Given a string Str, rearrange Str such that the resultant string T maximizes min (LCS(Str, T) and LCS(Str, reverse(T))).

The ratio of registered candidates and those making at least one submission is bad. Only 9249 out of 21518 will be rated; this leads to either a very small increase in the rating of players rated below 1400. I think it's because of the increasing difficulty of 1st questions in the contest(which is a good thing, I think), so if the system rated everybody who registered, it would be much fairer for those who actually submitted; some OJs do this already.

Codeforces Round #853 (Div. 2) out of 24262, 7432 candidates will be rated.

Educational Codeforces Round 143 (Rated for Div. 2) out of 27849, 13755 candidates will be rated.

Codeforces Round #852 (Div. 2) out of 25361, 9339 candidates will be rated.

These are the stats of the last 4 rated contests; 1st one is in the paragraph, do comment on your thoughts about this.