[JoshTriplett]

> If I answered the exact same question by putting the file lines in a data structure and calling Sort() in someone else's interview, I might be thrown out for not giving them the actual algorithm that Sort() implements.

Best of both worlds answer for that kind of question: "In any real program, I'd normally call the standard library implementation, unless there's something wrong with it or profiling suggests that it's a bottleneck. Are you looking for how that library function would be implemented?"

That shows that you know the right real-world answer, but that you're also prepared to explain how that function works as part of the interview. The interviewer could then choose to have you write out the algorithm, or alternatively they could ask questions like "why might the standard implementation be a bottleneck?", which leads in interesting directions as well.