diff --git a/lib/heap_sort.rb b/lib/heap_sort.rb index c8a32a4..4a1b138 100644 --- a/lib/heap_sort.rb +++ b/lib/heap_sort.rb @@ -1,8 +1,18 @@ +# This method uses a heap to sort an array. +# Time Complexity: O(n log n) - where n is the number of heap nodes in the list +# Space Complexity: O(n) - where n is the length of your list +def heapsort(list) + return list if list.empty? || list.length == 1 + minHeap = MinHeap.new() -# This method uses a heap to sort an array. -# Time Complexity: ? -# Space Complexity: ? -def heap_sort(list) - raise NotImplementedError, "Method not implemented yet..." -end \ No newline at end of file + until list.empty? + minHeap.add(list.pop) + end + + until minHeap.empty? + list << minHeap.remove + end + + return list +end diff --git a/lib/min_heap.rb b/lib/min_heap.rb index 6eaa630..0a1addd 100644 --- a/lib/min_heap.rb +++ b/lib/min_heap.rb @@ -8,27 +8,29 @@ 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(log n) - where n is the number of heap nodes + # Space Complexity: O(1) - constant 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(log n) - where n is the number of heap nodes + # Space Complexity: O(1) - constant def remove() - raise NotImplementedError, "Method not implemented yet..." + swap(0, @store.length - 1) + removed = @store.pop + heap_down(0) + return removed.value end - # Used for Testing def to_s return "[]" if @store.empty? @@ -39,15 +41,15 @@ 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(1) - I assume Ruby is just checking the first index of the array and checking if it's nil or not + # Space complexity: O(1) - constant def empty? - raise NotImplementedError, "Method not implemented yet..." + return @store.empty? end private @@ -55,17 +57,44 @@ 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(log n) - where n is the number of heap nodes + # Space complexity: O(mn) - where m is the space the recursive call is taking up on the stack, and n is the max depth of the tree def heap_up(index) - + parent_index = (index - 1) / 2 + + if @store[parent_index].key > @store[index].key && parent_index >= 0 + swap(parent_index, index) + heap_up(parent_index) + else + return + 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. + # Time complexity: O(log n) - where n is the number of heap nodes + # Space complexity: O(mn) - where m is the space the recursive call is taking up on the stack, and n is the max depth of the tree def heap_down(index) - raise NotImplementedError, "Method not implemented yet..." + left_child_index = index * 2 + 1 + right_child_index = index * 2 + 2 + + if @store[left_child_index].nil? + return + elsif @store[right_child_index].nil? + if @store[left_child_index].key < @store[index].key + swap(index, left_child_index) + end + return + end + + if @store[left_child_index].key < @store[right_child_index].key + swap(index, left_child_index) + heap_down(left_child_index) + else + swap(index, right_child_index) + heap_down(right_child_index) + end end # If you want a swap method... you're welcome @@ -74,4 +103,4 @@ 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..9964e33 100644 --- a/test/heapsort_test.rb +++ b/test/heapsort_test.rb @@ -1,8 +1,8 @@ require_relative "test_helper" -xdescribe "heapsort" do +describe "heapsort" do it "sorts an empty array" do - # Arrange + # Arrange list = [] # Act @@ -13,7 +13,7 @@ end it "can sort a 1-element array" do - # Arrange + # Arrange list = [5] # Act @@ -22,9 +22,9 @@ # Assert expect(result).must_equal [5] end - + it "can sort a 5-element array" do - # Arrange + # Arrange list = [5, 27, 3, 16, -50] # Act @@ -32,5 +32,5 @@ # 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