I'm not using the same language as you do, but I've had issues with the factorial being too big for a number, so my code would only work on smaller strings.
Longer strings would make the factorial too big, and the rest of the code would just fail to work properly.

There is a solution not using factorials.

All test cases are passed but it raises error
-e:5: stack level too deep (SystemStackError). Any suggestions for me ? Thanks in advances

I'm not sure about my recursive solution (I preferred using recursion over while(...))
Can someone explain which is better in that case ? and why ?

Thanks for the kata though :)