60 lines
2.9 KiB
Haskell
60 lines
2.9 KiB
Haskell
-- The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
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--
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-- 73167176531330624919225119674426574742355349194934
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-- 96983520312774506326239578318016984801869478851843
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-- 85861560789112949495459501737958331952853208805511
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-- 12540698747158523863050715693290963295227443043557
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-- 66896648950445244523161731856403098711121722383113
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-- 62229893423380308135336276614282806444486645238749
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-- 30358907296290491560440772390713810515859307960866
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-- 70172427121883998797908792274921901699720888093776
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-- 65727333001053367881220235421809751254540594752243
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-- 52584907711670556013604839586446706324415722155397
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-- 53697817977846174064955149290862569321978468622482
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-- 83972241375657056057490261407972968652414535100474
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-- 82166370484403199890008895243450658541227588666881
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-- 16427171479924442928230863465674813919123162824586
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-- 17866458359124566529476545682848912883142607690042
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-- 24219022671055626321111109370544217506941658960408
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-- 07198403850962455444362981230987879927244284909188
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-- 84580156166097919133875499200524063689912560717606
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-- 05886116467109405077541002256983155200055935729725
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-- 71636269561882670428252483600823257530420752963450
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--
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-- Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
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import Data.Char (digitToInt)
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nDigitProduct :: Int -> String -> Int
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nDigitProduct n s
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| length s < n = -1
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| otherwise = max (product (map digitToInt (take n s))) (nDigitProduct n (tail s))
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main = do
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let s =
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"73167176531330624919225119674426574742355349194934"
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++ "96983520312774506326239578318016984801869478851843"
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++ "85861560789112949495459501737958331952853208805511"
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++ "12540698747158523863050715693290963295227443043557"
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++ "66896648950445244523161731856403098711121722383113"
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++ "62229893423380308135336276614282806444486645238749"
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++ "30358907296290491560440772390713810515859307960866"
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++ "70172427121883998797908792274921901699720888093776"
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++ "65727333001053367881220235421809751254540594752243"
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++ "52584907711670556013604839586446706324415722155397"
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++ "53697817977846174064955149290862569321978468622482"
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++ "83972241375657056057490261407972968652414535100474"
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++ "82166370484403199890008895243450658541227588666881"
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++ "16427171479924442928230863465674813919123162824586"
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++ "17866458359124566529476545682848912883142607690042"
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++ "24219022671055626321111109370544217506941658960408"
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++ "07198403850962455444362981230987879927244284909188"
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++ "84580156166097919133875499200524063689912560717606"
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++ "05886116467109405077541002256983155200055935729725"
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++ "71636269561882670428252483600823257530420752963450"
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result = nDigitProduct 13 s
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putStrLn $
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"Project Euler, Problem 8\n"
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++ "Answer: "
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++ show result
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