pe9

pe9.hs

import Control.Monad

coprime a b = gcd a b == 1
istriple m n = coprime m n && odd (m - n) && (m > n) && m > 0 && n > 0

triple m n k = 
            let a = k * (m^2 - n^2)
                b = k * (2*m*n)
                c = k * (m^2 + n^2)
                in [a,b,c]

main = do
        let candidates = filter (uncurry istriple) $ join [[(m,n) | n <- [1..500]] | m <- [1..500]]
        print $ head $ dropWhile ((/=1000) . sum) $ join [[triple m n k | k <- [1..(1000-(m+n))]] | (m,n) <- candidates, (m+n) < 1000]