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Copy path008_largest_product_in_a_series.hs
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008_largest_product_in_a_series.hs
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-- Find the greatest product of five consecutive digits in the 1000-digit number.
--
-- 73167176531330624919225119674426574742355349194934
-- 96983520312774506326239578318016984801869478851843
-- 85861560789112949495459501737958331952853208805511
-- 12540698747158523863050715693290963295227443043557
-- 66896648950445244523161731856403098711121722383113
-- 62229893423380308135336276614282806444486645238749
-- 30358907296290491560440772390713810515859307960866
-- 70172427121883998797908792274921901699720888093776
-- 65727333001053367881220235421809751254540594752243
-- 52584907711670556013604839586446706324415722155397
-- 53697817977846174064955149290862569321978468622482
-- 83972241375657056057490261407972968652414535100474
-- 82166370484403199890008895243450658541227588666881
-- 16427171479924442928230863465674813919123162824586
-- 17866458359124566529476545682848912883142607690042
-- 24219022671055626321111109370544217506941658960408
-- 07198403850962455444362981230987879927244284909188
-- 84580156166097919133875499200524063689912560717606
-- 05886116467109405077541002256983155200055935729725
-- 71636269561882670428252483600823257530420752963450
takeLastFive :: (Integral a) => a -> [a]
takeLastFive n = listFive (mod n 100000) []
listFive :: (Integral a) => a -> [a] -> [a]
listFive n l
| n < 10 = n : l
| otherwise = listFive (div n 10) ((mod n 10) : l)
largestProduct :: (Integral a) => a -> a
largestProduct n = largestProduct' n 0
largestProduct' :: (Integral a) => a -> a -> a
largestProduct' n best
| n < 10000 = best
| otherwise = largestProduct' (div n 10) (max best (mulList (takeLastFive n)))
mulList :: (Integral a) => [a] -> a
mulList list = foldr (\x y -> x * y) 1 list
main :: IO()
main = putStrLn $ show $ largestProduct 7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450