[yongjik]

Another equally plausible hypothesis is that the other 4 interviewers gave only lukewarm feedback ("This person seems to know his/her stuff, but I'm somewhat reserved because...") and the decision ultimately against you.

Yet another hypothesis (not pleasant to consider, but it happens) is that it's got nothing to do with linked list and everything to do with another interviewer who gave you a "warm-up question", saw you spend 30 minutes on it, decided it's a lost cause and just made sure you feel good about the result (because that's the professional thing to do, and you never know if the candidate might pull off something spectacular with the next interviewer).

In general, what a candidate feels about an interview has very little correlation with how the interviewer scores the candidate. (Even for a single fixed candidate.)

[helpless]

other interview was finished 15 minutes early with 2 problem solved.