27/07/2011 9:47 AM, Jeff Lasslett kirjutas:
Also, if I understand correctly, solutions 1 & 2 will only produce one pair, whereas solution 3 (based on list comprehensions) will produce all pairs that sum to the total.
Correct, though it discards them in the end and only returns a Bool. That it does collect all the answers (before discarding) is probably why it has such a memory hit.
sumCheck1 _ [] _ = Nothing sumCheck1 total (x:xs) ys = if total' == Nothing then sumCheck total xs ys else return (x,(ys!!(fromJust total'))) where total' = elemIndex (total-x) ys
sumCheck2 total (x:xs) ys = let diff = total - x in if elem diff ys then Just (x,diff) else sumCheck total xs ys
sumCheck3 i as bs = not $ null [(x,y) | x <- as, y <- bs, x+y==i ]