i like this solve, before that i don't know about StringBuilder but now i know about it and i know it's best practice when we want to editing on the String cause its no creatint a new object in every time we editing in the String but it is editing on the same object, so its good for performance and efficiency and don't take more space from the Heap memory.

Trying the same (to my eyes) code, I keep getting a 'cannot find symbol' error on variable imp? (Never mind, found the typo, it was variable 'inp' ...)

It is clever, but not the best solution as no one understands with a brief look what's going on.

Does not work for another input. E.g. [2,-2, 0]

You are absolutely right, there is no need for this

I believe in that case kata would be higher than 7

What if the initial list have a boolean?

Thanks for the advice, beginner at codewars, haven't learned the local rules yet )

Thx. I believe it could be refactored even more, but have no time for this...
By the way, you may just press the buttons "Best Practices" and "Clever". Usually, comments are used to ask something or add some information.

Nice solution

Concatenation is way more readable and it might even be the tiniest amount more efficient