摘要：
C. Did We Get Everything Covered? You are given two integers $n$ and $k$ along with a string $s$. Your task is to check whether all possible strings o 阅读全文
摘要：
D. Good Trip There are $n$ children in a class, $m$ pairs among them are friends. The $i$-th pair who are friends have a friendship value of $f_i$. Th 阅读全文