Microsoft Software Developer interview questions

Was asked multiple question about improving the complexity of one question. The interviewer only gave me positive feedback and I asked him if the answer I gave him made sense to him, to which he answered "yes". Still I got a rejection email saying "I'm not a good fit". Discussed it with some friends and it made sense to them also but I don't what else the interviewer was looking for in a candidate.

I'm a computer science student. The interview I did was over Skype for Business. The interview was about 30 minutes. The interviewer was very nice and allowed me to steer the conversation in whichever topic I wanted. After talking about myself I was given a programming challenge. Unfortunately it seems nerves got to me too much. At the end I was able to ask any questions that I wanted. Overall it was a good experience.