https://max-cheng.github.io/posts/2019/03/2019leetcode%E6%98%A5%E5%AD%A3%E5%85%A8%E5%9B%BD%E9%AB%98%E6%A0%A1%E8%B5%9B%E5%86%B3%E8%B5%9B-1.-%E6%9C%89%E5%BA%8F%E6%95%B0%E7%BB%84%E4%B8%AD%E7%9A%84%E7%BC%BA%E5%A4%B1%E5%85%83%E7%B4%A0/