Cedar-Bailey

lib/heapsort.js

@@ -1,8 +1,24 @@
+const { MinHeap } = require('./minheap');
 // This method uses a heap to sort an array.
-// Time Complexity:  ?
-// Space Complexity: ?
+// Time Complexity:  O(n log n) 
+// Space Complexity: O(n + log n) because of the length of the array and the heap storage-> O(n)
 function heapsort(list) {
-  throw new Error('Method not implemented yet...');
+  let minHeap = new MinHeap();
+
+  for (let num of list) {
+    minHeap.add(num);
+  }
+
+  let i = 0;
+  let currentMin;
+
+  while (!minHeap.isEmpty()) {
+    currentMin = minHeap.remove();
+    list[i] = currentMin;
+    i++;
+  }
+
+  return list;
 };
 
 module.exports = heapsort;

lib/minheap.js

@@ -11,18 +11,26 @@ 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) because of recursion
   add(key, value = key) {
-    throw new Error("Method not implemented yet...");
+    let newNode = new HeapNode(key, value);
+    this.store.push(newNode);
+    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) because of recursion
   remove() {
-    throw new Error("Method not implemented yet...");
+    if (this.isEmpty()) return;
+
+    this.swap(0, this.store.length - 1);
+    let minValue = this.store.pop()
+    this.heapDown(0);
+
+    return minValue.value;
   }
 
 
@@ -38,26 +46,50 @@ 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(1)
   heapUp(index) {
-    throw new Error("Method not implemented yet...");
+    let index1 = index;
+    let parentIndex = Math.floor((index - 1)/2);
+
+    while (parentIndex >= 0 && this.store[parentIndex].key > this.store[index1].key) {
+      this.swap(index1, parentIndex);
+      index1 = parentIndex;
+      parentIndex = Math.floor((index1 - 1)/2);
+    }
   }
 
   // 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...");
+    let leftChildIndex = (2 * index) + 1;
+    let rightChildIndex = (2 * index) + 2;
+    let nextRootIndex;
+
+    if (leftChildIndex < this.store.length && rightChildIndex < this.store.length) {
+      if (this.store[leftChildIndex].key > this.store[rightChildIndex].key) {
+        nextRootIndex = rightChildIndex;
+      } else {
+        nextRootIndex = leftChildIndex;
+      }
+    } else {
+      nextRootIndex = leftChildIndex;
+    }
+
+    if (nextRootIndex < this.store.length && this.store[nextRootIndex].key < this.store[index].key) {
+      this.swap(index, nextRootIndex);
+      this.heapDown(nextRootIndex);
+    }
   }
 
   // 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 = [];