Add heap sort.

Author: trekhleb

README.md

@@ -34,6 +34,7 @@
   * [Bubble Sort](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/sorting/bubble-sort)
   * [Selection Sort](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/sorting/selection-sort)
   * [Insertion Sort](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/sorting/insertion-sort)
+  * [Heap Sort](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/sorting/heap-sort)
 
 ## Running Tests
 

src/algorithms/sorting/bubble-sort/__test__/BubbleSort.test.js

@@ -7,6 +7,12 @@ import {
   SortTester,
 } from '../../SortTester';
 
+// Complexity constants.
+const SORTED_ARRAY_VISITING_COUNT = 20;
+const NOT_SORTED_ARRAY_VISITING_COUNT = 280;
+const REVERSE_SORTED_ARRAY_VISITING_COUNT = 400;
+const EQUAL_ARRAY_VISITING_COUNT = 20;
+
 describe('BubbleSort', () => {
   it('should sort array', () => {
     SortTester.testSort(BubbleSort);
@@ -21,42 +27,34 @@ describe('BubbleSort', () => {
   });
 
   it('should visit EQUAL array element specified number of times', () => {
-    const expectedNumberOfVisits = 20;
-
     SortTester.testAlgorithmTimeComplexity(
       BubbleSort,
       equalArr,
-      expectedNumberOfVisits,
+      EQUAL_ARRAY_VISITING_COUNT,
     );
   });
 
   it('should visit SORTED array element specified number of times', () => {
-    const expectedNumberOfVisits = 20;
-
     SortTester.testAlgorithmTimeComplexity(
       BubbleSort,
       sortedArr,
-      expectedNumberOfVisits,
+      SORTED_ARRAY_VISITING_COUNT,
     );
   });
 
   it('should visit NOT SORTED array element specified number of times', () => {
-    const expectedNumberOfVisits = 280;
-
     SortTester.testAlgorithmTimeComplexity(
       BubbleSort,
       notSortedArr,
-      expectedNumberOfVisits,
+      NOT_SORTED_ARRAY_VISITING_COUNT,
     );
   });
 
   it('should visit REVERSE SORTED array element specified number of times', () => {
-    const expectedNumberOfVisits = 400;
-
     SortTester.testAlgorithmTimeComplexity(
       BubbleSort,
       reverseArr,
-      expectedNumberOfVisits,
+      REVERSE_SORTED_ARRAY_VISITING_COUNT,
     );
   });
 });

src/algorithms/sorting/heap-sort/HeapSort.js

@@ -0,0 +1,30 @@
+import Sort from '../Sort';
+import MinHeap from '../../../data-structures/heap/MinHeap';
+
+export default class HeapSort extends Sort {
+  sort(originalArray) {
+    const sortedArray = [];
+    const minHeap = new MinHeap(this.callbacks.compareCallback);
+
+    // Insert all array elements to the heap.
+    originalArray.forEach((element) => {
+      // Call visiting callback.
+      this.callbacks.visitingCallback(element);
+
+      minHeap.add(element);
+    });
+
+    // Now we have min heap with minimal element always on top.
+    // Let's poll that minimal element one by one and thus form the sorted array.
+    while (!minHeap.isEmpty()) {
+      const nextMinElement = minHeap.poll();
+
+      // Call visiting callback.
+      this.callbacks.visitingCallback(nextMinElement);
+
+      sortedArray.push(nextMinElement);
+    }
+
+    return sortedArray;
+  }
+}

src/algorithms/sorting/heap-sort/README.md

@@ -0,0 +1,18 @@
+# Heap Sort
+
+Heapsort is a comparison-based sorting algorithm.
+Heapsort can be thought of as an improved selection
+sort: like that algorithm, it divides its input into
+a sorted and an unsorted region, and it iteratively
+shrinks the unsorted region by extracting the largest
+element and moving that to the sorted region. The 
+improvement consists of the use of a heap data structure
+rather than a linear-time search to find the maximum.
+
+![Algorithm Visualization](https://upload.wikimedia.org/wikipedia/commons/1/1b/Sorting_heapsort_anim.gif)
+
+![Algorithm Visualization](https://upload.wikimedia.org/wikipedia/commons/4/4d/Heapsort-example.gif)
+
+## References
+
+[Wikipedia](https://en.wikipedia.org/wiki/Heapsort)

