Problem 9

Project Euler haskell

http://projecteuler.net/index.php?section=problems&id=9

a + b + c = 1000 になるピタゴラス数 (a^2 + b^2 = c^2) を探して
a * b * c を求める。

main = (print . product . head ) touple
    where touple = [[a, b, 1000-a-b] | a <- [1..1000], b <- [1..(1000-a)], isPythagorean a b (1000-a-b)]

isPythagorean:: (Integral a) => a -> a -> a -> Bool
isPythagorean a b c | a <= b && b <= c = a ^ 2 + b ^ 2 == c ^ 2
                    | otherwise        = False

a = 200
b = 375
c = 425