Like you solution very much. It's not universal at all, but for this kata it's very clever.

Yes. You can see it in preconditions in the description:
(x0, y0) - coordinates of the bottom left corner

Cheater ))) Just kidding

Very interesting. But ... Why? If your point was not to use libs - ok. But you used them... I don't get it. By the way, I like complex solutions )

I will not be able to say more precisely.If you will realise it right, you would find solution not so hard. But without seeing your option I can't be more specific. May be only "try to use step debuging" )

Had solve the task for self training with best practices in using comparable interface. Not for smallest solution.

Very interesting solution. Great!

About 2 hours of coding and over 20 lines of code is all it takes to see this. Thanks!!!

Good solution with return format!

But don't throw exception with null and str.length() < 2

I think it's a most elegant solution.

Why casting to long? Test your code with 10000000000000000000.0 or 100000000.5555

Thanks for this kata! Every time when you try to find the correct solution to an interesting mathematical problem, you feel how your brain is working and moving :-D And when you see "Completed in 327ms" - "phew... finally" )