One interview by phone. I thought I've answered all of the questions correctly but did not pass to next phase. Asked about matrix, memory optimization, complexity... He asked a lot of questions and in the end, I had to write an algorithm. He hanged up the call and gave me 10 minutes to solve the problem. I could do it in less time and he called me and asked to explain my algorithm. Since it was an international call, I was not listening the interviewer very well too, but he was incredibly calm and repeated everything patiently.