In yesterday's div1+2 contest problem E (1804E) required an optimization for bitmask dp looking for cycles that has appeared waaaaaay before in cf, dating back to the beta days in this problem. It seems that it wasn't that well known, looking at the number of TLE submissions, so I'm posting this blog to remind people that there are old rounds/contests and they do have some good or educational problems.

One silly lesson that I learned from an old-ish problem is that writing some combinatorics problems in polynomial form sometimes might expose some observations that might not be obvious at first glance. Perhaps if you have some similar experience you could share it in this blog, as there would be at least one person interested in seeing it (me).