NVIDIA Intern interview questions

I had 3 phone interviews and I thought they went pretty good. But, the offer was declined. Not sure what went wrong. I must admit that I did not express too much enthusiasm in their work.

Was referred to the HR by a friend. Got the call in 3 days and set up an interview in a week. I was a little confused since the position was a software intern and I was interviewed by a hardware design engineer! Anyways, he dove straight into the technical questions and didnt waste any time on the typical "Describe yourself".."Strengths, weaknesses" kind of questions. Started off with some OOPs concepts- Polymorphism, Inheritance....examples Then moved onto data structures- Hashtables, Big O of it, How to take care of collusions n stuff! Then he gave a progrmaming problem and was asked to solve it on a collaborative screen sharing software. Kinda fumbled here with a few things, but fixed the bugs as and when he prompted me. He was helpful in that regard. AFter that, he asked some basic DB questions...contraints .. That was it. Lasted for about an hour.