Microsoft Software Engineer interview questions

On campus interview with a GPU expert, 30 minutes. First he asked me why are you interested in Microsoft. Then ask a very simple technical question followed by a strange algorithm I've never seen before.

Flew out to Microsoft's office in Pittsburgh, PA. The process was standard. 4 interviews with different people. Answered all of the questions with little help. Asked clarifying questions, explained my thought process, and expressed passion and the willingness to grow. Rejected shortly after I arrived home with no feedback on what I did wrong. They receive so many applications that I doubt they really care.