Microsoft Interview Experience (part 1)

I just finished my 2nd round of interview with microsoft.

I began my journey with microsoft when I submitted my resume through microsoft career website during July (if I remembered correctly). Then randomly on September, after I forgot that I had sent resume to microsoft, I got an email invitation to interview. The interview would take place in my uni career center. There would be 2 interviews, each interview took about 30 mins.

On the interview day, the first person I interviewed with is HR person. She asked me about my project and some other typical questions that HR usually asked but more techie than behaviour. Like, she asked me how would I explain what internet is to my grandparents. I thought I did well in this interview.

The second interviewer is technical stuff only. After he introduced himself that he was in SQL team, we went straight to the question. The question is "Find the average of the numbers. You don't know how many numbers the user would input. Ignore all duplicate numbers"
The question wasn't that hard when I thought about it after the interview. But during that time, I was nervous and my brain was still not working properly. Anyway, I answered that I would use hash table to check for a duplicate. And he asked me to talk about time complexity of my program. At the end, he also asked are there any other way to solve this problem. I answered him I would use BST. Thinking back, I should have answered with BST instead of hash table, because I would need to reserved a lot of spaces for hash table and BST seems more appropriate in this question.

Anyway, I felt that I did horribly in technical interview. I did very little preparation the day before the interview and I didn't brush up my data structure and algorithm knowledge.
I wouldn't be surprise if I fail. To tell you the truth, I went to the interview with no expectation to myself. I just thought that it would be a good experience for me before I graduate and need to hunt for a job.

Anyway, after a week or so, I got email from recruiter that I will continue for the 2nd round of interview.