I think the second problem is much more interesting, because the first one can be judged pretty objectively.

The second one is more about trade offs.

Assuming optimal coding, "better" output means more complex code, and means lower performance in terms of processing time and memory usage.

For example, you could write a very complex version that tracked the lifecycle of a file by it's name, and "folded up" the manipulations into a couple of lines of output.

This would be more complex, slower and bug prone - but more human readable.

A test like this is a very interesting way to understand someone's programming taste.