Erica

lib/heap_sort.rb

@@ -1,8 +1,18 @@
+# This method uses a heap to sort an array.
+# Time Complexity:  O(n log n) where n is the number of items in the list
+# Space Complexity: O(n) where n is the number of items in the list
+def heapsort(list)
+  return list if list.length < 2
+
+  heap = MinHeap.new
 
+  until list.empty?
+    heap.add(list.pop)
+  end
 
-# This method uses a heap to sort an array.
-# Time Complexity:  ?
-# Space Complexity: ?
-def heap_sort(list)
-  raise NotImplementedError, "Method not implemented yet..."
+  until heap.empty?
+    list.push(heap.remove)
+  end
+
+  return list
 end

lib/min_heap.rb

@@ -14,18 +14,30 @@ def initialize
   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 items in the heap
+  # Space Complexity: O(1)
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    node = HeapNode.new(key, value)
+
+    if @store.empty?
+      @store.push(node)
+    else
+      @store.push(node)
+      heap_up(@store.length - 1)
+    end
   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 items in the heap
+  # Space Complexity: O(1)
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    return nil if @store.empty?
+
+    swap(0, @store.length - 1)
+    removed = @store.pop
+    heap_down(0)
+    return removed.value
   end
 
 
@@ -44,28 +56,52 @@ def to_s
   end
 
   # This method returns true if the heap is empty
-  # Time complexity: ?
-  # Space complexity: ?
+  # Time complexity: O(n) where n is the number of items in the heap--
+  # although I feel like this could be made to be O(1)
+  # because we don't need to actually calcuate the length of @store,
+  # we only need to check whether it has at least one item 
+  # 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 items in the heap
+  # Space complexity: O(1)
   def heap_up(index)
-
+    return if @store[index].nil? || 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..."
+    left = (index * 2) + 1
+    right = (index * 2) + 2
+
+    return if @store[left].nil?
+
+    if !@store[right]
+      swap(index, left) if @store[index].value > @store[left].value
+      return
+    elsif !@store[right]
+      min = left
+    else
+      min = @store[left].key < @store[right].key ? left : right
+    end
+
+    swap(index, min)
+    heap_down(min)
   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 = []