Totally waste of time. I already faced the same issue last year. HR won't share any details about interview like what would be the round. Interviewer was not ready for listening my answer. I was sharing perfect solution which could take o(logn) , but he wants to implement using inbuilt function and they didn't share what that function is.. there are number of issues during this round. They won't ask the question what you have worked on. It will be based on what they know.