Merge pull request knaxus#155 from knaxus/heaps

Heaps

Author: TheSTL

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

@@ -0,0 +1,50 @@
+const MaxHeap = require('.');
+
+describe('MaxHeap', () => {
+  it('Should be a class', () => {
+    expect(typeof MaxHeap.prototype.constructor).toEqual('function');
+  });
+
+  const mh = new MaxHeap();
+
+  beforeEach(() => {
+    mh.destroy();
+  });
+
+  it('Should create an instance of MaxHeap', () => {
+    expect(mh instanceof MaxHeap).toEqual(true);
+  });
+
+  it('Should add an element to the MaxHeap', () => {
+    mh.add(10);
+    expect(mh.getMax()).toEqual(10);
+  });
+
+  it('Should keep the largest element at the root', () => {
+    [12, 5, 34].forEach(el => mh.add(el));
+    expect(mh.getMax()).toEqual(34);
+  });
+
+  it('Should retain Heap properties after removal of an element', () => {
+    [12, 45, 1, 34].forEach(el => mh.add(el));
+    expect(mh.getMax()).toEqual(45);
+    mh.remove();
+    expect(mh.getMax()).toEqual(34);
+  });
+
+  it('Should return `null` when heap is empty', () => {
+    [1, 34].forEach(el => mh.add(el));
+    expect(mh.getMax()).toEqual(34);
+    mh.remove();
+    mh.remove();
+    expect(mh.getMax()).toEqual(null);
+  });
+
+  it('Should return the elelment value on `remove()`', () => {
+    [1, 34].forEach(el => mh.add(el));
+    expect(mh.getMax()).toEqual(34);
+    expect(mh.remove()).toEqual(34);
+    expect(mh.remove()).toEqual(1);
+    expect(mh.getMax()).toEqual(null);
+  });
+});

src/_DataStructures_/Heaps/MaxHeap/index.js

@@ -0,0 +1,78 @@
+class MaxHeap {
+  constructor() {
+    this.heap = [];
+  }
+
+  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);
+  }
+
+  getMax() {
+    return this.heap[0] || null;
+  }
+
+  remove() {
+    // return the element at the root
+    const max = this.heap[0] || null;
+    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);
+      // 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;
+  }
+
+  __heapify(index) {
+    const left = index * 2;
+    const right = index * 2 + 1;
+    let largest = index;
+
+    if (this.heap.length > left && this.heap[largest] < this.heap[left]) {
+      largest = left;
+    }
+
+    if (this.heap.length > right && this.heap[largest] < this.heap[right]) {
+      largest = right;
+    }
+
+    if (largest !== index) {
+      const temp = this.heap[largest];
+      this.heap[largest] = this.heap[index];
+      this.heap[index] = temp;
+      // eslint-disable-next-line no-underscore-dangle
+      this.__heapify(largest);
+    }
+  }
+
+  __traverseUpAndSwap(index) {
+    if (index <= 0) return;
+    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);
+    }
+  }
+
+  destroy() {
+    this.heap = [];
+  }
+}
+
+module.exports = MaxHeap;