class LinkedListNode
    attr_accessor :value, :next_node

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

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

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

print_values(node3)
reverse_list(node3)
print_values(node1)