Solution for largest-series-product

Author: qmenoret

largest-series-product/README.md

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+# Largest Series Product
+
+Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.
+
+For example, for the input `'1027839564'`, the largest product for a
+series of 3 digits is 270 (9 * 5 * 6), and the largest product for a
+series of 5 digits is 7560 (7 * 8 * 3 * 9 * 5).
+
+Note that these series are only required to occupy *adjacent positions*
+in the input; the digits need not be *numerically consecutive*.
+
+For the input `'73167176531330624919225119674426574742355349194934'`,
+the largest product for a series of 6 digits is 23520.
+
+
+## Getting Started
+
+For installation and learning resources, refer to the
+[exercism help page](http://exercism.io/languages/haskell).
+
+## Running the tests
+
+To run the test suite, execute the following command:
+
+```bash
+stack test
+```
+
+#### If you get an error message like this...
+
+```
+No .cabal file found in directory
+```
+
+You are probably running an old stack version and need
+to upgrade it.
+
+#### Otherwise, if you get an error message like this...
+
+```
+No compiler found, expected minor version match with...
+Try running "stack setup" to install the correct GHC...
+```
+
+Just do as it says and it will download and install
+the correct compiler version:
+
+```bash
+stack setup
+```
+
+## Running *GHCi*
+
+If you want to play with your solution in GHCi, just run the command:
+
+```bash
+stack ghci
+```
+
+## Feedback, Issues, Pull Requests
+
+The [exercism/xhaskell](https://github.com/exercism/xhaskell) repository on
+GitHub is the home for all of the Haskell exercises.
+
+If you have feedback about an exercise, or want to help implementing a new
+one, head over there and create an issue.  We'll do our best to help you!
+
+## Source
+
+A variation on Problem 8 at Project Euler [http://projecteuler.net/problem=8](http://projecteuler.net/problem=8)
+
+## Submitting Incomplete Problems
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+

largest-series-product/largest-series-product.cabal

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+-- This file has been generated from package.yaml by hpack version 0.15.0.
+--
+-- see: https://github.com/sol/hpack
+
+name:           largest-series-product
+version:        0.0.0
+build-type:     Simple
+cabal-version:  >= 1.10
+
+library
+  hs-source-dirs:
+      src
+  build-depends:
+      base
+  exposed-modules:
+      Series
+  other-modules:
+      Paths_largest_series_product
+  default-language: Haskell2010
+
+test-suite test
+  type: exitcode-stdio-1.0
+  main-is: Tests.hs
+  hs-source-dirs:
+      test
+  build-depends:
+      base
+    , largest-series-product
+    , hspec
+  default-language: Haskell2010

largest-series-product/package.yaml

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+name: largest-series-product
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: Series
+  source-dirs: src
+  dependencies:
+  # - foo       # List here the packages you
+  # - bar       # want to use in your solution.
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - largest-series-product
+      - hspec

largest-series-product/src/Series.hs

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+module Series (largestProduct) where
+
+import Data.Char
+import Data.Maybe
+
+largestProduct :: Int -> String -> Maybe Integer
+largestProduct size xs  | length xs >= size && onlyDigit && size >= 0 = reccur its size xs
+                        | otherwise         = Nothing
+    where
+        onlyDigit = all isDigit xs
+        l = length xs
+        its = l - size + 1
+
+reccur :: Int -> Int -> String -> Maybe Integer
+reccur 0 _ _ = Just 0
+reccur its size xs = if p > next then p else next
+    where
+        p = Just . fromIntegral . product $ map digitToInt (take size xs)
+        next = reccur (its - 1 ) size $ tail xs

largest-series-product/stack.yaml

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+resolver: lts-8.2

largest-series-product/test/Tests.hs

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+{-# OPTIONS_GHC -fno-warn-type-defaults #-}
+
+import Test.Hspec        (Spec, describe, it, shouldBe)
+import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)
+
+import Series (largestProduct)
+
+main :: IO ()
+main = hspecWith defaultConfig {configFastFail = True} specs
+
+specs :: Spec
+specs = describe "largest-series-product" $
+
+    -- Test cases adapted from `exercism/x-common/largest-series-product.json`
+    -- on 2016-07-27.
+
+    describe "largestProduct" $ do
+
+      it "can find the largest product of 2 with numbers in order" $
+        largestProduct 2 "0123456789"
+        `shouldBe` Just 72
+
+      it "can find the largest product of 2" $
+        largestProduct 2 "576802143"
+        `shouldBe` Just 48
+
+      it "finds the largest product if span equals length" $
+        largestProduct 2 "29"
+        `shouldBe` Just 18
+
+      it "can find the largest product of 3 with numbers in order" $
+        largestProduct 3 "0123456789"
+        `shouldBe` Just 504
+
+      it "can find the largest product of 3" $
+        largestProduct 3 "1027839564"
+        `shouldBe` Just 270
+
+      it "can find the largest product of 5 with numbers in order" $
+        largestProduct 5 "0123456789"
+        `shouldBe` Just 15120
+
+      it "can get the largest product of a big number" $
+        largestProduct 6 "73167176531330624919225119674426574742355349194934"
+        `shouldBe` Just 23520
+
+      it "can get the largest product of a big number II" $
+        largestProduct 6 "52677741234314237566414902593461595376319419139427"
+        `shouldBe` Just 28350
+
+      it "can get the largest product of a big number (Project Euler)" $
+        largestProduct 13 "73167176531330624919225119674426574742355349194934\
+                          \96983520312774506326239578318016984801869478851843\
+                          \85861560789112949495459501737958331952853208805511\
+                          \12540698747158523863050715693290963295227443043557\
+                          \66896648950445244523161731856403098711121722383113\
+                          \62229893423380308135336276614282806444486645238749\
+                          \30358907296290491560440772390713810515859307960866\
+                          \70172427121883998797908792274921901699720888093776\
+                          \65727333001053367881220235421809751254540594752243\
+                          \52584907711670556013604839586446706324415722155397\
+                          \53697817977846174064955149290862569321978468622482\
+                          \83972241375657056057490261407972968652414535100474\
+                          \82166370484403199890008895243450658541227588666881\
+                          \16427171479924442928230863465674813919123162824586\
+                          \17866458359124566529476545682848912883142607690042\
+                          \24219022671055626321111109370544217506941658960408\
+                          \07198403850962455444362981230987879927244284909188\
+                          \84580156166097919133875499200524063689912560717606\
+                          \05886116467109405077541002256983155200055935729725\
+                          \71636269561882670428252483600823257530420752963450"
+        `shouldBe` Just 23514624000
+
+      it "reports zero if the only digits are zero" $
+        largestProduct 2 "0000"
+        `shouldBe` Just 0
+
+      it "reports zero if all spans include zero" $
+        largestProduct 3 "99099"
+        `shouldBe` Just 0
+
+      it "rejects span longer than string length" $
+        largestProduct 4 "123"
+        `shouldBe` Nothing
+
+      it "reports 1 for empty string and empty product (0 span)" $
+        largestProduct 0 ""
+        `shouldBe` Just 1
+
+      it "reports 1 for nonempty string and empty product (0 span)" $
+        largestProduct 0 "123"
+        `shouldBe` Just 1
+
+      it "rejects empty string and nonzero span" $
+        largestProduct 1 ""
+        `shouldBe` Nothing
+
+      it "rejects invalid character in digits" $
+        largestProduct 2 "1234a5"
+        `shouldBe` Nothing
+
+      it "rejects negative span" $
+        largestProduct (-1) "12345"
+        `shouldBe` Nothing