src/algorithms/sorting/heap-sort/__test__/HeapSort.test.js

@@ -0,0 +1,56 @@
+import HeapSort from '../HeapSort';
+import {
+  equalArr,
+  notSortedArr,
+  reverseArr,
+  sortedArr,
+  SortTester,
+} from '../../SortTester';
+
+// Complexity constants.
+const SORTED_ARRAY_VISITING_COUNT = 40;
+const NOT_SORTED_ARRAY_VISITING_COUNT = 40;
+const REVERSE_SORTED_ARRAY_VISITING_COUNT = 40;
+const EQUAL_ARRAY_VISITING_COUNT = 40;
+
+describe('HeapSort', () => {
+  it('should sort array', () => {
+    SortTester.testSort(HeapSort);
+  });
+
+  it('should sort array with custom comparator', () => {
+    SortTester.testSortWithCustomComparator(HeapSort);
+  });
+
+  it('should visit EQUAL array element specified number of times', () => {
+    SortTester.testAlgorithmTimeComplexity(
+      HeapSort,
+      equalArr,
+      EQUAL_ARRAY_VISITING_COUNT,
+    );
+  });
+
+  it('should visit SORTED array element specified number of times', () => {
+    SortTester.testAlgorithmTimeComplexity(
+      HeapSort,
+      sortedArr,
+      SORTED_ARRAY_VISITING_COUNT,
+    );
+  });
+
+  it('should visit NOT SORTED array element specified number of times', () => {
+    SortTester.testAlgorithmTimeComplexity(
+      HeapSort,
+      notSortedArr,
+      NOT_SORTED_ARRAY_VISITING_COUNT,
+    );
+  });
+
+  it('should visit REVERSE SORTED array element specified number of times', () => {
+    SortTester.testAlgorithmTimeComplexity(
+      HeapSort,
+      reverseArr,
+      REVERSE_SORTED_ARRAY_VISITING_COUNT,
+    );
+  });
+});

src/algorithms/sorting/insertion-sort/__test__/InsertionSort.test.js

@@ -7,6 +7,12 @@ import {
   SortTester,
 } from '../../SortTester';
 
+// Complexity constants.
+const SORTED_ARRAY_VISITING_COUNT = 20;
+const NOT_SORTED_ARRAY_VISITING_COUNT = 101;
+const REVERSE_SORTED_ARRAY_VISITING_COUNT = 210;
+const EQUAL_ARRAY_VISITING_COUNT = 20;
+
 describe('InsertionSort', () => {
   it('should sort array', () => {
     SortTester.testSort(InsertionSort);
@@ -21,42 +27,34 @@ describe('InsertionSort', () => {
   });
 
   it('should visit EQUAL array element specified number of times', () => {
-    const expectedNumberOfVisits = 20;
-
     SortTester.testAlgorithmTimeComplexity(
       InsertionSort,
       equalArr,
-      expectedNumberOfVisits,
+      EQUAL_ARRAY_VISITING_COUNT,
     );
   });
 
   it('should visit SORTED array element specified number of times', () => {
-    const expectedNumberOfVisits = 20;
-
     SortTester.testAlgorithmTimeComplexity(
       InsertionSort,
       sortedArr,
-      expectedNumberOfVisits,
+      SORTED_ARRAY_VISITING_COUNT,
     );
   });
 
   it('should visit NOT SORTED array element specified number of times', () => {
-    const expectedNumberOfVisits = 101;
-
     SortTester.testAlgorithmTimeComplexity(
       InsertionSort,
       notSortedArr,
-      expectedNumberOfVisits,
+      NOT_SORTED_ARRAY_VISITING_COUNT,
     );
   });
 
   it('should visit REVERSE SORTED array element specified number of times', () => {
-    const expectedNumberOfVisits = 210;
-
     SortTester.testAlgorithmTimeComplexity(
       InsertionSort,
       reverseArr,
-      expectedNumberOfVisits,
+      REVERSE_SORTED_ARRAY_VISITING_COUNT,
     );
   });
 });

src/algorithms/sorting/selection-sort/__test__/SelectionSort.test.js

@@ -7,6 +7,12 @@ import {
   SortTester,
 } from '../../SortTester';
 
+// Complexity constants.
+const SORTED_ARRAY_VISITING_COUNT = 209;
+const NOT_SORTED_ARRAY_VISITING_COUNT = 209;
+const REVERSE_SORTED_ARRAY_VISITING_COUNT = 209;
+const EQUAL_ARRAY_VISITING_COUNT = 209;
+
 describe('SelectionSort', () => {
   it('should sort array', () => {
     SortTester.testSort(SelectionSort);
@@ -17,42 +23,34 @@ describe('SelectionSort', () => {
   });
 
   it('should visit EQUAL array element specified number of times', () => {
-    const expectedNumberOfVisits = 209;
-
     SortTester.testAlgorithmTimeComplexity(
       SelectionSort,
       equalArr,
-      expectedNumberOfVisits,
+      EQUAL_ARRAY_VISITING_COUNT,
     );
   });
 
   it('should visit SORTED array element specified number of times', () => {
-    const expectedNumberOfVisits = 209;
-
     SortTester.testAlgorithmTimeComplexity(
       SelectionSort,
       sortedArr,
-      expectedNumberOfVisits,
+      SORTED_ARRAY_VISITING_COUNT,
     );
   });
 
   it('should visit NOT SORTED array element specified number of times', () => {
-    const expectedNumberOfVisits = 209;
-
     SortTester.testAlgorithmTimeComplexity(
       SelectionSort,
       notSortedArr,
-      expectedNumberOfVisits,
+      NOT_SORTED_ARRAY_VISITING_COUNT,
     );
   });
 
   it('should visit REVERSE SORTED array element specified number of times', () => {
-    const expectedNumberOfVisits = 209;
-
     SortTester.testAlgorithmTimeComplexity(
       SelectionSort,
       reverseArr,
-      expectedNumberOfVisits,
+      REVERSE_SORTED_ARRAY_VISITING_COUNT,
     );
   });
 });

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');