第5题解法五的下面这两个链接失效:
http://ju.outofmemory.cn/entry/130005
https://articles.leetcode.com/longest-palindromic-substring-part-ii/

我找到了第二个链接的archive: https://web.archive.org/web/20190420104610/http://articles.leetcode.com/longest-palindromic-substring-part-ii/