冰

参考： http://blog.youkuaiyun.com/ok_again/article/details/16812897 http://blog.youkuaiyun.com/yrleep/article/details/16808827 http://www.cnblogs.com/kuangbin/p/3429062.html （a, b）与 (c, d)的数对个数 转化成 get(b, d)

URAL 1994 The Emperor's plan 求组合数 大数用log #include #include #include #include #include #include #include #include #include #include #include #include #define REP(i, n) for(int i=0; i<n; i++) #define

402E - Strictly Positive Matrix / 403C - Strictly Positive Matrix Let's look at the matrix a as a connectivity matrix of some graph with n vertices. Moreover, if aij > 0, then we have directed

题目：Codeforces Round #258 (Div. 2)Devu and Flowers 题意：n个boxes ，第i个box有fi个flowers，每个boxes中的flowers完全相同，不同boxes的flowers不同，求从n个boxes中取出s个flowers的方案数。n 排列组合的题目，一解法可用容斥原理（inclusion exclusion principle）

求一个数的模p（一般为质数）的逆元，

Codeforces Round #277 (Div. 2) D：