I think I know why so many of these are simple binary search questions. If you actually read the full interview descriptions that most of these come from, you'll see that the vast majority of them were rejected. As an interviewer, the very first question I ask is "what is a binary search and what is its big-O run time?" Assuming the candidate has a CS background, this is meant to take up about 15 seconds of the interview and allow us to get to the real questions. I suspect many other interviewers do something similar. Most of these posters likely struggled with it and didn't get to the real questions, so that's all they could share.