Add heap sort.

src/data-structures/heap/MinHeap.js

@@ -1,10 +1,10 @@
 import Comparator from '../../utils/comparator/Comparator';
 
 export default class MinHeap {
-  constructor() {
+  constructor(comparatorFunction) {
     // Array representation of the heap.
     this.heapContainer = [];
-    this.compare = new Comparator();
+    this.compare = new Comparator(comparatorFunction);
   }
 
   static getLeftChildIndex(parentIndex) {
@@ -120,6 +120,10 @@ export default class MinHeap {
     }
   }
 
+  isEmpty() {
+    return !this.heapContainer.length;
+  }
+
   toString() {
     return this.heapContainer.toString();
   }

src/data-structures/heap/__test__/MinHeap.test.js

@@ -6,12 +6,14 @@ describe('MinHeap', () => {
 
     expect(minHeap).toBeDefined();
     expect(minHeap.peek()).toBeNull();
+    expect(minHeap.isEmpty()).toBeTruthy();
   });
 
   it('should add items to the heap and heapify it up', () => {
     const minHeap = new MinHeap();
 
     minHeap.add(5);
+    expect(minHeap.isEmpty()).toBeFalsy();
     expect(minHeap.peek()).toBe(5);
     expect(minHeap.toString()).toBe('5');