2008/3/31, Bruno Carnazzi <[EMAIL PROTECTED]>: > Dears Haskellers, > > As an Haskell newbie, I'm learning Haskell by trying to resolve Euler > Project problems (http://projecteuler.net/ ). I'm hanging on problem > 14 (Collatz problem). > > I've written the following program... Which does not end in a reasonable > time :( > My algorithm seems ok to me but I see that memory consumption is gigantic... > Is this a memory problem with Data.Map ? Or an infinite loop ? (Where ?) > In a more general way, how can I troubleshoot these kind of problem ?
Others have pointed potential source of memory leaks, but I must say that using Data.Map for the cache in the first place appear to me as a very bad idea... Data.Map by nature take much more place than necessary. You have an integer index, why not use an array instead ? > import Data.Array > import Data.List > import Data.Ord > > syrs n = a > where a = listArray (1,n) $ 0:[ syr n x | x <- [2..n]] > syr n x = if x' <= n then a ! x' else 1 + syr n x' > where x' = if even x then x `div` 2 else 3 * x + 1 > > main = print $ maximumBy (comparing snd) $ assocs $ syrs 1000000 This solution takes 2 seconds (on my machine) to resolve the problem. On the other hand, now that I have read your solution, I see that using Map was the least of the problem... All those Map.map, while retaining the original Map... Your solution is too clever (twisted) for its own good, I suggest you aim for simplicity next time. -- Jedaï _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
