Merge pull request #156 from knaxus/heaps

Heaps

Author: TheSTL

.assets/dsa.jpeg

@@ -1,3 +1,5 @@
+<img src=".assets/logo.png" align="right"/>
+
 # Problem Solving using Javascript
 
 [![Open Source Love](https://badges.frapsoft.com/os/v2/open-source.svg?v=103)](https://github.com/vinitshahdeo/HacktoberFest)
@@ -7,17 +9,20 @@
 
 Collection of interview questions with Unit Tests. Problems includes Data Structures, Logical and few Classical problems.
 
-## Table of Contents
+![DSA](.assets/dsa.jpeg)
+
+## Overview
+
+This repo contains the following sections implemented in **JavaScript**
 
-This repo contains the following in **JavaScript**
-- Data Structures
-- Algorithms
-- Logical Problems
-- Classics (Few of the classical questions)
+- [Data Structures](src/_DataStructures_)
+- [Algorithms](src/_Algorithms_)
+- [Logical Problems](src/_Problems_)
+- [Classics (Few of the classical questions)](src/_Classics_)
 
-Find the detailed Table of Contents here: [Detailed TOC](TOC.md)
+Find the detailed contents and problem list here: [Table Of Contents](TOC.md)
 
-## CONTRIBUTION Guide
+## Contribution Guide
 
 It's great to know that you want to contribute to this repo. Thanks for taking interest. please fing the [guide here](https://github.com/knaxus/problem-solving-javascript/blob/master/CONTRIBUTING.md)
 

.assets/logo.png

@@ -1,4 +1,3 @@
-
 ## Table of Contents
 
 ### Data Structures
@@ -44,6 +43,12 @@
     - [Unique words count in a Trie](src/_DataStructures_/Trees/Trie/unique-word-count)
     - [All the words from a Trie](src/_DataStructures_/Trees/Trie/all-words-in-trie)
     - [Unique words in a Trie](src/_DataStructures_/Trees/Trie/get-unique-words)
+- [Heaps](src/_DataStructures_/Heaps)
+  - [MaxHeap](src/_DataStructures_/Heaps/MaxHeap)
+  - [MinHeap](src/_DataStructures_/Heaps/MinHeap)
+  - Problems
+    - [K Largest Elements](src/_DataStructures_/Heaps/k-largest-in-array)
+    - [K Smallest Elements](src/_DataStructures_/Heaps/k-smallest-in-array)
 
 ### Logical Problems
 
@@ -75,8 +80,7 @@
 
 - [LRU Cache](src/_Algorithms_/lru-cache)
 - Path Finders
-  - [A*](src/_Algorithms_/path-finder/a-star)
-
+  - [A\*](src/_Algorithms_/path-finder/a-star)
 
 ### Classics
 

README.md

@@ -15,6 +15,11 @@ describe('MaxHeap', () => {
     expect(mh instanceof MaxHeap).toEqual(true);
   });
 
+  it('Should create a MaxHeap using collection', () => {
+    const mHBulk = new MaxHeap([1, 3, 21, 9, 101, 0]);
+    expect(mHBulk.getMax()).toEqual(101);
+  });
+
   it('Should add an element to the MaxHeap', () => {
     mh.add(10);
     expect(mh.getMax()).toEqual(10);
@@ -47,4 +52,8 @@ describe('MaxHeap', () => {
     expect(mh.remove()).toEqual(1);
     expect(mh.getMax()).toEqual(null);
   });
+
+  it('Should return `null` on `remove() called on empty heap`', () => {
+    expect(mh.getMax()).toEqual(null);
+  });
 });

TOC.md

@@ -1,6 +1,11 @@
 class MaxHeap {
-  constructor() {
+  constructor(collection) {
     this.heap = [];
+    if (collection) {
+      collection.forEach((element) => {
+        this.add(element);
+      });
+    }
   }
 
   add(element) {
@@ -11,27 +16,24 @@ class MaxHeap {
   }
 
   getMax() {
-    return this.heap[0] || null;
+    return this.heap[0] !== undefined ? this.heap[0] : null;
   }
 
   remove() {
+    const max = this.heap[0] !== undefined ? this.heap[0] : null;
     // return the element at the root
-    const max = this.heap[0] || null;
+    if (this.heap.length === 1) {
+      this.heap.pop();
+    }
+
     if (this.heap.length > 1) {
       // move the leaf to the root
       this.heap[0] = this.heap[this.heap.length - 1];
-      this.heap.splice(this.heap.length - 1, 1);
+      this.heap.pop();
       // restore the heapify property
       // eslint-disable-next-line no-underscore-dangle
       this.__heapify(0);
-      return max;
     }
-
-    if (this.heap.length === 1) {
-      this.heap.splice(this.heap.length - 1, 1);
-      return max;
-    }
-
     return max;
   }
 

