Euler #8 in Haskell

README.md

This a solution for the euler problem #8. It differs by repeating the provided string 4096 times, thus running on a string with 4.096.000 (4M) characters.

running

Assuming ghc is available, just type make.

This'll build a binary and runs the solution on the 4M string. On my machine, this takes about 0.4 seconds.

Euler-simple.hs

module Main where

import           Data.Char
import           Data.List

main :: IO ()
main = print
  . maximum . map product
  . filter((==13) . length) . map (take 13) . tails
  . map digitToInt
  $ "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450"

Euler.hs

module Main where

import           Data.Char

import qualified Data.ByteString.Char8 as T

type Str = T.ByteString

main :: IO ()
main = print $ maximum . asDigits . sliding 13 $ largeNumber

asDigits :: [Str] -> [Int]
asDigits = map (product . map digitToInt . T.unpack)

sliding :: Int -> Str -> [Str]
sliding n = filter nonZero . filter complete . map (T.take n) . T.tails
  where
    nonZero  = T.all (/='0')
    complete = (==n) . T.length

largeNumber :: Str
largeNumber = T.concat $ replicate 4096 $ T.pack number

number :: String
number = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450"

Makefile

module := Euler

time: ${module}
	time ./${module}

${module}: ${module}.hs
	ghc -O2 -Wall ${module}.hs

clean:
	-rm ${module} ${module}.hi ${module}.o

.PHONY: time clean