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

// Definition for a binary tree node.
// #[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,
//         }
//     }
// }

// struct Solution {}
impl Solution {
    pub fn find_mode(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
        let mut counters: BTreeMap<i32, usize> = BTreeMap::new();

        let mut stack: Vec<Option<Rc<RefCell<TreeNode>>>> = Vec::new();
        stack.push(root.clone());

        while let Some(node) = stack.pop() {
            if node.is_none() {
                continue;
            }

            let node = node.unwrap();
            let n = node.borrow();

            counters
                .entry(n.val)
                .and_modify(|curr| *curr += 1)
                .or_insert(1);
            stack.push(n.left.clone());
            stack.push(n.right.clone());
        }

        let maximum = *counters.values().max().unwrap();
        counters
            .iter()
            .filter_map(|(&k, &c)| if c == maximum { Some(k) } else { None })
            .collect()
    }
}