PriorityQueue extends MinHeap {
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}
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/**
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* Check if item already exists in a queue.
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* @param {*} item
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* @return {boolean}
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*/
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@ -63,19 +71,20 @@ export default class PriorityQueue extends MinHeap {
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}
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/**
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* Compares priorities of two items.
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* @param {*} a
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* @param {*} b
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* @return {number}
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*/
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comparePriority(a, b) {
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if (this.priorities[a] === this.priorities[b]) {
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if (this.priorities.get(a) === this.priorities.get(b)) {
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return 0;
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}
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return this.priorities[a] < this.priorities[b] ? -1 : 1;
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return this.priorities.get(a) < this.priorities.get(b) ? -1 : 1;
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}
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/**
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* Compares values of two items.
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* @param {*} a
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* @param {*} b
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* @return {number}
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@ -84,7 +93,6 @@ export default class PriorityQueue extends MinHeap {
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if (a === b) {
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return 0;
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}
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return a < b ? -1 : 1;
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}
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}
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@ -20,6 +20,23 @@ describe('PriorityQueue', () => {
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expect(priorityQueue.peek()).toBe(100);
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});
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it('should be possible to use objects in priority queue', () => {
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const priorityQueue = new PriorityQueue();
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const user1 = { name: 'Mike' };
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const user2 = { name: 'Bill' };
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const user3 = { name: 'Jane' };
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priorityQueue.add(user1, 1);
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expect(priorityQueue.peek()).toBe(user1);
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priorityQueue.add(user2, 2);
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expect(priorityQueue.peek()).toBe(user1);
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priorityQueue.add(user3, 0);
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expect(priorityQueue.peek()).toBe(user3);
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});
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it('should poll from queue with respect to priorities', () => {
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const priorityQueue = new PriorityQueue();
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