Leaves - Nicky C.

lib/heap_sort.rb

@@ -1,8 +1,25 @@
-
+require_relative './min_heap'
 
 # This method uses a heap to sort an array.
-# Time Complexity:  ?
-# Space Complexity: ?
+# Time Complexity:  O(nlogn)
+# Space Complexity: O(n)
 def heap_sort(list)
-  raise NotImplementedError, "Method not implemented yet..."
+  size = list.length
+  return list if size == 0 || size == 1
+
+  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 +1,106 @@
 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(logn)
+  # Space Complexity: O(1)
   def add(key, value = key)
-    raise NotImplementedError, "Method not implemented yet..."
+    @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(logn)
+  # Space Complexity: O(1)
   def remove()
-    raise NotImplementedError, "Method not implemented yet..."
+    return nil if @store.empty?
+    return @store[0].value if @store.length == 1
+
+    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 true 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(logn)
+  # Space complexity: O(logn)
   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 
+  
+  # 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 + 1
+    right_child = index * 2 + 2
+    return if @store[left_child].nil? && @store[right_child].nil?
+
+    if @store[right_child].nil?
+      smallest_child = left_child
+    else
+      if @store[left_child].key < @store[right_child].key
+        smallest_child = left_child
+      else
+        smallest_child = right_child
+      end
+    end
+
+    if @store[index].key > @store[smallest_child].key
+      swap(smallest_child, index)
+      heap_down(smallest_child)
+    end
+    return
   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

@@ -1,35 +1,35 @@
 require_relative "test_helper"
 
-xdescribe "heapsort" do
+describe "heapsort" 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