Ngoc L

lib/heap_sort.rb

@@ -1,8 +1,17 @@
 
-
+require 'min_heap.rb'
 # This method uses a heap to sort an array.
 # Time Complexity:  ?
 # Space Complexity: ?
-def heap_sort(list)
-  raise NotImplementedError, "Method not implemented yet..."
+def heapsort(list)
+  return [] if list.empty?
+  min_heap = MinHeap.new
+  list.each do |num|
+    min_heap.add(num)
+  end
+  sorted_array = []
+  while !min_heap.empty?
+    sorted_array << min_heap.remove()
+  end
+  return sorted_array
 end

lib/min_heap.rb

@@ -14,18 +14,23 @@ def initialize
   end
 
   # This method adds a HeapNode instance to the heap
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: O(logn) adding element to end of array is O(1) while heap-up worst case is O(logn)
+  # 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)
+    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(logn)
+  # Space Complexity: O(1)
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    swap(0,@store.length - 1)
+    result = @store.pop
+    heap_down(0)
+    return result.value
   end
 
 
@@ -44,28 +49,64 @@ 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.length == 0) ? true : false
   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(1)
   def heap_up(index)
 
+    if index.odd?
+      parent_index = (index-1)/2
+    else
+      parent_index = (index-2)/2
+    end
+    while @store[index].key < @store[parent_index].key && parent_index > -1
+      swap(index,parent_index)
+      index = parent_index
+      if index.odd?
+        parent_index = (index-1)/2
+      else
+        parent_index = (index-2)/2
+      end
+    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..."
+
+    left_child_index = 2 * index + 1 
+    right_child_index = 2 * index + 2
+
+    if @store[left_child_index].nil?
+      return nil
+    end
+    if @store[right_child_index].nil?
+      if @store[index].key > @store[left_child_index].key
+        swap(index, left_child_index)
+      end
+      return
+    end
+      #  If both child exist, compare their key find min and compare to parent, swap if parent is smaller
+
+    if @store[left_child_index].key < @store[right_child_index].key
+      swap(left_child_index, index)
+      heap_down(left_child_index)
+    else
+      swap(right_child_index, index)
+      heap_down(left_child_index)
+    end
+
   end
 
   # If you want a swap method... you're welcome
@@ -74,4 +115,5 @@ def swap(index_1, index_2)
     @store[index_1] = @store[index_2]
     @store[index_2] = temp
   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 = []