I agree with the other comments. No strings, no complicated math. Clean and simple.

Best solution!

It's really cool!!!

This solution really should be upvoted, it is perfect, simple, and has a very fast execution time!

Thanks , missed that

char is already a number in Java, don't need to convert to int !

Very not efficient solution, we use String: that create useless objects, use memory and cpu for nothing.

The best solution is the arithmic one, very more efficient.