{-

- Solution to Project Euler problem 39

- Copyright (c) Project Nayuki. All rights reserved.

-

- https://www.nayuki.io/page/project-euler-solutions

- https://github.com/nayuki/Project-Euler-solutions

-}

import Data.List (foldl1')

main = putStrLn (show ans)

ans = argMax numRightTriangles [1..1000]

-- Number of right triangles with perimeter p and integer side lengths.

numRightTriangles :: Int -> Int

numRightTriangles p = sum [1 | a <- [1..p], b <- [a..(div (p-a) 2)], let c = p-a-b in a*a + b*b == c*c]

-- The earliest element x in the list such that (f x) >= (f y) for each element y in the list.

argMax :: Ord b => (a -> b) -> [a] -> a

argMax f = foldl1' (\x y -> if (f y) > (f x) then y else x)