Space - Stephanie

lib/heap_sort.rb

@@ -1,8 +1,23 @@
-
+# require_relative "min_heap"
 
 # This method uses a heap to sort an array.
-# Time Complexity:  ?
-# Space Complexity: ?
+# Time Complexity:  O(nlogn)
+# Space Complexity: O(1)
 def heapsort(list)
-  raise NotImplementedError, "Method not implemented yet..."
+
+  return list if list.length - 1 <= 1
+
+  heap = MinHeap.new
+
+  list.each do |value|
+    heap.add(value)
+  end
+
+  result = []
+
+  list.length.times do
+    result << heap.remove
+  end
+
+  return result
 end

lib/min_heap.rb

@@ -14,18 +14,26 @@ def initialize
   end
 
   # This method adds a HeapNode instance to the heap
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: O(logn)
+  # Space Complexity: O(1)
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    @store << HeapNode.new(key, value)
+    heap_up(@store.length - 1)
   end
 
   # This method removes and returns an element from the heap
   #   maintaining the heap structure
   # Time Complexity: ?
   # Space Complexity: ?
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    return nil if @store.empty?
+
+    swap(0, @store.length - 1)
+    result = @store.pop
+    heap_down(0)
+    return result.value
+
+
   end
 
 
@@ -44,28 +52,52 @@ def to_s
   end
 
   # This method returns true if the heap is empty
-  # Time complexity: ?
-  # Space complexity: ?
+  # Time complexity: O(1)
+  # Space complexity: O(1)
   def empty?
-    raise NotImplementedError, "Method not implemented yet..."
+    return if @store.empty? 
   end
 
   private
 
   # 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)
   def heap_up(index)
-
+    return if index == 0 
+    parent_index = (index - 1) / 2
+    if @store[parent_index].key > @store[index].key
+      swap(index, parent_index)
+      heap_up(parent_index)
+    end
   end
 
   # This helper method takes an index and 
   #  moves it up the heap if it's smaller
   #  than it's parent node.
   def heap_down(index)
-    raise NotImplementedError, "Method not implemented yet..."
+    return if index >= @store.length - 1
+
+    left_index = index * 2 + 1
+    right_index = index * 2 + 2
+
+    return if !@store[left_index] && !@store[right_index]
+
+    smallest = left_index
+
+    if left_index
+      if (right_index < @store.length) && (@store[right_index].key < @store[left_index].key)
+        smallest = right_index
+      end
+
+      if @store[smallest].key < @store[index].key
+        swap(index, smallest)
+      end
+      heap_down(smallest)
+    end
+
   end
 
   # If you want a swap method... you're welcome

test/heapsort_test.rb

@@ -1,6 +1,6 @@
 require_relative "test_helper"
 
-xdescribe "heapsort" do
+describe "heapsort" do
   it "sorts an empty array" do
     # Arrange 
     list = []

test/min_heap_test.rb

@@ -52,25 +52,25 @@
   end
 
   it "can remove nodes in the proper order" do
-   # Arrange
-   heap.add(3, "Pasta")
-   heap.add(6, "Soup")
-   heap.add(1, "Pizza")
-   heap.add(0, "Donuts")
-   heap.add(16, "Cookies")
-   heap.add(57, "Cake")
+    # Arrange
+    heap.add(3, "Pasta")
+    heap.add(6, "Soup")
+    heap.add(1, "Pizza")
+    heap.add(0, "Donuts")
+    heap.add(16, "Cookies")
+    heap.add(57, "Cake")
 
-   # Act
-   removed = heap.remove
+    # Act
+    removed = heap.remove
 
-   # Assert
-   expect(removed).must_equal "Donuts"
+    # Assert
+    expect(removed).must_equal "Donuts"
 
-   # Another Act
-   removed = heap.remove
+    # Another Act
+    removed = heap.remove
 
-   # Another assert
-   expect(removed).must_equal "Pizza"
+    # Another assert
+    expect(removed).must_equal "Pizza"
 
   # Another Act
   removed = heap.remove