It is an old Kata, that's why it's 6 Kyu.

This is maybe a 7kyu riddle ?

Language?

Also, please post the test case and your result so I can check.

Thanks for helping.

Strange behaviour, I copied all test values which I printed as you suggested and try locally, all seems good. But when I try running it here with same code, it says -Error: arrays first differed at element [##]; expected: #### but was: []####

Try printing the input array to see the test case.

Error: arrays first differed at element [17]; expected:<[b]wnryvzvogpwq> but was:<[]wnryvzvogpwq>
what could be the test values and what may the meaning of this error?