摘要： problem linkhttp://codeforces.com/contest/118/problem/D2011-10-921:38 It seems this problem is about enumeration of combination.21:42 Using DP.21:44 If I had already get F(n-1), means in total n-1 units, there are F(n-1) kinds of beautiful arrangements. suppose the beautiful arrangement is xxxxxx... 阅读全文