Branches -- Paige

lib/heapsort.js

@@ -1,8 +1,23 @@
+const { MinHeap } = require('../lib/minheap');
+
 // This method uses a heap to sort an array.
-// Time Complexity:  ?
-// Space Complexity: ?
+// Time Complexity:  O(n log n) - first iterate over list (O(n))
+// and run .add() for each item (O(log n))
+// Space Complexity: O(1) - uses original list param to store sorted list
 function heapsort(list) {
-  throw new Error('Method not implemented yet...');
-};
+  if (list.length <= 1) return list;
+  const heap = new MinHeap();
+  const length = list.length;
+
+  for (let i = 0; i < length; i++) {
+    heap.add(list.pop());
+  }
+
+  while (!heap.isEmpty()) {
+    list.push(heap.remove());
+  }
+
+  return list;
+}
 
 module.exports = heapsort;

lib/minheap.js

@@ -11,18 +11,31 @@ class MinHeap {
   }
 
   // This method adds a HeapNode instance to the heap
-  // Time Complexity: ?
-  // Space Complexity: ?
+  // Time Complexity: O(log n)
+  // Space Complexity: O(log n)
   add(key, value = key) {
-    throw new Error("Method not implemented yet...");
+    const newNode = new HeapNode(key, value);
+    this.store.push(newNode);
+
+    if (this.store.length === 1) {
+      return;
+    } else {
+      return this.heapUp(this.store.length - 1);
+    }
   }
 
   // This method removes and returns an element from the heap
   //   maintaining the heap structure
-  // Time Complexity: ?
-  // Space Complexity: ?
+  // Time Complexity: O(log n)
+  // Space Complexity: O(log n)
   remove() {
-    throw new Error("Method not implemented yet...");
+    if (this.isEmpty()) return;
+
+    this.swap(0, this.store.length - 1);
+    const result = this.store.pop();
+    if (!this.isEmpty()) this.heapDown(0);
+
+    return result.value;
   }
 
 
@@ -38,26 +51,46 @@ class MinHeap {
   }
 
   // This method returns true if the heap is empty
-  // Time complexity: ?
-  // Space complexity: ?
+  // Time complexity: O(1)
+  // Space complexity: O(1)
   isEmpty() {
-    throw new Error("Method not implemented yet...");
+    return this.store.length == 0;
   }
 
   // This helper method takes an index and
   //  moves it up the heap, if it is less than it's parent node.
   //  It could be **very** helpful for the add method.
-  // Time complexity: ?
-  // Space complexity: ?
+  // Time complexity: O(log n)
+  // Space complexity: O(log n)
   heapUp(index) {
-    throw new Error("Method not implemented yet...");
+    let parent = Math.floor((index - 1)/2);
+    if (parent < 1) parent = 0;
+
+    if (this.store[parent].key > this.store[index].key) {
+      this.swap(parent, index);
+      return this.heapUp(parent);
+    }
   }
 
   // This helper method takes an index and 
   //  moves it up the heap if it's smaller
   //  than it's parent node.
   heapDown(index) {
-    throw new Error("Method not implemented yet...");
+    const leftChild = 2 * index + 1;
+    const rightChild = 2 * index + 2;
+
+    if (leftChild >= this.store.length || rightChild >= this.store.length) return;
+
+    if (this.store[leftChild].key > this.store[index].key
+        && this.store[rightChild].key > this.store[index].key) {
+          return;
+    } else if (this.store[leftChild].key < this.store[rightChild].key) {
+      this.swap(leftChild, index);
+      return this.heapDown(leftChild);
+    } else {
+      this.swap(rightChild, index);
+      return this.heapDown(rightChild);
+    } 
   }
 
   // If you want a swap method... you're welcome

test/heapsort.test.js

@@ -1,6 +1,7 @@
 const expect = require('chai').expect;
+const heapsort = require('../lib/heapsort');
 
-describe.skip("heapsort", function() {
+describe("heapsort", function() {
   it("sorts an empty array", function() {
     // Arrange 
     const list = [];