Margaret

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: ?
-def heap_sort(list)
-  raise NotImplementedError, "Method not implemented yet..."
-end
+# Time Complexity:  O(nlogn)
+# Space Complexity: O(n)
+def heapsort(list)
+  return list if list.length == 0 || list.length == 1
+
+  #create new instance of MinHeap
+  min_heap = MinHeap.new
+
+  #add all the elements from list
+  list.each do |element|
+    min_heap.add(element, value = element)
+  end
+
+  #remove and add to result
+  result = []
+  list.length.times do
+    result << min_heap.remove
+  end
+  return result
+end

lib/min_heap.rb

@@ -8,27 +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)
+  # Space Complexity: constant
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    heap_node = HeapNode.new(key, value)
+    @store.push(heap_node)
+    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)
+  # Space Complexity: constant
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    # raise NotImplementedError, "Method not implemented yet..."
+    #swap element to be removed with the last element
+    swap(0, @store.length - 1)
+    answer = @store.pop
+    heap_down(0)
+    return answer.value
   end
 
-
   # Used for Testing
   def to_s
     return "[]" if @store.empty?
@@ -39,7 +44,7 @@ def to_s
     end
 
     output += @store.last.value + "]"
-      
+
     return output
   end
 
@@ -55,17 +60,40 @@ def empty?
   # 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)
+  # Space complexity: constant
   def heap_up(index)
-
+    return if index == 0
+    parent_index = (index - 1) / 2
+    return if @store[parent_index].key < @store[index].key
+    swap(index, parent_index)
+    heap_up(parent_index)
   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..."
+    # raise NotImplementedError, "Method not implemented yet..."
+    left_child = index * 2 + 1
+    right_child = index * 2 + 2
+    if @store[left_child] == nil #at bottom of tree
+      return
+    end
+    if @store[right_child] == nil
+      if @store[index].value > @store[left_child].value
+        swap(index, left_child)
+      end
+      return
+    end
+
+    if @store[left_child].key < @store[right_child].key
+      swap(left_child, index)
+      heap_down(left_child)
+    else
+      swap(right_child, index)
+      heap_down(right_child)
+    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

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