Branches - Julia Bouvier

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:  n(log(n))
+# Space Complexity: O(1)
+def heapsort(list)
+  heap = MinHeap.new
+
+  until list.empty?
+    heap.add(list.pop)
+  end
+
+  index = 0
+  until heap.empty?
+    list[index] = heap.remove()
+    index += 1
+  end
+  return list
 end

lib/min_heap.rb

@@ -14,18 +14,24 @@ def initialize
   end
 
   # This method adds a HeapNode instance to the heap
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: log(n)
+  # Space Complexity: log(n)
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    @store << HeapNode.new(key, value)
+    return 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: log(n)
+  # Space Complexity: log(n)
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    return nil if @store.empty?
+    swap(0, @store.length - 1)
+
+    removed = @store.pop
+    heap_down(0) unless @store.empty?
+    return removed.value
   end
 
 
@@ -44,28 +50,51 @@ def to_s
   end
 
   # This method returns true if the heap is empty
-  # Time complexity: ?
-  # Space complexity: ?
+  # Time complexity: O(n)
+  # Space complexity: O(1)
   def empty?
-    raise NotImplementedError, "Method not implemented yet..."
+    return true if @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: log(n)
+  # Space complexity: log(n)
   def heap_up(index)
-
+    parent_index = (index - 1) / 2
+    return nil if @store.empty?
+    return if index == 0 || @store[index].key >= @store[parent_index].key
+
+    swap(index, parent_index)
+    return heap_up(parent_index)
   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..."
+    lc_index = index * 2 + 1
+    rc_index = index * 2 + 2
+    return if @store[lc_index].nil? && @store[rc_index].nil?
+    return if index == @store.length - 1
+
+    if @store[rc_index].nil? && @store[lc_index].key <= @store[index].key
+      return swap(index, lc_index)
+    elsif @store[rc_index].nil? && @store[lc_index].key > @store[index].key
+      return
+    end
+
+    return unless @store[lc_index].key <= @store[index].key && @store[rc_index].key <= @store[index].key
+    if @store[lc_index].key <= @store[rc_index].key
+      swap(index, lc_index)
+      return heap_down(lc_index)
+    else
+      swap(index, rc_index)
+      return heap_down(rc_index)
+    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 = []