The second prime generator on this page http://www.haskell.org/haskellwiki/Prime_numbers is quick and easy. I keep it nearby for all those sudden attacks of needing to solve yet another projecteuler problem. -ljr Slavomir Kaslev wrote:
Hello,
I was just brushing my haskell-fu skills writing a solution for Google Treasure Hunt Problem 4. Hers is what it looks like:
primes = sieve [2..] where sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0]
sumOf n l = sum (take n l) : sumOf n (tail l)
find l = foldl1 aux l where aux (x:xs) (y:ys) | x == y = x : aux xs ys | x < y = aux xs (y:ys) | x > y = aux (x:xs) ys
puzzle = find (reverse [primes, p7, p17, p41, p541]) where p7 = sumOf 7 primes p17 = sumOf 17 primes p41 = sumOf 41 primes p541 = sumOf 541 primes
main = do mapM (\x -> putStrLn $ show x) puzzle
While the code is quite readable and straight forward it is as slow as tortoise with four legs broken. What optimizations would you suggest, while still keeping the code clear and highlevel?
Thank you in advance.
Cheers.