Note 题单: https://www.luogu.com.cn/training/424544#problems 黄 8183 Done 3662 done 真题单: https://www.luogu.com.cn/problem/list?keyword=%5BUSACO%5D%20S&type=AT%7CB%7CCF%7CP%7CSP%7CUVA&difficulty=3&page=1