diff --git a/lib/heap_sort.rb b/lib/heap_sort.rb index c8a32a4..40abd5c 100644 --- a/lib/heap_sort.rb +++ b/lib/heap_sort.rb @@ -1,8 +1,20 @@ - - +require_relative "./min_heap.rb" # This method uses a heap to sort an array. -# Time Complexity: ? -# Space Complexity: ? +# Time Complexity: O(n(log(n)) where n is the length of the list +# Space Complexity: O(n) where n is the length of the list def heap_sort(list) - raise NotImplementedError, "Method not implemented yet..." -end \ No newline at end of file + sorted_list = [] + + if list.length < 2 + return list + else + heap = MinHeap.new() + + list.each { |list_item| heap.add(list_item) } + + while !heap.empty? + sorted_list << heap.remove() + end + return sorted_list + end +end diff --git a/lib/min_heap.rb b/lib/min_heap.rb index 6eaa630..7ea30e7 100644 --- a/lib/min_heap.rb +++ b/lib/min_heap.rb @@ -8,26 +8,34 @@ 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: O(logn) where n is the length of the heap + # Space Complexity: 0(logn) 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) where n is the length of the heap + # Space Complexity: 0(logn) def remove() - raise NotImplementedError, "Method not implemented yet..." - end + if @store.empty? + return nil + end + swap(0, @store.length - 1) + result = @store.pop + + heap_down(0) unless @store.empty? + return result.value + end # Used for Testing def to_s @@ -39,15 +47,15 @@ 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(n) where n is the length of @store + # Space complexity: O(1) def empty? - raise NotImplementedError, "Method not implemented yet..." + return @store.length == 0 end private @@ -55,17 +63,41 @@ def empty? # 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) where n is the length of the heap + # Space Complexity: 0(logn) def heap_up(index) - + parent_node_index = index.odd? ? (index - 1) / 2 : (index - 2) / 2 + + if @store[index].key >= @store[parent_node_index].key || index == 0 + return + else + swap(index, parent_node_index) + heap_up(parent_node_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 = 2 * index + 1 + right_child = 2 * index + 2 + + if @store[left_child] == nil + return + elsif @store[right_child] == nil && @store[index].key > @store[left_child].key + swap(index, left_child) + return + elsif @store[right_child] == nil + return + else + min_child = @store[right_child].key < @store[left_child].key ? right_child : left_child + + if @store[index].key > @store[min_child].key + swap(index, min_child) + heap_down(min_child) + end + end end # If you want a swap method... you're welcome @@ -74,4 +106,4 @@ def swap(index_1, index_2) @store[index_1] = @store[index_2] @store[index_2] = temp end -end \ No newline at end of file +end diff --git a/test/heapsort_test.rb b/test/heapsort_test.rb index 34402ac..614a799 100644 --- a/test/heapsort_test.rb +++ b/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 + # 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 \ No newline at end of file + end +end diff --git a/test/min_heap_test.rb b/test/min_heap_test.rb index 186d4c2..6b1a05b 100644 --- a/test/min_heap_test.rb +++ b/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 \ No newline at end of file +end