Find leaves of binary tree

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

impl Solution {
  pub fn find_leaves(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<Vec<i32>> {
    let mut result = Vec::new();

    fn height(node: &Option<Rc<RefCell<TreeNode>>>, result: &mut Vec<Vec<i32>>) -> i32 {
      match node {
        None => -1,
        Some(n) => {
          let n = n.borrow();
          let h = 1 + height(&n.left, result).max(height(&n.right, result));
          if h as usize >= result.len() {
            result.resize(h as usize + 1, Vec::new());
          }
          result[h as usize].push(n.val);
          h
        }
      }
    }

    height(&root, &mut result);
    result
  }
}