Refactor MinHeap.

src/data-structures/priority-queue/PriorityQueue.js

@@ -0,0 +1,23 @@
+import MinHeap from '../heap/MinHeap';
+
+// 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 = {};
+  }
+
+  add(item, priority = 0) {
+    this.priorities[item] = priority;
+    super.add(item);
+  }
+
+  compare(a, b) {
+    if (this.priorities[a] === this.priorities[b]) {
+      return 0;
+    }
+
+    return this.priorities[a] < this.priorities[b] ? -1 : 1;
+  }
+}

src/data-structures/priority-queue/__test__/PriorityQueue.test.js

@@ -0,0 +1,34 @@
+import PriorityQueue from '../PriorityQueue';
+
+describe('PriorityQueue', () => {
+  it('should create default priority queue', () => {
+    const priorityQueue = new PriorityQueue();
+
+    expect(priorityQueue).toBeDefined();
+  });
+
+  it('should insert items to the queue and respect priorities', () => {
+    const priorityQueue = new PriorityQueue();
+
+    priorityQueue.add(10, 1);
+    expect(priorityQueue.peek()).toBe(10);
+
+    priorityQueue.add(5, 2);
+    expect(priorityQueue.peek()).toBe(10);
+
+    priorityQueue.add(100, 0);
+    expect(priorityQueue.peek()).toBe(100);
+  });
+
+  it('should poll from queue with respect to priorities', () => {
+    const priorityQueue = new PriorityQueue();
+
+    priorityQueue.add(10, 1);
+    priorityQueue.add(5, 2);
+    priorityQueue.add(100, 0);
+
+    expect(priorityQueue.poll()).toBe(100);
+    expect(priorityQueue.poll()).toBe(10);
+    expect(priorityQueue.poll()).toBe(5);
+  });
+});