From aec5d45e46d1efdd7fb2844e980447c7584f727c Mon Sep 17 00:00:00 2001 From: Erica Norris Date: Mon, 30 Sep 2019 21:07:49 -0700 Subject: [PATCH 1/3] implemented min_heap methods --- lib/min_heap.rb | 41 ++++++++++++++++++++++++++++++++++++----- 1 file changed, 36 insertions(+), 5 deletions(-) diff --git a/lib/min_heap.rb b/lib/min_heap.rb index 6eaa630..282a4b5 100644 --- a/lib/min_heap.rb +++ b/lib/min_heap.rb @@ -17,7 +17,14 @@ def initialize # Time Complexity: ? # Space Complexity: ? def add(key, value = key) - raise NotImplementedError, "Method not implemented yet..." + node = HeapNode.new(key, value) + + if @store.empty? + @store.push(node) + else + @store.push(node) + heap_up(@store.length - 1) + end end # This method removes and returns an element from the heap @@ -25,7 +32,12 @@ def add(key, value = key) # Time Complexity: ? # Space Complexity: ? def remove() - raise NotImplementedError, "Method not implemented yet..." + return nil if @store.empty? + + swap(0, @store.length - 1) + removed = @store.pop + heap_down(0) + return removed.value end @@ -47,7 +59,7 @@ def to_s # Time complexity: ? # Space complexity: ? def empty? - raise NotImplementedError, "Method not implemented yet..." + return @store.length == 0 end private @@ -58,14 +70,33 @@ def empty? # Time complexity: ? # Space complexity: ? def heap_up(index) - + return if @store[index].nil? || index == 0 + + parent_index = (index - 1) / 2 + + if @store[parent_index].key > @store[index].key + swap(index, parent_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..." + left = (index * 2) + 1 + right = (index * 2) + 2 + + if !@store[left] && !@store[right] + return + elsif !@store[right] + min = left + else + min = @store[left].key <= @store[right].key ? left : right + end + + swap(index, min) + heap_down(min) end # If you want a swap method... you're welcome From 8ab3a201de47a086521815b6944bd748035bcf48 Mon Sep 17 00:00:00 2001 From: Erica Norris Date: Mon, 30 Sep 2019 21:41:01 -0700 Subject: [PATCH 2/3] unskipped test, implemented heapsort, updated heap_down for heap_sort to work properly --- lib/heap_sort.rb | 18 ++++++++++++++---- lib/min_heap.rb | 9 ++++++--- test/heapsort_test.rb | 2 +- 3 files changed, 21 insertions(+), 8 deletions(-) diff --git a/lib/heap_sort.rb b/lib/heap_sort.rb index c8a32a4..60a290b 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: ? # Space Complexity: ? -def heap_sort(list) - raise NotImplementedError, "Method not implemented yet..." +def heapsort(list) + return list if list.length < 2 + + heap = MinHeap.new + + until list.empty? + heap.add(list.pop) + end + + until heap.empty? + list.push(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 282a4b5..9d59266 100644 --- a/lib/min_heap.rb +++ b/lib/min_heap.rb @@ -87,12 +87,15 @@ def heap_down(index) left = (index * 2) + 1 right = (index * 2) + 2 - if !@store[left] && !@store[right] - return + return if @store[left].nil? + + if !@store[right] + swap(index, left) if @store[index].value > @store[left].value + return elsif !@store[right] min = left else - min = @store[left].key <= @store[right].key ? left : right + min = @store[left].key < @store[right].key ? left : right end swap(index, min) 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 = [] From c8153f840a45d4c4ef6b840afb6d22c29e0b629f Mon Sep 17 00:00:00 2001 From: Erica Norris Date: Wed, 2 Oct 2019 09:16:36 -0700 Subject: [PATCH 3/3] added time and space complexities --- lib/heap_sort.rb | 4 ++-- lib/min_heap.rb | 20 +++++++++++--------- 2 files changed, 13 insertions(+), 11 deletions(-) diff --git a/lib/heap_sort.rb b/lib/heap_sort.rb index 60a290b..8b094b6 100644 --- a/lib/heap_sort.rb +++ b/lib/heap_sort.rb @@ -1,6 +1,6 @@ # This method uses a heap to sort an array. -# Time Complexity: ? -# Space Complexity: ? +# Time Complexity: O(n log n) where n is the number of items in the list +# Space Complexity: O(n) where n is the number of items in the list def heapsort(list) return list if list.length < 2 diff --git a/lib/min_heap.rb b/lib/min_heap.rb index 9d59266..c27ff6b 100644 --- a/lib/min_heap.rb +++ b/lib/min_heap.rb @@ -14,8 +14,8 @@ def initialize 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 items in the heap + # Space Complexity: O(1) def add(key, value = key) node = HeapNode.new(key, value) @@ -29,8 +29,8 @@ def add(key, value = key) # 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 items in the heap + # Space Complexity: O(1) def remove() return nil if @store.empty? @@ -56,8 +56,11 @@ def to_s end # This method returns true if the heap is empty - # Time complexity: ? - # Space complexity: ? + # Time complexity: O(n) where n is the number of items in the heap-- + # although I feel like this could be made to be O(1) + # because we don't need to actually calcuate the length of @store, + # we only need to check whether it has at least one item + # Space complexity: O(1) def empty? return @store.length == 0 end @@ -66,9 +69,8 @@ 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 items in the heap + # Space complexity: O(1) def heap_up(index) return if @store[index].nil? || index == 0