Solution2.rs

// 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
//     }
//   }
// }
use std::cell::RefCell;
use std::collections::VecDeque;
use std::rc::Rc;
impl Solution {
    fn dfs(root: &Option<Rc<RefCell<TreeNode>>>, cur: i32, max: &mut i32, res: &mut i32) {
        if root.is_none() {
            return;
        }
        let root = root.as_ref().unwrap().borrow();
        Self::dfs(&root.left, cur + 1, max, res);
        Self::dfs(&root.right, cur + 1, max, res);
        if *max < cur {
            *max = cur;
            *res = root.val;
        }
    }

    pub fn find_bottom_left_value(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
        let mut max = 0;
        let mut res = 0;
        Self::dfs(&root, 1, &mut max, &mut res);
        res
    }
}