It's a binary search in infinite space. His solution expands the problem area until the number is in the space and then shrinks the problem area until it finds the number. A better solution is to pick an arbitrarily large number and only expand if you have to--otherwise you're shrinking from the very beginning.
That's how I would have answered the question, anyway. But yes, I've dealt with interviewers like this--typically it's because they don't understand the subject matter well enough to evaluate or accept an answer they didn't prepare for.
That's how I would have answered the question, anyway. But yes, I've dealt with interviewers like this--typically it's because they don't understand the subject matter well enough to evaluate or accept an answer they didn't prepare for.