Amazon Software Developer interview questions

Had four telephonic round, most of the questions were on algorithms and some question on c++ basics. Every round went well but the interviewer was expecting answers in the perspective of Java and object oriented. I am a c developer. so dint got selected

The first around phone interview was easy and it was question about binary tree. The second around was relatively harder. The interviewer asked a system design problem. I didn't prepare for that kind of questions.