Method rotate_right

publication/code/chapter08/avl.rs:205–212

(&mut self)

    }

    fn rotate_right(&mut self) {
        let mut n = replace(self, Null);
        let mut left = replace(n.left_subtree(), Null);
        let left_right = replace(left.right_subtree(), Null);
        *n.left_subtree() = left_right;
        *left.right_subtree() = n;
        *self = left;
    }

    // 插入节点
    fn insert(&mut self, key: T) -> (bool, bool) {