There is no sample test, only one main test, because it only one time in Japan now. What else would you like to tested?

No problem, cheers.

Not a kata issue. Use Question label next time.

You forgot 5.

Hi @ThomasBucaioni also note that almost 5,000 coders have solved the C++ version, so the chances of such an extant bug is highly unlikely.

I think that's a problem on how you calculate len.

the output says "e10 is not a valid position..." But e10 is in the solution

"Is not a valid position" means that it's wrong and shouldn't be there.

Columns are marked with letters a-j, and rows with single digit from 1 to 0 (first row is marked with 1, ninth row is marked with 9, and tenth row is marked with 0)

Row #10 should have an index of 0 instead of 10, not an issue.

Are you completely sure your output string does not contain any stray comma?

You're returning a string with a comma at the end, and you know it considering you slice the last character away when printing the result. Not an issue.

Are you completely sure your output string is formatted correctly and does not contain any stray comma or other characters?

If so, could you share your code? (remember about code formatting and spoiler flag)

Then you most probably have a bug.

I am going to close the original issue as resolved, and if you think there's a bug in the kata, crete a new, dedicated issue with some details which will help to track the problem down.

Please reset your trainer (remember to back up your solution!), refresh the page, and check again.

35 characters min, here too... Walrus didn't helped too much... :)

indent can be 1 space too. but for this to works, you need one line!

Yes.