https://www.luogu.com.cn/discuss/931714 
https://www.luogu.com.cn/fe/api/problem/downloadAttachment/1pm9ddwb 
https://www.bilibili.com/video/BV1rstCeXEzd 
https://www.bilibili.com/video/BV1gYtyeMEJ2 
https://www.bilibili.com/video/BV1KDtUe3EFj 
https://www.noi.cn/xw/2009-08-31/714736.shtml 
注：最后一条与新闻无关。