Sarah

lib/heap_sort.rb

@@ -1,8 +1,22 @@
 
 
 # This method uses a heap to sort an array.
-# Time Complexity:  ?
-# Space Complexity: ?
+# Time Complexity:  0(n log n) where n is the length of the list. heapify iterates through the list and for each calls add() which is 0(log n) so thats n log n for heapify, heap sort is the same, n log n. So total its 0(2 * nlogn) which reduces to n log n
+# Space Complexity: 0(1), we create a new heap, but each time we add one, we remove one from the list. and then westart moving items one at a time back to the list. the length of the heap and the length of the list combined are always equal to the original list size, so we dont actually use any extra space.
 def heap_sort(list)
-  raise NotImplementedError, "Method not implemented yet..."
-end
+  heap = heapify(list)
+  until heap.empty?
+    item = heap.remove()
+    list.append(item)
+  end
+  return list
+end
+
+def heapify(list)
+  heap = MinHeap.new()
+  until list.empty?
+    item = list.pop()
+    heap.add(item)
+  end
+  return heap
+end

lib/min_heap.rb

@@ -8,27 +8,35 @@ def initialize(key, value)
 end
 
 class MinHeap
-
   def initialize
     @store = []
   end
 
   # This method adds a HeapNode instance to the heap
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: 0(log n) where n is the length of @store, everything is constant besides heap_up() which is 0(log n)
+  # Space Complexity: 0(1) constant sized variables
+
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    @store.append(HeapNode.new(key, value))
+    curr = @store.length - 1
+
+    curr = heap_up(curr)
   end
 
   # This method removes and returns an element from the heap
   #   maintaining the heap structure
-  # Time Complexity: ?
-  # Space Complexity: ?
+  # Time Complexity: 0(log n) where n is the length of @store, everything is constant besides heap_down() which is 0(log n)
+  # Space Complexity: 0(1) constant sized variables
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    return if @store.empty?
+    last = @store.length - 1
+    curr = 0
+    swap(last, curr)
+    removed = @store.pop
+    heap_down(curr)
+    return removed.value
   end
 
-
   # Used for Testing
   def to_s
     return "[]" if @store.empty?
@@ -39,33 +47,47 @@ def to_s
     end
 
     output += @store.last.value + "]"
-      
+
     return output
   end
 
   # This method returns true if the heap is empty
-  # Time complexity: ?
-  # Space complexity: ?
+  # Time complexity: O(1) Length and empty are constant time in ruby, not enumerables.
+  # Space complexity: O(1) no variables created at all
   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(log n) where n is the index
+  # Space complexity: O(1) only use constant sized variables
   def heap_up(index)
-
+    until index == 0 || @store[index].key >= @store[((index - 1) / 2)].key
+      parent = (index - 1) / 2
+      swap(parent, index) if @store[parent].key > @store[index].key
+      index = parent
+    end
   end
 
-  # This helper method takes an index and 
+  # 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..."
+    until (index * 2 + 1) > @store.length - 1
+      left = index * 2 + 1
+      right = index * 2 + 2
+      if right > @store.length - 1
+        child = left
+      else
+        child = @store[left].key < @store[right].key ? left : right
+      end
+      @store[index].key > @store[child].key ? swap(index, child) : return
+    end
+    return
   end
 
   # If you want a swap method... you're welcome
@@ -74,4 +96,4 @@ def swap(index_1, index_2)
     @store[index_1] = @store[index_2]
     @store[index_2] = temp
   end
-end
+end

test/heapsort_test.rb

@@ -1,36 +1,36 @@
 require_relative "test_helper"
 
-xdescribe "heapsort" do
+describe "heapsort" do
   it "sorts an empty array" do
-    # Arrange 
+    # Arrange
     list = []
 
     # Act
-    result = heapsort(list)
+    result = heap_sort(list)
 
     # Assert
     expect(result).must_equal []
   end
 
   it "can sort a 1-element array" do
-    # Arrange 
+    # Arrange
     list = [5]
 
     # Act
-    result = heapsort(list)
+    result = heap_sort(list)
 
     # Assert
     expect(result).must_equal [5]
   end
-  
+
   it "can sort a 5-element array" do
-    # Arrange 
+    # Arrange
     list = [5, 27, 3, 16, -50]
 
     # Act
-    result = heapsort(list)
+    result = heap_sort(list)
 
     # Assert
     expect(result).must_equal [-50, 3, 5, 16, 27]
-  end  
-end
+  end
+end

test/min_heap_test.rb

@@ -1,9 +1,9 @@
 require_relative "test_helper"
 
 describe "Heap" do
-  let(:heap) {MinHeap.new}
+  let(:heap) { MinHeap.new }
   it "can be created" do
-    
+
     # Assert
     expect(heap).must_be_instance_of MinHeap
   end
@@ -52,30 +52,30 @@
   end
 
   it "can remove nodes in the proper order" do
-   # Arrange
-   heap.add(3, "Pasta")
-   heap.add(6, "Soup")
-   heap.add(1, "Pizza")
-   heap.add(0, "Donuts")
-   heap.add(16, "Cookies")
-   heap.add(57, "Cake")
+    # Arrange
+    heap.add(3, "Pasta")
+    heap.add(6, "Soup")
+    heap.add(1, "Pizza")
+    heap.add(0, "Donuts")
+    heap.add(16, "Cookies")
+    heap.add(57, "Cake")
 
-   # Act
-   removed = heap.remove
+    # Act
+    removed = heap.remove
 
-   # Assert
-   expect(removed).must_equal "Donuts"
+    # Assert
+    expect(removed).must_equal "Donuts"
 
-   # Another Act
-   removed = heap.remove
+    # Another Act
+    removed = heap.remove
 
-   # Another assert
-   expect(removed).must_equal "Pizza"
+    # Another assert
+    expect(removed).must_equal "Pizza"
 
-  # Another Act
-  removed = heap.remove
+    # Another Act
+    removed = heap.remove
 
-  # Another assert
-  expect(removed).must_equal "Pasta"
+    # Another assert
+    expect(removed).must_equal "Pasta"
   end
-end
+end