Two sections of on demand interview. The first part has 7 questions, including some behavior questions and algorithm description (branch-and-bound). The second part is a multiple choices section, which has 25 (!) questions, you only have 1-3 minutes to answer each of them. Questions including computation, complexity and general theories of linear and mixed-integer programming. I did not expect there are so many multiple choices and we only have very limit of time to answer each, so I did not answer it well.