I was wondering if a subscribed mentor system is possible. I think it would be very beneficial if once a while we could ask a professional to take a look at our recent codes, and let them advice us on how we can optimize our code or give us specific direction on how to improve our coding skill (like doing these katas or looking at this material).

Hey, i don't know if it's a kata problems or the system problem, but I alreay "submit final" the solution and it still gives me this warning in Solutions:

"Solutions have been withheld

Since you have not yet solved this kata we have hidden the solutions from you. If you choose to view the solutions you will forfeit your eligibility to earn honor/rank progress for this kata."

Yep, i think it's easier to understand now. Thanks.

Is it possible to give an example with n > 10? I am a little bit confuse about the pattern of the number when n > 10.

I think the last test has some problems.

Two word: 'abcde' 'fghi'
Error: 'fghiedcbafghi' should equal 'abcdeihgfabcde'