Dani - Leaves

lib/heap_sort.rb

@@ -1,8 +1,20 @@
-
+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..."
+# Time Complexity:  O(n)
+# Space Complexity: O(n)
+def heapsort(list)
+  heap = MinHeap.new()
+
+  list.each do |element|
+    heap.add(element)
+  end
+
+  result = []
+  while !heap.empty?
+    node = heap.remove
+    result.push(node)
+  end
+
+  return result
 end

lib/min_heap.rb

@@ -14,18 +14,28 @@ def initialize
   end
 
   # This method adds a HeapNode instance to the heap
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: O(1)
+  # Space Complexity: O(1)
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    new_node = HeapNode.new(key, value)
+    @store.push(new_node)
+
+    index = @store.length - 1
+    heap_up(index)
   end
 
   # This method removes and returns an element from the heap
   #   maintaining the heap structure
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    if [email protected]?
+      del = @store.first
+      @store[0] = @store.last
+      @store = @store[0...-1]
+      heap_down(0)
+    end
+    return del.value
   end
 
 
@@ -44,28 +54,56 @@ def to_s
   end
 
   # This method returns true if the heap is empty
-  # Time complexity: ?
-  # Space complexity: ?
+  # Time complexity: O(1)
+  # Space complexity: O(1)
   def empty?
-    raise NotImplementedError, "Method not implemented yet..."
+    return @store.empty?
   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(1)
+  # Space complexity: O(1)
   def heap_up(index)
-
+    i = index
+
+    while i != 0 
+      parent_i = get_parent_index(i) 
+      p_node =  @store[parent_i]
+      a_node = @store[i]
+      if p_node.key > a_node.key
+        swap(parent_i, i) 
+      end 
+      i = parent_i
+    end
+  end
+
+  def get_parent_index(index)
+    return (index - 1) / 2
   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_i = index * 2 + 1
+    right_i = index * 2 + 2
+
+    if right_i < @store.length
+      min_child = @store[left_i].key < @store[right_i].key ? left_i : right_i
+
+      if @store[index].key > @store[min_child].key
+        swap(index, min_child)
+        heap_down(min_child)
+      end
+    elsif left_i < @store.length
+      if @store[index].key > @store[left_i].key
+        swap(index, left_i)
+      end
+    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 = []