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Commit dc8654c

Browse files
Add AVL implementation (#4)
* update index on remove * add basic avl implementation * add basic avl tests * export avl useful methods * add traverse method to avl structure * add find method to avl implementation * add capability to update node value in the tree
1 parent f55c828 commit dc8654c

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11 files changed

+292
-2
lines changed

11 files changed

+292
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‎.gitignore‎

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@@ -56,3 +56,4 @@ build-iPhoneSimulator/
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# .rubocop-https?--*
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*.db
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notes/

‎lib/amnesia/memtable.rb‎

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module Amnesia
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class Memtable
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attr_accessor :status
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def initialize
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@store = Amnesia::Support::AVL.new
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@status = :active
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end
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def read(key)
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@store.find(key)
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end
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def write(key, value)
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@store.insert(key, value)
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end
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def flush(segment_handler)
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# TODO: Write a whole block
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@store.traverse { |node| segment_handler.store({ key: node.key, value: node.value }) }
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end
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end
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end

‎lib/amnesia/memtable_handler.rb‎

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module Amnesia
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class MemtableHandler
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def initialize(segment_handler)
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@segment_handler = segment_handler
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@memtables = [Amnesia::Memtable.new]
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end
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def read(key)
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memtable.read(key)
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end
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def write(key, value)
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memtable.write(key, value)
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end
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def flush
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memtable.status = :flushing
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memtable.flush(segment_handler)
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memtable.status = :finished_flusing
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end
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private
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def memtable
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@memtables.first
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end
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end
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end

‎lib/amnesia/segment.rb‎

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@@ -15,8 +15,9 @@ def retrieve(key)
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end
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def remove(key)
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@index_structure.remove(key)
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@storage.delete(key)
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offset = @storage.delete(key)
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@index_structure.add(key, [@storage.size, @storage.size + offset - 1])
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1
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end
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def store(hash_input)

‎lib/amnesia/support/avl.rb‎

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module Amnesia::Support
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class AVL
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attr_reader :root
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def initialize
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@root = nil
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end
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def insert(key, value = nil)
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@root = insert_node(@root, key, value)
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end
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def traverse(&block)
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traverse_node(@root, block)
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end
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def find(key)
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find_node(@root, key)
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end
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private
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def find_node(node, key)
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return node if node.nil? || node.key == key
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return find_node(node.left, key) if key < node.key
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return find_node(node.right, key) if key >= node.key
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end
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def traverse_node(node, block)
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return :noop if node.nil?
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traverse_node(node.left, block)
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block.call({ key: node.key, value: node.value })
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traverse_node(node.right, block)
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end
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def height(node)
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return -1 if node.nil?
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node.height
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end
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def update_node_value(node, value)
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return if node.nil?
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node.value = value
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node
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end
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def insert_node(root, key, value)
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return Node.new(key, value) if root.nil?
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return update_node_value(root, value) if key == root.key
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if key < root.key
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root.left = insert_node(root.left, key, value)
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else
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root.right = insert_node(root.right, key, value)
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end
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update_height(root)
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node_balance_factor = balance_factor(root)
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if node_balance_factor > 1
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root.left = rotate_left(root.left) if key > root.left.key
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return rotate_right(root)
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elsif node_balance_factor < -1
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root.right = rotate_right(root.right) if key < root.right.key
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return rotate_left(root)
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end
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root
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end
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def rotate_right(x)
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a = x.left
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x.left = a.right
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a.right = x
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update_height(x)
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update_height(a)
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a
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end
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def rotate_left(a)
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x = a.right
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a.right = x.left
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x.left = a
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update_height(a)
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update_height(x)
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x
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end
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def update_height(node)
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node.height = [height(node.left), height(node.right)].max + 1
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end
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def balance_factor(node)
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height(node.left) - height(node.right)
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end
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end
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# TODO: This can be a simple Struct
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class Node
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attr_accessor :key, :value, :left, :right, :height
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def initialize(key, value = nil, left = nil, right = nil)
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@key = key
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@value = value
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@left = left
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@right = right
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@height = 0
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end
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end
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end

‎spec/amnesia/memtable_handler_spec.rb‎

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‎spec/amnesia/memtable_spec.rb‎

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‎spec/amnesia/segment_handler_spec.rb‎

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‎spec/amnesia/segment_spec.rb‎

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‎spec/amnesia/support/avl_spec.rb‎

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RSpec.describe Amnesia::Support::AVL do
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subject { described_class.new }
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describe '#insert' do
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context 'when the tree is empty' do
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it 'add the node as the root of the tree' do
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subject.insert(10)
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expect(subject.root.key).to eq(10)
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end
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end
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context 'when the tree already contains nodes' do
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context 'and the insertion makes it unbalanced' do
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it 'adds nodes and balances the tree with single rotations to left' do
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subject.insert(19)
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subject.insert(20)
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subject.insert(21)
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expect(subject.root.key).to eq(20)
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expect(subject.root.left.key).to eq(19)
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expect(subject.root.right.key).to eq(21)
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end
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it 'adds nodes and balances the tree with single rotations to right' do
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subject.insert(21)
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subject.insert(20)
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subject.insert(19)
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expect(subject.root.key).to eq(20)
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expect(subject.root.left.key).to eq(19)
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expect(subject.root.right.key).to eq(21)
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end
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it 'adds nodes and balances the tree with double rotations to left' do
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subject.insert(19)
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subject.insert(25)
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subject.insert(21)
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expect(subject.root.key).to eq(21)
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expect(subject.root.left.key).to eq(19)
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expect(subject.root.right.key).to eq(25)
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end
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it 'adds nodes and balances the tree with double rotations to left' do
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subject.insert(25)
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subject.insert(19)
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subject.insert(21)
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expect(subject.root.key).to eq(21)
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expect(subject.root.left.key).to eq(19)
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expect(subject.root.right.key).to eq(25)
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end
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end
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end
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context 'when the inserted key already exists in the tree' do
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it 'updates the node value' do
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subject.insert(10, 'a')
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subject.insert(11, 'b')
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subject.insert(12, 'c')
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expect(subject.root.key).to eq(11)
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expect(subject.root.right.key).to eq(12)
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expect(subject.root.right.value).to eq('c')
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subject.insert(12, 'd')
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expect(subject.root.key).to eq(11)
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expect(subject.root.right.key).to eq(12)
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expect(subject.root.right.value).to eq('d')
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end
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end
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end
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describe '#traverse' do
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it 'executes the given block for each node' do
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subject.insert(10, 'abc')
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subject.insert(11, 'def')
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subject.insert(12, 'ghi')
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expect do |block|
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subject.traverse(&block)
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end.to yield_successive_args({ key: 10, value: 'abc' }, { key: 11, value: 'def' },
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{ key: 12, value: 'ghi' })
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end
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end
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describe '#find' do
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context 'when the key exists in the tree' do
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it 'returns the found node' do
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subject.insert(10, 'abc')
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found = subject.find(10)
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expect(found.key).to eq(10)
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end
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end
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context 'when the key does not exist in the tree' do
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it 'returns nil' do
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subject.insert(10, 'abc')
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found = subject.find(1)
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expect(found).to be_nil
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end
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end
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end
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end

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