It was very nice experience to be an interviewer. I helped the interviewer learn a brute force solution first and then we had very good discussion on the optimal solution using dynamic programming. The peer is preparing Google phone screen, I may come cross a Google future employee this time. I met a senior undergraduate student who also works full time for a startup company in silicon valley area.
Of course I could not tell from the person how good she will be, specially when a peer is undergraduate student. But it is very easy to communicate with the peer.
I also learned from the peer. I challenged her code using comment line 63, I told her that line 68, temp_max *= arr[i] * arr[j], and then she added a few lines of comments from line 64 to 67, and then I understood her idea to use dynamic programming. She fixed the bug, and line 68: temp_max *= arr[j], arr[i] is removed from the product.