linked_list.rb

class LinkedList
  def initialize(items)
    items = Array(items)
    if items.size == 1
      @value = items[0]
    else
      @value, @next = items[0], LinkedList.new(items[1..-1])
    end
  end

  def append(value)
    if @next
      @next.add(value)
    else
      @next = LinkedList.new(value)
    end
  end

  def include?(value)
    if @value == value
      true
    elsif @next
      @next.include?(value)
    else
      false
    end
  end

  def each(&blk)
    yield @value
    @next.each(&blk) if @next
  end

  def uniq(new_list = nil)
    new_list ||= LinkedList.new(@value)
    new_list.append(@value) unless new_list.include?(@value)
    @next.uniq(new_list) if @next
    new_list
  end
end