[sfn42]

> It unconditionally uses a hashset regardless of input.

This follows what I like to call macro optimization. I don't care if a hash set is slightly slower for small inputs. Small inputs are negligibly fast anyway. The hash set solution just works for almost any dataset. Either it's too small to give a crap, midsized and hash set is best, or huge and hash set is still pretty much best.

That's why we default to the best time/space complexity. Once in a blue moon someone might have an obscure usecase where micro optimizing for small datasets makes sense somehow, for the vast majority of use cases this solution is best.