BEasterEggs.hs

{-# OPTIONS_GHC -O2 -optc-O3 -optc-ffast-math -cpp #-}
{-# OPTIONS_GHC -funbox-strict-fields -fexcess-precision -monly-3-regs #-}
{-# LANGUAGE BangPatterns, OverloadedStrings, ScopedTypeVariables #-}
{-# LANGUAGE NoMonomorphismRestriction #-}
module Main where
import Control.Applicative
import Data.List
import Text.Printf

splitBy :: (a -> Bool) -> [a] -> [[a]]
splitBy p [] = []
splitBy p xs = a : (splitBy p $ dropWhile p $ b)
   where
     (a, b) = break p xs
 
split :: String -> [String]
split = splitBy (==' ')

-- input = lines <$> readFile "input.txt"
--input = lines <$> getContents
input = getContents

xs = "ROYGBIV" ++ xs
      

solve :: Int -> String
solve n = concat . take 1 $ [ zs | zs <- permutations $ ys, check zs]
    where ys = take n xs


check xs =  g ys
       where 
         n = 4
         f xs = (==n) . length . nub . take n $ xs
         g [x1,x2,x3,x4] = f [x1,x2,x3,x4]
         g xs = (f xs) && g (tail xs)
         ys = let as = take n xs in xs ++ as

f xs = (==n) . length . nub . take n $ xs
       where n = 4

g [x1,x2,x3,x4] = [f $ [x1,x2,x3,x4]]
g xs            = (f xs)  : g (tail xs)



rr :: String -> Int
rr = read


main :: IO ()
main = do { ns <- input
          ; printf "%s" . solve . rr $ ns
          }