Ruby で単方向リスト的な

singly_linked_list.rb

class SinglyLinkedList
  def initialize
    @first_node = nil
  end

  def add(value)
    if last_node = @first_node
      while last_node.next_node
        last_node = last_node.next_node
      end
      last_node.next_node = Node.new(value)
    else
      @first_node = Node.new(value)
    end
    self
  end
  alias_method :<<, :add

  def length
    if node = @first_node
      count = 1
      while node.next_node
        node = node.next_node
        count += 1
      end
      count
    else
      0
    end
  end
  alias_method :size, :length

  def to_s
    inspect
  end

  def inspect
    "<SinglyLinkedList: [#{@first_node ? @first_node.inspect : ''}]>"
  end

  class Node
    attr_reader :value
    attr_accessor :next_node

    def initialize(value)
      @value, @next_node = value, nil
    end

    def to_s
      inspect
    end

    def inspect
      if next_node
        "#{value.inspect}, #{@next_node.inspect}"
      else
        value.inspect
      end
    end
  end
end

if $0 == __FILE__
  p list = SinglyLinkedList.new
  p list.size
  p list << 1
  p list << 'a'
  p list.size
  p list << 2
  p list << 'b'
  p list.size
end

<SinglyLinkedList: []>
0
<SinglyLinkedList: [1]>
<SinglyLinkedList: [1, "a"]>
2
<SinglyLinkedList: [1, "a", 2]>
<SinglyLinkedList: [1, "a", 2, "b"]>
4