I rather spend my time with a useful solution than this path. Also it's a BS question anyway.

Well in the case of Google's interviewing techniques they don't really care about the question per se, what they look for is how folks reason about things. You can start down one path, back up, head down another, and explore a variety of paths to possible solutions. The only bad answer is "That's a silly question, why would I ever need to do that?" or something similar. An unwillingness to engage in a discussion, even about 'impossible' problems, was the most common reason I saw on feedback where Google passed on the candidate.

> Well in the case of Google's interviewing techniques they don't really care about the question per se

From my experience interviewing for Google, I beg to differ. Many other accounts seem to confirm this.