class LinkedListNode
  attr_accessor :value, :next_node

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

###### NON-RECURSIVE FUNCTION ######
# 12 -> 37 -> 99 -> nil , original list.
# def reverse_list(list, previous=nil)
#     while list != nil
#         # make list(12) point to nil
#         # make what list is pointing to, point to itself
#         tmp = list.next_node # nil
#         list.next_node = previous # 37 -> 99

#         previous = list # 37
#         list = tmp # nil
#     end
#     previous
# end

def reverse_list(list, previous=nil)

  if list
    og_next_node = list.next_node
    list.next_node = previous
    reverse_list(og_next_node, list)
  end

end

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

node1 = LinkedListNode.new(5)
node2 = LinkedListNode.new(4, node1)
node3 = LinkedListNode.new(3, node2)
node4 = LinkedListNode.new(2, node3)
node5 = LinkedListNode.new(1, node4) # head

print_values(node5)

reverse_list(node5)
print_values(node1)