30 May
2007
30 May
'07
1:35 p.m.
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