An HR contacted me and said I should complete one of their three hardest puzzles. The puzzle was interesting, but the fact that I spent 2.5 days to do that (1 day was spent on submitting it in a correct way so that the puzzle robot accepts it), and it won't help when interviewing anywhere else, annoyed me. I then had a phone interview. The guy was very clever, which was nice. The questions were: what is the most exciting project you had, and white a function to multiply two arbitrarily large integers. I spent quite a while writing a recursive solution for the problem, made some mistakes during that, but fixed those purely by myself. The interviewer did not provide any feedback during the process when I described my "way of thinking" and the programming, so I even had to ask whether he was on the line. With phone interview, not feedback is a bit too harsh, imho. Then I was asked to write an iterative solution, and I completed it as well. I did not write the solutions easily, and my way of explaining was not perfectly clear and great, but I solved what I was asked. Then the HR contacted me saying they won't consider me anymore this year. I politely asked for feedback, but got the answer that there is nothing to share. Quite surprising for a social-oriented company.