is_valid_bst.rs

#[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::rc::Rc;
struct Solution;
impl Solution {
    pub fn is_valid_bst(root: Option<Rc<RefCell<TreeNode>>>) -> bool {
        fn check(root: &Option<Rc<RefCell<TreeNode>>>) -> (i32, bool, i32) {
            let val = root.clone().unwrap().borrow().val;
            let left = root.clone().unwrap().borrow().left.clone();
            let right = root.clone().unwrap().borrow().right.clone();

            if left.is_some() && right.is_some() {
                let (lmn, lans, lmx) = check(&left);
                let (rmn, rans, rmx) = check(&right);
                if lmx<val && rmn>val {
                    return (lmn.min(rmn), true, lmx.min(rmx));
                } else {
                    return (lmn.min(rmn), false, lmx.min(rmx));
                }
            }
            (val, true, val)
        }
        check(&root).1
    }
}

fn main() {}