Leaves - Samantha

lib/heap_sort.rb

@@ -1,8 +1,24 @@
-
+require_relative "./min_heap"
 
 # This method uses a heap to sort an array.
-# Time Complexity:  ?
-# Space Complexity: ?
+# Time Complexity: On(log n)
+# Space Complexity: O(1)
 def heap_sort(list)
-  raise NotImplementedError, "Method not implemented yet..."
-end
+  size = list.length
+  heap = MinHeap.new
+
+  i=0
+  while i < size
+    heap.add(list[i])
+    i+=1
+  end
+
+  i=0
+  while i < size
+    result = heap.remove
+    list[i] = result
+    i+=1
+  end 
+
+  return list
+end

lib/min_heap.rb

@@ -1,77 +1,102 @@
 class HeapNode
   attr_reader :key, :value
-
+  
   def initialize(key, value)
     @key = key
     @value = value
   end
 end
 
 class MinHeap
-
+  
   def initialize
     @store = []
   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..."
+    #add element to the back of the array
+    @store << HeapNode.new(key, value)
+
+    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(log n)
+  # Space Complexity: O(log n)
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    return nil if @store.empty?
+
+    swap(0, @store.length - 1)
+    result = @store.pop
+
+    heap_down(0) unless @store.empty?
+    return result.value
   end
-
-
+
   # Used for Testing
   def to_s
     return "[]" if @store.empty?
-
+    
     output = "["
     (@store.length - 1).times do |index|
       output += @store[index].value + ", "
     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)
+  # Space complexity: O(1)
   def empty?
-    raise NotImplementedError, "Method not implemented yet..."
+    return nil if @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)
+  # Space complexity: O(1)
   def heap_up(index)
+    parent_index = (index-1)/2
 
+    if @store[parent_index].key > @store[index].key && index != 0
+      swap(parent_index, index)
+      heap_up(parent_index)
+    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..."
-  end
-
-  # If you want a swap method... you're welcome
+    left_child = index*2+1
+    right_child = index*2+2
+    return if @store[left_child].nil?
+
+    smaller_child = left_child
+    if @store[right_child] && (@store[right_child].key < @store[smaller_child].key)
+      smaller_child = right_child
+    end
+
+    if @store[index].key > @store[smaller_child].key
+      swap(index, smaller_child)
+      heap_down(smaller_child)
+    end
+  end 
+
+  # If you want a swap method... you're welcome :)
   def swap(index_1, index_2)
     temp = @store[index_1]
     @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 "heap_sort" do
   it "sorts an empty array" do
     # 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 
     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 
     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