Your task is pretty easy: to write a regular expression that matches [snip] but doesn't match [snip]

Ehm, no. Apparently, we are supposed to read author's mind and come up with some incompletely specified regex.

That's not easy, and it's not good kata design.

Just finished in java, seems to have fixed.

The problem description is confusing: it meant "a single digit".

Use spoiler flag when pasting code like that, rank should be 1, 2, 3, etc.

Try casting to float instead of double. Maybe it'll work.

seems it already has been handled

Feels like that gives away the puzzle part...

Sorry, matrix got messed up on posting, but you get the gist

I'll take suggestions on a concise description if you could provide it

The kata description could stand to be more, well, descriptive. While part of this kata is understanding the puzzle of what the pattern is, it can at least state that clearly.