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Today's Topics:
1. Re: list doesn't end (Francesco Ariis)
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Message: 1
Date: Mon, 25 Nov 2019 14:20:24 +0100
From: Francesco Ariis <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] list doesn't end
Message-ID: <[email protected]>
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
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