Evelynn

lib/heap_sort.rb

@@ -1,8 +1,24 @@
-
+require_relative "./min_heap"
+require "pry"
 
 # This method uses a heap to sort an array.
-# Time Complexity:  ?
-# Space Complexity: ?
-def heap_sort(list)
-  raise NotImplementedError, "Method not implemented yet..."
-end
+# Time Complexity:  O (n log n) where n is the number of items in the list. The two loops are O(n) and adding/removing from a heap is O (log n). Inserting/removing from an array is O(n).
+# Space Complexity: O(n) where n is the number of items in the list because you are creating a new heap that needs to store n number of items.
+def heapsort(list)
+  heap = MinHeap.new
+  counter = list.length
+
+  # Remove each item from array and add to heap
+  counter.times do
+    node = list.pop
+    heap.add(node)
+  end
+
+  # Remove each item from heap and add back to array
+  counter.times do
+    element = heap.remove
+    list.push(element)
+  end
+
+  return list
+end

lib/min_heap.rb

@@ -8,26 +8,32 @@ 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(log n) where n is the number of elements in the heap
+  # Space Complexity: O(1)
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    new_node = HeapNode.new(key, value)
+    @store << new_node
+
+    return if @store.length < 2
+    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(log n) where n is the number of elements in the heap
+  # Space Complexity: O(1)
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
-  end
+    swap(0, @store.length - 1)
+    root_value = @store.pop.value
 
+    heap_down(0)
+    return root_value
+  end
 
   # Used for Testing
   def to_s
@@ -39,33 +45,55 @@ 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 number of elements in the array
+  # 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(log n) where n is the number of elements in the heap
+  # 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(parent_index, index)
+      return heap_up(parent_index)
+    else
+      return
+    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_i = index * 2 + 1
+    right_child_i = index * 2 + 2
+    return if @store[left_child_i] == nil
+
+    # Find smaller child.
+    smaller_child_i = left_child_i
+    if @store[right_child_i] != nil
+      smaller_child_i = (@store[left_child_i].key <= @store[right_child_i].key) ? left_child_i : right_child_i
+    end
+
+    if @store[index].key > @store[smaller_child_i].key
+      swap(index, smaller_child_i)
+      return heap_down(smaller_child_i)
+    else 
+      return
+    end
   end
 
   # If you want a swap method... you're welcome
@@ -74,4 +102,4 @@ def swap(index_1, index_2)
     @store[index_1] = @store[index_2]
     @store[index_2] = temp
   end
-end
+end

test/heapsort_test.rb

@@ -1,8 +1,9 @@
 require_relative "test_helper"
+require "pry"
 
-xdescribe "heapsort" do
+describe "heapsort" do
   it "sorts an empty array" do
-    # Arrange 
+    # Arrange
     list = []
 
     # Act
@@ -13,7 +14,7 @@
   end
 
   it "can sort a 1-element array" do
-    # Arrange 
+    # Arrange
     list = [5]
 
     # Act
@@ -22,15 +23,16 @@
     # Assert
     expect(result).must_equal [5]
   end
-  
+
   it "can sort a 5-element array" do
-    # Arrange 
+    # Arrange
     list = [5, 27, 3, 16, -50]
 
     # Act
+    # binding.pry
     result = heapsort(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