Method insert

publication/code/chapter09/dfs.rs:46–55

(&mut self, data: usize)

    }

    fn insert(&mut self, data: usize) {
        let node = Rc::new(RefCell::new(Node::new(data)));
        if self.is_empty() {
            self.first = Some(node.clone());
            self.last = Some(node);
        } else {
            self.last.as_mut().unwrap().borrow_mut().next = Some(node.clone());
            self.last = Some(node);
        }
    }

    fn print_node(&self) {
        let mut curr = self.first.clone();