@akar-0
Then it would not become 8 kyu level. Suggesting to add a "without loops" requirement in the instruction or make reduce kyu level.

I have no clue why I started this by creating an ArrayList. It is just bloody superfluous...
Anyhoo, did a quick refactor to remove the ArrayList and simply use an incremental int.

No, this is not a proper way to do it. One could use a loop, it depends on what there is in it. And making it a kata requirement would require to enforce to forbid the use of loops, which can hardly be done in some language, and would not make sense. If one's code times out, he needs to find a better way to solve the kata, there's already Expect large Inputs!, that's enough.