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You can reach the person managing the list at beginners-ow...@haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Beginners digest..." Today's Topics: 1. Re: list doesn't end (Francesco Ariis) ---------------------------------------------------------------------- Message: 1 Date: Mon, 25 Nov 2019 14:20:24 +0100 From: Francesco Ariis <fa...@ariis.it> To: beginners@haskell.org Subject: Re: [Haskell-beginners] list doesn't end Message-ID: <20191125132024.ga16...@x60s.casa> Content-Type: text/plain; charset=utf-8 On Mon, Nov 25, 2019 at 08:55:17AM +0100, Alexander Chen wrote: > Hi Francesco, > > Their is a ^2, ^3, ^4 in the lists, respectively. > > see https://projecteuler.net/problem=87 This runs reasonably fast even on my old 32bit machine: import qualified Data.Set as S import Data.Numbers.Primes sol72 :: Integer -> Int sol72 l = S.size . S.fromList $ [(x+y+z) | x <- p2, y <- p3, z <- p4, x+y+z < l] where f :: Integer -> [Integer] f n = takeWhile (< l) $ map (^n) primes p2, p3, p4 :: [Integer] p2 = f 2 p3 = f 3 p4 = f 4 λ> sol72 (50 * 10^6) 1097343 Notice how the lengths for lists p2, p3 and p4 are actually 908, 73 and 23! -F ------------------------------ Subject: Digest Footer _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners ------------------------------ End of Beginners Digest, Vol 137, Issue 12 ******************************************