Amy W

lib/heap_sort.rb

@@ -1,8 +1,20 @@
-
-
+require_relative "./min_heap.rb"
 # This method uses a heap to sort an array.
-# Time Complexity:  ?
-# Space Complexity: ?
+# Time Complexity: O(n(log(n)) where n is the length of the list
+# Space Complexity: O(n) where n is the length of the list
 def heap_sort(list)
-  raise NotImplementedError, "Method not implemented yet..."
-end
+  sorted_list = []
+
+  if list.length < 2
+    return list
+  else
+    heap = MinHeap.new()
+
+    list.each { |list_item| heap.add(list_item) }
+
+    while !heap.empty?
+      sorted_list << heap.remove()
+    end
+    return sorted_list
+  end
+end

lib/min_heap.rb

@@ -8,26 +8,34 @@ def initialize(key, value)
 end
 
 class MinHeap
-
   def initialize
     @store = []
   end
 
   # This method adds a HeapNode instance to the heap
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: O(logn) where n is the length of the heap
+  # Space Complexity: 0(logn)
   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: ?
+  # Time Complexity: O(logn) where n is the length of the heap
+  # Space Complexity: 0(logn)
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
-  end
+    if @store.empty?
+      return nil
+    end
 
+    swap(0, @store.length - 1)
+    result = @store.pop
+
+    heap_down(0) unless @store.empty?
+    return result.value
+  end
 
   # Used for Testing
   def to_s
@@ -39,33 +47,57 @@ def to_s
     end
 
     output += @store.last.value + "]"
-      
+
     return output
   end
 
   # This method returns true if the heap is empty
-  # Time complexity: ?
-  # Space complexity: ?
+  # Time complexity: O(n) where n is the length of @store
+  # Space complexity: O(1)
   def empty?
-    raise NotImplementedError, "Method not implemented yet..."
+    return @store.length == 0
   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) where n is the length of the heap
+  # Space Complexity: 0(logn)
   def heap_up(index)
-
+    parent_node_index = index.odd? ? (index - 1) / 2 : (index - 2) / 2
+
+    if @store[index].key >= @store[parent_node_index].key || index == 0
+      return
+    else
+      swap(index, parent_node_index)
+      heap_up(parent_node_index)
+    end
   end
 
-  # This helper method takes an index and 
+  # 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 = 2 * index + 1
+    right_child = 2 * index + 2
+
+    if @store[left_child] == nil
+      return
+    elsif @store[right_child] == nil && @store[index].key > @store[left_child].key
+      swap(index, left_child)
+      return
+    elsif @store[right_child] == nil
+      return
+    else
+      min_child = @store[right_child].key < @store[left_child].key ? right_child : left_child
+
+      if @store[index].key > @store[min_child].key
+        swap(index, min_child)
+        heap_down(min_child)
+      end
+    end
   end
 
   # If you want a swap method... you're welcome
@@ -74,4 +106,4 @@ def swap(index_1, index_2)
     @store[index_1] = @store[index_2]
     @store[index_2] = temp
   end
-end
+end

test/heapsort_test.rb

@@ -1,36 +1,36 @@
 require_relative "test_helper"
 
-xdescribe "heapsort" do
+describe "heap_sort" do
   it "sorts an empty array" do
-    # Arrange 
+    # Arrange
     list = []
 
     # Act
-    result = heapsort(list)
+    result = heap_sort(list)
 
     # Assert
     expect(result).must_equal []
   end
 
   it "can sort a 1-element array" do
-    # Arrange 
+    # Arrange
     list = [5]
 
     # Act
-    result = heapsort(list)
+    result = heap_sort(list)
 
     # Assert
     expect(result).must_equal [5]
   end
-  
+
   it "can sort a 5-element array" do
-    # Arrange 
+    # Arrange
     list = [5, 27, 3, 16, -50]
 
     # Act
-    result = heapsort(list)
+    result = heap_sort(list)
 
     # Assert
     expect(result).must_equal [-50, 3, 5, 16, 27]
-  end  
-end
+  end
+end

test/min_heap_test.rb

@@ -1,9 +1,9 @@
 require_relative "test_helper"
 
 describe "Heap" do
-  let(:heap) {MinHeap.new}
+  let(:heap) { MinHeap.new }
   it "can be created" do
-    
+
     # Assert
     expect(heap).must_be_instance_of MinHeap
   end
@@ -52,30 +52,30 @@
   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
+    # Another Act
+    removed = heap.remove
 
-  # Another assert
-  expect(removed).must_equal "Pasta"
+    # Another assert
+    expect(removed).must_equal "Pasta"
   end
-end
+end