problem8.hs

import Data.Char
import Data.List
import GHC.Exts

input:: [Char]
input = filter (\c -> isDigit(c)) "73167176531330624919225119674426574742355349194934"
        ++ "96983520312774506326239578318016984801869478851843"
        ++ "85861560789112949495459501737958331952853208805511"
        ++ "12540698747158523863050715693290963295227443043557"
        ++ "66896648950445244523161731856403098711121722383113"
        ++ "62229893423380308135336276614282806444486645238749"
        ++ "30358907296290491560440772390713810515859307960866"
        ++ "70172427121883998797908792274921901699720888093776"
        ++ "65727333001053367881220235421809751254540594752243"
        ++ "52584907711670556013604839586446706324415722155397"
        ++ "53697817977846174064955149290862569321978468622482"
        ++ "83972241375657056057490261407972968652414535100474"
        ++ "82166370484403199890008895243450658541227588666881"
        ++ "16427171479924442928230863465674813919123162824586"
        ++ "17866458359124566529476545682848912883142607690042"
        ++ "24219022671055626321111109370544217506941658960408"
        ++ "07198403850962455444362981230987879927244284909188"
        ++ "84580156166097919133875499200524063689912560717606"
        ++ "05886116467109405077541002256983155200055935729725"
        ++ "71636269561882670428252483600823257530420752963450"


windowed :: Int -> [a] -> [[a]]
windowed w ls = reverse (win [] ls)
                where 
                    win acc [] = acc
                    win acc lss = if (length lss < w) then
                                acc 
                                else 
                                    win ((take w lss) : acc) (tail lss)


windowTupled :: [(Int, [Char])]
windowTupled = [(product (map digitToInt xs), xs) | xs <- (windowed 13 input)]

result = fst $ last (sortBy(\xs -> \ys -> compare (fst xs) (fst ys)) windowTupled)