That would be a red flag for me in most cases, as the person being interviewed. If the interview is to gauge my knowledge of Javascript, then using sets should be in my favor since I'm using the most optimized approach to demonstrate I know the language well and can adequately do the job. If it's "not acceptable", then what is the goal there? To wrack my brain as part of some pseudo intelligence test? Shall we break it down to 1s and 0s too?