Google

Google contacted me; they had my resume from an old interview many years ago. After a few email exchanges about available positions, a phone screen was arranged. During the phone screen, they asked technical questions to gauge my skills. It looks

Screen phone interview. Talked about skills, background, and what I wanted to get out of it. It was normal, and I didn't get very far. I also asked some questions related to the work.

Come in, dig over the CV, and go straight up to the board. Start solving the question in whichever programming language you want. You'll need to explain about computing speed, memory requirements, tradeoffs, etc.