摘要：
非常妙的经典模型转化啊…… You're given a matrix A of size n × n. Let's call the matrix with nonnegative elements magic if it is symmetric (so aij = aji), aii = 0 阅读全文
摘要：
比较套路的组合数学题 For a sequence a of n integers between 1 and m, inclusive, denote f(a) as the number of distinct subsequences of a (including the empty sub 阅读全文