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Commit a7956bd

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Merge pull request knaxus#155 from knaxus/heaps
Heaps
2 parents 0561ee8 + 6a5e13a commit a7956bd

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2 files changed

+128
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const MaxHeap = require('.');
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describe('MaxHeap', () => {
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it('Should be a class', () => {
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expect(typeof MaxHeap.prototype.constructor).toEqual('function');
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});
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const mh = new MaxHeap();
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beforeEach(() => {
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mh.destroy();
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});
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it('Should create an instance of MaxHeap', () => {
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expect(mh instanceof MaxHeap).toEqual(true);
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});
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it('Should add an element to the MaxHeap', () => {
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mh.add(10);
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expect(mh.getMax()).toEqual(10);
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});
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it('Should keep the largest element at the root', () => {
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[12, 5, 34].forEach(el => mh.add(el));
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expect(mh.getMax()).toEqual(34);
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});
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it('Should retain Heap properties after removal of an element', () => {
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[12, 45, 1, 34].forEach(el => mh.add(el));
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expect(mh.getMax()).toEqual(45);
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mh.remove();
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expect(mh.getMax()).toEqual(34);
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});
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it('Should return `null` when heap is empty', () => {
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[1, 34].forEach(el => mh.add(el));
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expect(mh.getMax()).toEqual(34);
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mh.remove();
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mh.remove();
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expect(mh.getMax()).toEqual(null);
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});
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it('Should return the elelment value on `remove()`', () => {
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[1, 34].forEach(el => mh.add(el));
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expect(mh.getMax()).toEqual(34);
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expect(mh.remove()).toEqual(34);
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expect(mh.remove()).toEqual(1);
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expect(mh.getMax()).toEqual(null);
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});
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});
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class MaxHeap {
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constructor() {
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this.heap = [];
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}
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add(element) {
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this.heap.push(element);
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// check for the parent element & swap if required
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// eslint-disable-next-line no-underscore-dangle
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this.__traverseUpAndSwap(this.heap.length - 1);
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}
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getMax() {
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return this.heap[0] || null;
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}
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remove() {
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// return the element at the root
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const max = this.heap[0] || null;
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if (this.heap.length > 1) {
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// move the leaf to the root
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this.heap[0] = this.heap[this.heap.length - 1];
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this.heap.splice(this.heap.length - 1, 1);
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// restore the heapify property
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// eslint-disable-next-line no-underscore-dangle
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this.__heapify(0);
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return max;
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}
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if (this.heap.length === 1) {
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this.heap.splice(this.heap.length - 1, 1);
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return max;
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}
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return max;
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}
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__heapify(index) {
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const left = index * 2;
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const right = index * 2 + 1;
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let largest = index;
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if (this.heap.length > left && this.heap[largest] < this.heap[left]) {
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largest = left;
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}
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if (this.heap.length > right && this.heap[largest] < this.heap[right]) {
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largest = right;
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}
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if (largest !== index) {
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const temp = this.heap[largest];
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this.heap[largest] = this.heap[index];
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this.heap[index] = temp;
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// eslint-disable-next-line no-underscore-dangle
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this.__heapify(largest);
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}
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}
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__traverseUpAndSwap(index) {
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if (index <= 0) return;
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const parent = Math.floor(index / 2);
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if (this.heap[parent] < this.heap[index]) {
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const temp = this.heap[parent];
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this.heap[parent] = this.heap[index];
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this.heap[index] = temp;
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// eslint-disable-next-line no-underscore-dangle
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this.__traverseUpAndSwap(parent);
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}
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}
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destroy() {
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this.heap = [];
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}
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}
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module.exports = MaxHeap;

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