codeforces - 47 - A (hs)

A.hs

{-# OPTIONS_GHC -O2 -XNoMonomorphismRestriction #-}
{-# LANGUAGE BangPatterns #-}
{-(c) gorlum0 [at] gmail.com-}
import Control.Monad (forM_)

triangular = takeWhile (<=500) $ scanl1 (+) [1..]

main = do
    ls <- lines `fmap` getContents
    let xs = map read ls
    forM_ [x `elem` triangular | x <- xs] $
        putStrLn . (\p -> if p then "YES" else "NO")