Evil Bro wrote: > > > Counting can be done elegantly by 'filter' and 'length': > I figured out the following code after posting: > > solve d = length [(y,x) | x <- [2..d], y <- [1..(x-1)], gcd x y == 1] > main = print (solve 1000000) > > However when running it, it gave an answer of -1255316543. How on earth can > a length be negative?
Yu got an integer overflow - length returns an Int. You can use Data.List.genericLength instead, however, which can return its result in any Num instance. (In particular, Integer works) > import Data.List > > solve :: Integer -> Integer > solve d = genericLength [(y,x) | x <- [2..d], y <- [1..(x-1)], gcd x y == 1] > > main = print (solve 1000000) (Note: untested.) HTH, Bertram _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
