Method min

code/chapter07/bst.rs:149–158

(&self)

    }

    fn min(&self) -> (Option<&T>, Option<&U>) {
        // 最小值一定在最左侧
        match &self.left {
            Some(node) => node.min(),
            None => match &self.key {
                Some(key) => (Some(&key), self.val.as_ref()),
                None => (None, None),
            },
        }
    }

    fn max(&self) -> (Option<&T>, Option<&U>) {
        // 最大值一定在最右侧