class LinkedListNode
  attr_accessor :value, :next_node

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

  def reverse_list(list, previous = nil)
    while list
      old_next = list.next_node
      list.next_node = previous
      previous = list
      list = old_next
    end
    previous
  end

  def print_values(list_node)
    if list_node
      print "#{list_node.value} --> "
      print_values(list_node.next_node)
    else
      print "nil\n"
    end
  end
end

node1 = LinkedListNode.new(37)
node2 = LinkedListNode.new(99, node1)
node3 = LinkedListNode.new(12, node2)

revlist = node3.reverse_list(node3)
node3.print_values(revlist)