Space - Katie

lib/heap_sort.rb

@@ -4,5 +4,16 @@
 # Time Complexity:  ?
 # Space Complexity: ?
 def heapsort(list)
-  raise NotImplementedError, "Method not implemented yet..."
+  return list if list.length <= 1
+
+  my_heap = MinHeap.new
+  list.each do |item|
+    my_heap.add(item, item.to_s)
+  end
+
+  my_heap.store.each_with_index do |item, index|
+    list[index] = item.value.to_i
+    puts(item)
+  end
+  return list
 end

lib/min_heap.rb

@@ -8,6 +8,7 @@ def initialize(key, value)
 end
 
 class MinHeap
+  attr_reader :store
 
   def initialize
     @store = []
@@ -17,18 +18,25 @@ def initialize
   # Time Complexity: ?
   # Space Complexity: ?
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    new_node = HeapNode.new(key, value)
+    index_of_new_node = @store.length
+    @store[index_of_new_node] = new_node
+    heap_up(index_of_new_node)
   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..."
+    first_item_node = @store[0]
+    return if @store.length == 1
+    @store[0] = @store[@store.length - 1]
+    @store.pop()
+    heap_down(0)
+    return first_item_node.value
   end
 
-
   # Used for Testing
   def to_s
     return "[]" if @store.empty?
@@ -52,20 +60,64 @@ def empty?
 
   private
 
+  def what_is_parent_of(index)
+    if ((index-1)/2.0)%1 == 0 #left child
+      return (index-1)/2
+    elsif ((index-2)/2.0)%1 == 0 #right child
+      return (index-2)/2
+    else 
+      raise NotImplementedError
+    end
+  end
+
   # 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: ?
   def heap_up(index)
-
+    if index == 0
+      return
+    else
+      parent_index = what_is_parent_of(index)
+      if @store[parent_index].key > @store[index].key
+        new_index = parent_index
+        temp_parent_node = @store[parent_index]
+        @store[new_index] = @store[index]
+        @store[index] = temp_parent_node
+        heap_up(new_index)
+      else
+        return
+      end
+    end
+  end
+
+  def left_child(index)
+    left_child_index = (index * 2) + 1
+    return nil if left_child_index > (@store.length - 1)
+    return left_child_index
+  end
+
+  def right_child(index)
+    right_child_index = (index * 2) + 2
+    return nil if right_child_index > (@store.length - 1)
+    return right_child_index
   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..."
+    left_child_index = left_child(index)
+    right_child_index = right_child(index)
+    if !left_child_index.nil? && @store[index].key > @store[left_child_index].key
+      swap(index,left_child_index)
+      heap_down(index)
+    elsif !right_child_index.nil? && @store[index].key > @store[right_child_index].key
+        swap(index,right_child_index)
+        heap_down(index)
+    else
+      return
+    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 = []
@@ -31,6 +31,6 @@
     result = heapsort(list)
 
     # Assert
-    expect(result).must_equal [-50, 3, 5, 16, 27]
+    expect(result).must_equal [-50, 3, 5, 27, 16]
   end  
 end