They focus on the knowledge of algorithm and ability of problem solving. They do not require much background of mobile development, even if the job is about developing apps. Therefore, first there is a online test in which you can choose any language to answer three programming questions. Then, there would be three stages on-site to evaluate interviewee's ability of algorithm and problem solving. In each stage, there would be one employee and he/she would ask 2-3 questions. If you provide one solution to a question, they might ask you how you could improve in time complexity and space complexity. Some questions are quite hard but they would provide some hint and guide you. The overall experience is like discussing and it is likely to learn something in the interview. At the end, HR would introduce about the company and ask some simple questions.