LeetCode 549. Binary Tree Longest Consecutive Sequence II

Problem Statement

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

impl Solution {
    fn dfs(root: Option<Rc<RefCell<TreeNode>>>,
           parent: Option<Rc<RefCell<TreeNode>>>, ans: &mut i32) -> (i32, i32) {
        if let Some(node) = root {
            let (mut incr, mut decr) = (0, 0);
            let l = Self::dfs(node.borrow().left.clone(), Some(node.clone()), ans);
            let r = Self::dfs(node.borrow().right.clone(), Some(node.clone()), ans);
            *ans = std::cmp::max(*ans, std::cmp::max(l.0 + r.1 + 1, l.1 + r.0 + 1));
            let p = parent.unwrap();
            if node.borrow().val == p.borrow().val + 1 {
                incr = std::cmp::max(l.0, r.0) + 1;
            }
            if node.borrow().val + 1 == p.borrow().val {
                decr = std::cmp::max(l.1, r.1) + 1;
            }
            return (incr, decr);
        } else {
            return (0, 0);
        }
    }

    pub fn longest_consecutive(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
        let mut ans = 0;
        Self::dfs(root.clone(), root.clone(), &mut ans);
        return ans;
    }
}