mutation of the input? (or anything similar in C++)

I'm sorry but how can my code alter what the tests expects?

Edit: apparently by using const cast, now it works, thanks

The C++ version is working perfectly fine. Your code must be causing this.

The random tests for c++ are broken. The test will give as expected a string composed of a bunch of words glued together instead of an actual word in the string.
Example:
Input string: "stteie r oibtraeoeet i hoaseacrzake kaaoasutoc katidsb pepf uusprtorh rcietsp nps euc ootzpginasbnebkrd se bnhleay kiahpmaaprtkayaa"
Expected: "bnhleaykiahpmaaprtkayaa"

Yep, looks much more sexier, thanks.