diff --git a/lib/heap_sort.rb b/lib/heap_sort.rb index 6b692e4..e0dcd56 100644 --- a/lib/heap_sort.rb +++ b/lib/heap_sort.rb @@ -1,8 +1,16 @@ - - # This method uses a heap to sort an array. -# Time Complexity: ? -# Space Complexity: ? +# Time Complexity: O(n log n) +# Space Complexity: O(n) def heapsort(list) - raise NotImplementedError, "Method not implemented yet..." + heap = MinHeap.new + + list.each do |element| + heap.add(element) + end + + list.each_with_index do |number, index| + list[index] = heap.remove() + end + + return list end \ No newline at end of file diff --git a/lib/min_heap.rb b/lib/min_heap.rb index 6eaa630..7e0568e 100644 --- a/lib/min_heap.rb +++ b/lib/min_heap.rb @@ -14,20 +14,27 @@ def initialize end # This method adds a HeapNode instance to the heap - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(log n) + # 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(log n) + # Space Complexity: O(log n) def remove() - raise NotImplementedError, "Method not implemented yet..." - end + return nil if @store.empty? + + swap(0, @store.length - 1) + removed = @store.pop + + heap_down(0) unless @store.empty? + return removed.value + end # Used for Testing def to_s @@ -44,10 +51,10 @@ def to_s 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 @store.length == 0 ? true : false end private @@ -55,20 +62,46 @@ 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) + # Space complexity: O(log n) def heap_up(index) - + return if index == 0 + parent = (index - 1) / 2 + + if @store[index].key < @store[parent].key + swap(index, parent) + heap_up(parent) + 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..." + right_side = 2 * index + 2 + left_side = 2 * index + 1 + + if right_side < @store.length + if @store[left_side].key > @store[right_side].key + smaller = right_side + else + smaller = left_side + end + + if @store[index].key > @store[smaller].key + swap(index, smaller) + heap_down(smaller) + end + + elsif left_side < @store.length + if @store[index].key > @store[left_side].key + swap(index, left_side) + end + end end - # If you want a swap method... you're welcome + # If you want a swap method... you're welcome THANK YOU CHRIS :) def swap(index_1, index_2) temp = @store[index_1] @store[index_1] = @store[index_2] diff --git a/test/heapsort_test.rb b/test/heapsort_test.rb index 34402ac..7ce79b7 100644 --- a/test/heapsort_test.rb +++ b/test/heapsort_test.rb @@ -1,6 +1,6 @@ require_relative "test_helper" -xdescribe "heapsort" do +describe "heapsort" do it "sorts an empty array" do # Arrange list = []