Solution.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::rc::Rc;
impl Solution {
    pub fn get_minimum_difference(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
        const inf: i32 = 1 << 30;
        let mut ans = inf;
        let mut pre = -inf;

        fn dfs(node: Option<Rc<RefCell<TreeNode>>>, ans: &mut i32, pre: &mut i32) {
            if let Some(n) = node {
                let n = n.borrow();
                dfs(n.left.clone(), ans, pre);
                *ans = (*ans).min(n.val - *pre);
                *pre = n.val;
                dfs(n.right.clone(), ans, pre);
            }
        }

        dfs(root, &mut ans, &mut pre);
        ans
    }
}