Solution to Google Code Jam 2014. Qualification-A Magic Trick https://code.google.com/codejam/contest/2974486/dashboard#s=p0

magic.hs

module Main where

import Control.Monad
import Data.List

-- https://code.google.com/codejam/contest/dashboard?c=2974486#s=p0
-- Input and output with standard redirection operators

-- Unless otherwise indicated, all modules used are either bundled with
-- the Haskell Platform (http://hackage.haskell.org/platform/) or available
-- as a separate download from Hackage (http://hackage.haskell.org/).

solve :: [Int] -> [Int] -> String
solve a b
  | l == 1 = show $ head common
  | l > 1  = "Bad magician!"
  | otherwise = "Volunteer cheated!"
  where common = a `intersect` b
        l = length common

main :: IO ()
main = do
  t <- getLine
  forM_ [1..read t :: Int] $ \i -> do
    choice1 <- fmap read getLine
    initial <- replicateM 4 $ fmap (map read . words) getLine
    choice2 <- fmap read getLine
    final <- replicateM 4 $ fmap (map read . words) getLine
    let r1 = initial !! (choice1 - 1)
        r2 = final !! (choice2 - 1)
    putStrLn $ concat ["Case #", show i, ": ", solve r1 r2]