On Nov 27, 2007 8:44 PM, Andrew Coppin
Andrew Coppin wrote:
Also, I'm stuck with problem #10. (Find the sum of all primes less than 1 million.) I've let the program run for well over 15 minutes, and still no answer is forthcomming. It's implemented using the same primes function as above, with a simple filter and sum. (The type has to be changed to [Word64] to avoid overflowing the result though.) The other guy claims to have a C solution that takes 12 ms. There's a hell of a difference between 12 ms and over half an hour...(!) Clearly something is horribly wrong here. Uh... help?
I just let it run to completion. Took 25 minutes and 15 seconds to find the (correct) answer. I would have preferred it to take 12 ms...
FWIW the following code took 0.77s on my machine: primes :: [Integer] primes = 2 : filter (null . primeFactors) [3,5..] primeFactors :: Integer-> [Integer] primeFactors n = factor n primes where factor m (p:ps) | p*p > m = [] | m `mod` p == 0 = p : factor (m `div` p) (p:ps) | otherwise = factor m ps main = print ( sum ( takeWhile (< 1000000) primes ) ) -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862