src/_DataStructures_/Heaps/MaxHeap/MaxHeap.test.js

@@ -0,0 +1,59 @@
+const MinHeap = require('.');
+
+describe('MinHeap', () => {
+  it('Should be a class', () => {
+    expect(typeof MinHeap.prototype.constructor).toEqual('function');
+  });
+
+  const mh = new MinHeap();
+
+  beforeEach(() => {
+    mh.destroy();
+  });
+
+  it('Should create an instance of MinHeap', () => {
+    expect(mh instanceof MinHeap).toEqual(true);
+  });
+
+  it('Should create a MinHeap using collection', () => {
+    const mHBulk = new MinHeap([112, 3, 21, 9, 10, 0]);
+    expect(mHBulk.getMin()).toEqual(0);
+  });
+
+  it('Should add an element to the MinHeap', () => {
+    mh.add(10);
+    expect(mh.getMin()).toEqual(10);
+  });
+
+  it('Should keep the smallest element at the root', () => {
+    [12, 5, 34].forEach(el => mh.add(el));
+    expect(mh.getMin()).toEqual(5);
+  });
+
+  it('Should retain Heap properties after removal of an element', () => {
+    [12, 45, 1, 34].forEach(el => mh.add(el));
+    expect(mh.getMin()).toEqual(1);
+    mh.remove();
+    expect(mh.getMin()).toEqual(12);
+  });
+
+  it('Should return `null` when heap is empty', () => {
+    [1, 34].forEach(el => mh.add(el));
+    expect(mh.getMin()).toEqual(1);
+    mh.remove();
+    mh.remove();
+    expect(mh.getMin()).toEqual(null);
+  });
+
+  it('Should return the elelment value on `remove()`', () => {
+    [1, 34].forEach(el => mh.add(el));
+    expect(mh.getMin()).toEqual(1);
+    expect(mh.remove()).toEqual(1);
+    expect(mh.remove()).toEqual(34);
+    expect(mh.getMin()).toEqual(null);
+  });
+
+  it('Should return `null` on `remove() called on empty heap`', () => {
+    expect(mh.getMin()).toEqual(null);
+  });
+});

src/_DataStructures_/Heaps/MaxHeap/index.js

@@ -0,0 +1,78 @@
+class MinHeap {
+  constructor(collection) {
+    this.heap = [];
+
+    if (collection) {
+      collection.forEach((element) => {
+        this.add(element);
+      });
+    }
+  }
+
+  add(element) {
+    this.heap.push(element);
+    // check for the parent element & swap if required
+    // eslint-disable-next-line no-underscore-dangle
+    this.__traverseUpAndSwap(this.heap.length - 1);
+  }
+
+  getMin() {
+    return this.heap[0] !== undefined ? this.heap[0] : null;
+  }
+
+  remove() {
+    const min = this.heap[0] !== undefined ? this.heap[0] : null;
+    if (this.heap.length === 1) {
+      this.heap.pop();
+    }
+    if (this.heap.length > 1) {
+      this.heap[0] = this.heap[this.heap.length - 1];
+      this.heap.pop();
+      // eslint-disable-next-line no-underscore-dangle
+      this.__heapify(0);
+    }
+    return min;
+  }
+
+  destroy() {
+    this.heap = [];
+  }
+
+  // eslint-disable-next-line consistent-return
+  __traverseUpAndSwap(index) {
+    if (index <= 0) return null;
+
+    const parent = Math.floor(index / 2);
+
+    if (this.heap[parent] > this.heap[index]) {
+      const temp = this.heap[parent];
+      this.heap[parent] = this.heap[index];
+      this.heap[index] = temp;
+      // eslint-disable-next-line no-underscore-dangle
+      this.__traverseUpAndSwap(parent);
+    }
+  }
+
+  __heapify(index) {
+    const left = index * 2;
+    const right = index * 2 + 1;
+
+    let smallest = index;
+
+    if (this.heap.length > left && this.heap[smallest] > this.heap[left]) {
+      smallest = left;
+    }
+    if (this.heap.length > right && this.heap[smallest] > this.heap[right]) {
+      smallest = right;
+    }
+    if (smallest !== index) {
+      const tmp = this.heap[smallest];
+      this.heap[smallest] = this.heap[index];
+      this.heap[index] = tmp;
+      // eslint-disable-next-line no-underscore-dangle
+      this.__heapify(smallest);
+    }
+  }
+}
+
+module.exports = MinHeap;

src/_DataStructures_/Heaps/MinHeap/MinHeap.test.js

@@ -0,0 +1,22 @@
+const MaxHeap = require('../MaxHeap');
+
+/**
+ * Find the 4 largest elements from an array
+ */
+
+function findKLargest(collection, k) {
+  if (!collection || !Array.isArray(collection)) {
+    throw new Error('Invalid / missing collection');
+  }
+
+  // create a MaxHeap using the collection
+  const mh = new MaxHeap(collection);
+  const result = [];
+
+  for (let i = 0; i < k; i += 1) {
+    result.push(mh.remove());
+  }
+  return result;
+}
+
+module.exports = findKLargest;

src/_DataStructures_/Heaps/MinHeap/index.js

@@ -0,0 +1,21 @@
+/**
+ * Find 4 smallest elements in an array
+ */
+
+const MinHeap = require('../MinHeap');
+
+function findKSmallest(collection, k) {
+  if (!collection || !Array.isArray(collection)) {
+    throw new Error('Invalid / missing collection');
+  }
+
+  // create a MinHeap using the collection
+  const mh = new MinHeap(collection);
+  const result = [];
+  for (let i = 0; i < k; i += 1) {
+    result.push(mh.remove());
+  }
+  return result;
+}
+
+module.exports = findKSmallest;