Thx for the post, still, the first thing I would focus on in the interview is what the candidate has done before and I would bet on that. Even if he/she is a student, and all you're looking on is student portfolio

"Tech interviews should center on algorithmic complexity, abstraction and isolation, and how the stuff you learn in CS101 actually applies in the real world"

I am not in any way connected with this startup but the nice way to check the above would be to use codility http://codility.com/