use std::rc::Rc;
use std::cell::RefCell;
use std::collections::VecDeque;

#[derive(Debug, PartialEq, Eq)]
pub struct TreeNode {
    pub val: i32,
    pub left: Option<Rc<RefCell<TreeNode>>>,
    pub right: Option<Rc<RefCell<TreeNode>>>,
}

impl TreeNode {
    #[inline]
    pub fn new(val: i32) -> Self {
        TreeNode { val, left: None, right: None }
    }
}

pub fn build_tree(vals: &[Option<i32>]) -> Option<Rc<RefCell<TreeNode>>> {
    if vals.is_empty() || vals[0].is_none() {
        return None;
    }
    let root = Rc::new(RefCell::new(TreeNode::new(vals[0].unwrap())));
    let mut queue = VecDeque::new();
    queue.push_back(root.clone());
    let mut i = 1;
    while i < vals.len() {
        if let Some(node) = queue.pop_front() {
            if i < vals.len() {
                if let Some(val) = vals[i] {
                    let left = Rc::new(RefCell::new(TreeNode::new(val)));
                    node.borrow_mut().left = Some(left.clone());
                    queue.push_back(left);
                }
                i += 1;
            }
            if i < vals.len() {
                if let Some(val) = vals[i] {
                    let right = Rc::new(RefCell::new(TreeNode::new(val)));
                    node.borrow_mut().right = Some(right.clone());
                    queue.push_back(right);
                }
                i += 1;
            }
        }
    }
    Some(root)
}