Sometime back, there was a blog on codeforces where people were sharing interesting logic riddles/puzzles/ whatever-you-have-it. I can't find it anymore, either by google search or by Codeforces search. Can anyone provide the link for the same?

P.S I remember there being a problem about getting 2n cards face-down in some order and n guesses, and the solution (which was very cute) was to break the longest permutation into parts smaller than n in size, but I don't remember what it was exactly :(