NVIDIA interview questions

Two rounds phone interview. The first time is the manager, then second round is a PhD in the team. They are very nice and we go through my resume and asked the questions related to it. It happens one year ago, I really cannot remember too much detail.

HR really pissed me off by taking more than week time between each phone screen. totally I had 3 phone screens and 6 on-site 1:1 interviews. In almost 3 interviews I faced same question of reversing a linked list. I can say only one round was challenging where I was asked to solve a puzzle using Divide and Conq. method. All my Interviews went really good but I got reject saying no direct/relevant experience.