Mira

lib/heapsort.js

@@ -1,8 +1,20 @@
+const { MinHeap } = require('./minheap');
+
 // This method uses a heap to sort an array.
-// Time Complexity:  ?
-// Space Complexity: ?
+// Time Complexity: O(logn)
+// Space Complexity: O(n)
 function heapsort(list) {
-  throw new Error('Method not implemented yet...');
+  const heap = new MinHeap();
+  const out = [];
+  let i = 0;
+
+  list.forEach(x => heap.add(x));
+
+  while (i < list.length) {
+    out[i] = heap.remove();
+    i++;
+  }
+  return out;
 };
 
 module.exports = heapsort;

lib/minheap.js

@@ -11,18 +11,25 @@ class MinHeap {
   }
 
   // This method adds a HeapNode instance to the heap
-  // Time Complexity: ?
-  // Space Complexity: ?
+  // Time Complexity: O(logn)
+  // Space Complexity: O(1)
   add(key, value = key) {
-    throw new Error("Method not implemented yet...");
+    const node = new HeapNode(key, value);
+    const i = this.store.push(node) - 1;
+    this.heapUp(i);
+    // console.log(this.store);
   }
 
   // This method removes and returns an element from the heap
   //   maintaining the heap structure
-  // Time Complexity: ?
-  // Space Complexity: ?
+  // Time Complexity: O(logn)
+  // Space Complexity: O(1)
   remove() {
-    throw new Error("Method not implemented yet...");
+    if (this.isEmpty()) return;
+    this.swap(0, this.store.length - 1);
+    const { value } = this.store.pop();
+    if (!this.isEmpty()) this.heapDown(0);
+    return value;
   }
 
 
@@ -38,26 +45,58 @@ 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(logn)
+  // Space complexity: O(1)
   heapUp(index) {
-    throw new Error("Method not implemented yet...");
+    if (index <= 0) return;
+
+    const parentIndex = this.parentIndex(index);
+    if (this.store[index].key < this.store[parentIndex].key) {
+      this.swap(index, parentIndex);
+      this.heapUp(parentIndex);
+    }
   }
 
   // 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 [leftIndex, rightIndex] = this.children(index);
+
+    if (!leftIndex && !rightIndex) return;
+
+    let min;
+    rightIndex ? min = rightIndex : min = leftIndex;
+    if ((leftIndex && rightIndex) &&
+      this.store[leftIndex].key < this.store[rightIndex].key) {
+        min = leftIndex;
+    }
+
+    if (this.store[index].key > this.store[min].key) {
+      this.swap(index, min);
+      this.heapDown(min);
+    }
+  }
+
+  children(index) {
+    let i = index * 2 + 1, j;
+    if (i >= this.store.length) i = null;
+    if (i && i < this.store.length - 1) j = i + 1;
+    return [i, j];
+  }
+
+  parentIndex(index) {
+    const i = Math.floor((index - 1) / 2);
+    return i < 0 ? 0 : i;
   }
 
   // If you want a swap method... you're welcome