Method contains

publication/code/chapter10/lru.rs:112–114

(&mut self, key: &K)

    }

    fn contains(&mut self, key: &K) -> bool {
        self.map.contains_key(key)
    }

    // 获取某个 key 的值，移除原来位置的值并在头部加入
    fn access(&mut self, key: &K) {