Fire - Jing

lib/heap_sort.rb

@@ -1,8 +1,18 @@
 
-
 # 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.empty?
+  heap = MinHeap.new
+
+  list.each do |n|
+    heap.add(n)
+  end
+
+  list.length.times do |i|
+    list[i] = heap.remove
+  end
+
+  return list
+end

lib/min_heap.rb

@@ -8,24 +8,33 @@ def initialize(key, value)
 end
 
 class MinHeap
+  attr_reader :store
 
   def initialize
     @store = []
   end
 
   # This method adds a HeapNode instance to the heap
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: O(logn)
+  # Space Complexity: O(1)
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    new_i = @store.length
+    @store[new_i] = HeapNode.new(key, value)
+    heap_up(new_i)
+    return key
   end
 
   # This method removes and returns an element from the heap
   #   maintaining the heap structure
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: O(logn)
+  # Space Complexity: O(1)
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    value = @store[0].value
+
+    swap(0, -1)
+    @store.delete_at(-1)
+    heap_down(0)
+    return value
   end
 
 
@@ -44,28 +53,39 @@ def to_s
   end
 
   # This method returns true if the heap is empty
-  # Time complexity: ?
-  # Space complexity: ?
+  # Time complexity: O(0)
+  # Space complexity: O(0)
   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(logn)
+  # Space complexity: O(0)
   def heap_up(index)
-
+    while index > 0 && @store[index].key < @store[(index - 1)/2].key
+      swap(index, (index - 1)/2)
+      index = (index - 1)/2
+      return if index == 0
+    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..."
+    if @store[index * 2 + 1] != nil
+      while @store[index].key > @store[index * 2 + 1].key
+        swap(index, index * 2 + 1)
+        swap(index, index * 2 + 2) if @store[index * 2 + 2] != nil && @store[index].key > @store[index * 2 + 2].key
+        index = index * 2 + 1
+        return if @store[index * 2 + 1].nil?
+      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 = []