✨ Add ruby BST

README.md

@@ -1776,8 +1776,8 @@ In order to achieve greater coverage and encourage more people to contribute to
  </a>
  </td>
  <td> <!-- Ruby -->
- <a href="./CONTRIBUTING.md">
- <img align="center" height="25" src="./logos/github.svg" />
+ <a href="./src/ruby/binary_search_tree.rb">
+ <img align="center" height="25" src="./logos/ruby.svg" />
  </a>
  </td>
  <td> <!-- JavaScript -->

src/ruby/binary_search_tree.rb

@@ -0,0 +1,213 @@
+class BinarySearchTree
+ class Node
+ attr_accessor :left, :right, :value
+
+ def initialize(value)
+ @left = nil
+ @right = nil
+ @value = value
+ end
+ end
+
+ def initialize
+ @root = nil
+ end
+
+ attr_reader :root
+
+ def insert(value)
+ new_node = Node.new(value)
+
+ if @root.nil?
+ @root = new_node
+ return self
+ end
+
+ current_node = @root
+
+ loop do
+ if value < current_node.value
+ if current_node.left.nil?
+ current_node.left = new_node
+ return self
+ end
+ current_node = current_node.left
+ else
+ if current_node.right.nil?
+ current_node.right = new_node
+ return self
+ end
+ current_node = current_node.right
+ end
+ end
+
+ self
+ end
+
+ def lookup(value)
+ return nil if @root.nil?
+
+ current_node = @root
+
+ until current_node.nil?
+ if value < current_node.value
+ current_node = current_node.left
+ elsif value > current_node.value
+ current_node = current_node.right
+ else
+ return current_node
+ end
+ end
+
+ nil
+ end
+
+ def remove(value)
+ return false if @root.nil?
+
+ current_node = @root
+ parent_node = nil
+
+ while current_node
+ if value < current_node.value
+ parent_node = current_node
+ current_node = current_node.left
+ elsif value > current_node.value
+ parent_node = current_node
+ current_node = current_node.right
+ elsif current_node.value == value
+ # We have a match, get to work!
+
+ if current_node.right.nil?
+ update_parent_link(parent_node, current_node, current_node.left)
+ elsif current_node.right.left.nil?
+ current_node.right.left = current_node.left
+ update_parent_link(parent_node, current_node, current_node.right)
+ else
+ leftmost, leftmost_parent = find_leftmost(current_node.right)
+ leftmost_parent.left = leftmost.right
+ leftmost.left = current_node.left
+ leftmost.right = current_node.right
+ update_parent_link(parent_node, current_node, leftmost)
+ end
+
+ return true
+ end
+ end
+
+ false
+ end
+
+ def traverse(node = @root)
+ return nil if node.nil?
+
+ tree = { value: node.value }
+ tree[:left] = traverse(node.left)
+ tree[:right] = traverse(node.right)
+
+ tree
+ end
+
+ private
+
+ def update_parent_link(parent_node, current_node, new_node)
+ if parent_node.nil?
+ @root = new_node
+ elsif current_node.value < parent_node.value
+ parent_node.left = new_node
+ else
+ parent_node.right = new_node
+ end
+ end
+
+ def find_leftmost(node)
+ leftmost = node.left
+ leftmost_parent = node
+
+ while leftmost.left
+ leftmost_parent = leftmost
+ leftmost = leftmost.left
+ end
+
+ [leftmost, leftmost_parent]
+ end
+end
+
+RSpec.describe BinarySearchTree do
+ let(:bst) { BinarySearchTree.new }
+
+ before(:each) do
+ # Construct the following tree:
+ #
+ # 9
+ # 4 20
+ # 1 6 15 170
+ #
+ bst.insert(9)
+ bst.insert(4)
+ bst.insert(6)
+ bst.insert(20)
+ bst.insert(170)
+ bst.insert(15)
+ bst.insert(1)
+ end
+
+ describe '#insert' do
+ it 'adds a value to the tree' do
+ expect(bst.traverse).to eq({ value: 9,
+ left: { value: 4,
+ left: { value: 1, left: nil, right: nil },
+ right: { value: 6, left: nil, right: nil } },
+ right: { value: 20, left: { value: 15, left: nil, right: nil },
+ right: { value: 170, left: nil, right: nil } } })
+ end
+ end
+
+ describe '#lookup' do
+ it 'finds a value in the tree' do
+ node = bst.lookup(15)
+ expect(node.value).to eq(15)
+ end
+
+ it 'returns nil for a value not in the tree' do
+ node = bst.lookup(100)
+ expect(node).to be_nil
+ end
+ end
+
+ describe '#remove' do
+ it 'removes a leaf node' do
+ expect(bst.remove(1)).to be true
+
+ expect(bst.traverse).to eq({ value: 9,
+ left: { value: 4, left: nil,
+ right: { value: 6, left: nil, right: nil } },
+ right: { value: 20, left: { value: 15, left: nil, right: nil },
+ right: { value: 170, left: nil, right: nil } } })
+ end
+
+ it 'removes a node with one child' do
+ expect(bst.remove(20)).to be true
+
+ expect(bst.traverse).to eq({ value: 9,
+ left: { value: 4, left: { value: 1, left: nil, right: nil },
+ right: { value: 6, left: nil, right: nil } },
+ right: { value: 170, left: { value: 15, left: nil, right: nil },
+ right: nil } })
+ end
+
+ it 'removes a node with two children' do
+ expect(bst.remove(4)).to be true
+
+ expect(bst.traverse).to eq({ value: 9,
+ left: { value: 6, left: { value: 1, left: nil, right: nil },
+ right: nil },
+ right: { value: 20, left: { value: 15, left: nil, right: nil },
+ right: { value: 170, left: nil, right: nil } } })
+ end
+
+ it 'returns false for a value not in the tree' do
+ expect(bst.remove(100)).to be false
+ end
+ end
+end