Fire - Noor

lib/heap_sort.rb

@@ -1,8 +1,17 @@
 
 
 # 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 log n)
+# Space Complexity: O(n)
+def heapsort(list)
+  heap = MinHeap.new
+  result = []
+
+  list.each {|element| heap.add(element)}
+
+  until heap.empty?
+    result << heap.remove
+  end
+
+  return result
 end

lib/min_heap.rb

@@ -14,18 +14,29 @@ def initialize
   end
 
   # This method adds a HeapNode instance to the heap
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: O(log n)
+  # Space Complexity: O(log n)
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    @store << HeapNode.new(key, value)
+    heap_up(@store.length - 1) # move the new added node up (swap with parent only)
   end
 
+  #This method removes and returns the smallest keyed value from the heap.
   # This method removes and returns an element from the heap
+  #This method removes and returns the smallest keyed value from the heap.
   #   maintaining the heap structure
-  # Time Complexity: ?
-  # Space Complexity: ?
-  def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+  # Time Complexity: O(log n)
+  # Space Complexity: O(log n)
+  def remove() # removing the first
+    return nil if @store.empty?
+
+    swap(0, @store.length - 1) # swap the last element with the root
+    removed = @store.pop
+
+    heap_down(0) unless @store.empty?
+
+    removed.value
+
   end
 
 
@@ -44,28 +55,52 @@ 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..."
+    @store.empty?
   end
 
   private
 
+  # down to up
   # This helper method takes an index and
-  #  moves it up the heap, if it is less than it's parent node.
+  #  moves it up the heap, if it is less than its parent node.
   #  It could be **very** helpful for the add method.
-  # Time complexity: ?
-  # Space complexity: ?
-  def heap_up(index)
-
+  # Time complexity: O(logn)
+  # Space complexity: O(1)
+  def heap_up(index) # move the current index up to the parent and do the needed changes
+    parent = (index - 1 ) / 2
+
+    if index == 0
+      return
+    elsif @store[index].key < @store[parent].key
+      swap(parent,index)
+      heap_up(parent) # keep pushing the parent up till it's  < @store[index].key
+    end
   end
 
+  # up to down
+  # this method takes the parent(root) and 'heap it down' to it's right place
   # 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 = (index * 2) + 1 # odd is left child
+    right_child = (index * 2) + 2 # even is right child
+
+    if left_child >= @store.length # reached the limit
+      return
+      # if right child < parent AND
+      # if right child < left
+    elsif @store[right_child] && @store[right_child].key < @store[left_child].key && @store[right_child].key < @store[index].key
+      swap(right_child, index)
+      heap_down(right_child)
+      # if left child < parent
+    elsif @store[left_child].key < @store[index].key
+      swap(left_child, index)
+      heap_down(left_child)
+    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 = []