After a first round with HR, second call with an engineering director, then coding interview. I was receiving positive feedback during the implementation, all the code puzzle were solved in O(N), the only not linear was a O(M+N). I did test the code and pseudocode after the interview and it worked. The exercise itself was not that hard. The person interviewed me asked as well random questions on UT, how to, when to. Clearly was following a check list. Not sure how prepared he was on the questions he was asking. I made 4 of 6 steps of the exercise, the guy was interviewing me had to rush 20 mins before the end of the one hour booked for the interview. Not sure lf it was a strategy to get rid of me :), I'm confident I was going to complete the test. It's fine to do not pass an interview, for any reason.. when I asked HR for a feedback I did not receive any reply with evidence unfortunately. Interviews are way to learn as well. I do interview people frequently, the approach is different.