use std::cell::RefCell;
use std::rc::{Rc, Weak};
 
#[derive(Debug)]
struct Node {
    value: i32,
    children: RefCell<Vec<Rc<Node>>>,
    parent: RefCell<Weak<Node>>,
}
 
impl Node {
    fn new(value: i32) -> Rc<Self> {
        Rc::new(Node {
            value,
            children: RefCell::new(Vec::new()),
            parent: RefCell::new(Weak::new()),
        })
    }
 
    fn add_child(&self, child: Rc<Node>) {
        self.children.borrow_mut().push(Rc::clone(&child));
        *child.parent.borrow_mut() = Rc::downgrade(self);
    }
 
    fn get_parent(&self) -> Option<Rc<Node>> {
        self.parent.borrow().upgrade()
    }
}
 
fn main() {
    let leaf = Node::new(3);
    let branch = Node::new(5);
    branch.add_child(Rc::clone(&leaf));
 
    println!("Leaf parent: {:?}", leaf.get_parent());
    println!("Branch strong count: {}", Rc::strong_count(&branch));
    println!("Leaf strong count: {}", Rc::strong_count(&leaf));
}