Now assume that I have a set a with O(n) elements and a set b with O(1)
elements.

You can't have "O(1) elements" ... (A bound like O(..) talks about the worst case time/space of an operation.)

a `minusSet` b would take O(n) time and so would a `intersect` b.
If I'd use
    foldr (flip delFromSet) a (setToList b)
and
    [x | x <- setToList b, x `elementOf` a]
instead of a `minusSet` b and a `intersect` b, I would get away with O(log n)
time.

I think that you are mixing up worst case bounds O(..) with some specific case. I guess that you mean by "O(1) elements" a known and constant number of elements. However, in the worst case, this will degenerate to some "m" number of elements, and your function would take O(m*log n) time, i.e. much worse than O(n+m).

All the best,
 Daan.


Is this true?


Wolfgang

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