codeforces - 2 - A (hs)

A.hs

{-# OPTIONS_GHC -O2 -XNoMonomorphismRestriction #-}
{-# LANGUAGE BangPatterns #-}
{-(c) gorlum0 [at] gmail.com-}
import qualified Data.Map as M
import qualified Data.Set as S

splitEvery _ [] = []
splitEvery n xs = ys : splitEvery n xs'
    where (ys, xs') = splitAt n xs

winner :: [(String, Int)] -> String
winner rounds = f M.empty rounds'
    where
    rounds' = [(k, v) | (k, v) <- rounds, S.member k cands]

    game = M.fromListWith (+) rounds
    m = maximum $ M.elems game
    --- cands = S.fromList [k | (k, v) <- M.toList game, v == m]
    cands = M.keysSet $ M.filter (==m) game

    f :: M.Map String Int -> [(String, Int)] -> String
    f game ((k,v):xs)
        | n >= m    = k
        | otherwise = f game' xs
        where game' = M.insertWith (+) k v game
              Just n = M.lookup k game'

body :: [String] -> [String]
body [] = []
body (n:xs) = winner rounds : body xs'
    where
    n' = read n
    (ys, xs') = splitAt (n'*2) xs
    rounds = [(k, read v) | [k, v] <- splitEvery 2 ys]

main = do
    ws <- words `fmap` getContents
    mapM_ putStrLn $ body ws