singly_linked_list.rb

class SinglyLinkedList

  include Enumerable

  attr_accessor :head

  def initialize(value=nil)
    @head = Node.new(value) if value
  end

  def prepend(value)
    node = Node.new(value)
    node.next = @head
    @head = node
    self
  end

  def last
    node = @head
    while node && node.next
      node = node.next
    end
    node
  end

  def insertAfter(node, new_node)
    new_node.next = node.next
    node.next = new_node
  end

  def append(value)
    last.next = Node.new(value)
  end

  def remove
    node = @head
    @head = node.next
    node
  end

  def length
    tally = 0
    node = @head
    while node.respond_to? :next
      node = node.next
      tally += 1
    end
    tally
  end

  def find(needle)
    node = @head
    until node.nil?
      return node if node.value == needle
      node = node.next
    end
    nil
  end

  def reverse
    reverse_list = SinglyLinkedList.new
    node = @head
    while node
      reverse_list.prepend(node.value)
      node = node.next
    end
    reverse_list
  end

  def reverse!
    @head = reverse.head
    self
  end

  def each
    node = @head
    while node
      yield node.value
      node = node.next
    end
  end

  # def to_s
    #   self.map { |node| node }.join(', ')
  # end

  Node = Struct.new(:value, :next) do
    def to_s
      @value || nil
    end
  end

end