online coding，regrex expression，computer network。some system design。focus on bug free and comnunication skill. very tough question，corner case should be considered. good interviewer they are kind and give me a lot of hint

The process was very simple. Recruiter contacted me on LinkedIn. Finished the online coding assessment. From there a Microsoft Hiring Event day was scheduled. Interview was pretty simple, Straight up leetcode. didn't even change the examples. 1st interview was medium leetcode. When I solved it in 15 mins, 2nd question was asked, After that a behavioral. This interview was finished in under 40 minutes 2nd interviewer asked a very common leetcode question. He asked me if I saw that question on leetcode. when I solved that he asked me to optimize it which I did. And then a behavioral. 3rd interview was OOD after a behavioral question. The interviewer did not ask any follow up questions. This interview was finished in under 40 minutes. 4th interview was a Tree based question which was also solved in the most optimal way. Interviewer mentioned that he has very less experience in java and couldn't understand some of the code. No follow up questions. there was another behavioral question. This interview was also done in 40 minutes. When i checked with recruiter I was told that I was rejected. I was very confident about this interview. I still don't understand why I was rejected.