Add largest-series-product exercise

config.json

@@ -29,7 +29,8 @@
     "robot-simulator",
     "list-ops",
     "atbash-cipher",
-    "say"
+    "say",
+    "largest-series-product"
   ],
   "deprecated": [
 

elm-package.json

@@ -30,7 +30,8 @@
         "./exercises/robot-simulator",
         "./exercises/list-ops",
         "./exercises/atbash-cipher",
-        "./exercises/say"
+        "./exercises/say",
+        "./exercises/largest-series-product"
     ],
     "exposed-modules": [],
     "dependencies": {

exercises/largest-series-product/LargestSeriesProduct.elm

@@ -0,0 +1 @@
+module LargestSeriesProduct exposing (largestProduct)

exercises/largest-series-product/LargestSeriesProduct.example

@@ -0,0 +1,53 @@
+module LargestSeriesProduct exposing (largestProduct)
+
+import String
+
+
+largestProduct : Int -> String -> Maybe Int
+largestProduct length series =
+    if length < 0 then
+        Nothing
+    else if length == 0 then
+        Just 1
+    else
+        String.split "" series
+            |> List.map String.toInt
+            |> combineResults
+            |> Result.toMaybe
+            |> Maybe.map
+                (takeRuns length
+                    >> List.map List.product
+                    >> List.maximum
+                )
+            |> joinMaybe
+
+
+takeRuns : Int -> List a -> List (List a)
+takeRuns size items =
+    let
+        candidate =
+            List.take size items
+    in
+        if List.length candidate < size || size < 1 then
+            []
+        else
+            candidate :: takeRuns size (List.drop 1 items)
+
+
+
+-- inlined from Results.Extra and Maybe.Extra
+
+
+combineResults : List (Result x a) -> Result x (List a)
+combineResults =
+    List.foldr (Result.map2 (::)) (Ok [])
+
+
+joinMaybe : Maybe (Maybe a) -> Maybe a
+joinMaybe mx =
+    case mx of
+        Just x ->
+            x
+
+        Nothing ->
+            Nothing

exercises/largest-series-product/LargestSeriesProductTests.elm

@@ -0,0 +1,49 @@
+module Main exposing (..)
+
+import ElmTest exposing (..)
+import LargestSeriesProduct exposing (largestProduct)
+
+
+tests : Test
+tests =
+    suite "largestProduct"
+        [ test "can find the largest product of 2 with numbers in order"
+            (assertEqual (Just 72) (largestProduct 2 "0123456789"))
+        , test "can find the largest product of 2"
+            (assertEqual (Just 48) (largestProduct 2 "576802143"))
+        , test "finds the largest product if span equals length"
+            (assertEqual (Just 18) (largestProduct 2 "29"))
+        , test "can find the largest product of 3 with numbers in order"
+            (assertEqual (Just 504) (largestProduct 3 "0123456789"))
+        , test "can find the largest product of 3"
+            (assertEqual (Just 270) (largestProduct 3 "1027839564"))
+        , test "can find the largest product of 5 with numbers in order"
+            (assertEqual (Just 15120) (largestProduct 5 "0123456789"))
+        , test "can get the largest product of a big number"
+            (assertEqual (Just 23520) (largestProduct 6 "73167176531330624919225119674426574742355349194934"))
+        , test "can get the largest product of a big number II"
+            (assertEqual (Just 28350) (largestProduct 6 "52677741234314237566414902593461595376319419139427"))
+        , test "can get the largest product of a big number (Project Euler)"
+            (assertEqual (Just 23514624000) (largestProduct 13 "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450"))
+        , test "reports zero if the only digits are zero"
+            (assertEqual (Just 0) (largestProduct 2 "0000"))
+        , test "reports zero if all spans include zero"
+            (assertEqual (Just 0) (largestProduct 3 "99099"))
+        , test "rejects span longer than string length"
+            (assertEqual Nothing (largestProduct 4 "123"))
+        , test "reports 1 for empty string and empty product (0 span)"
+            (assertEqual (Just 1) (largestProduct 0 ""))
+        , test "reports 1 for nonempty string and empty product (0 span)"
+            (assertEqual (Just 1) (largestProduct 0 "123"))
+        , test "rejects empty string and nonzero span"
+            (assertEqual Nothing (largestProduct 1 ""))
+        , test "rejects invalid character in digits"
+            (assertEqual Nothing (largestProduct 2 "1234a5"))
+        , test "rejects negative span"
+            (assertEqual Nothing (largestProduct -1 "12345"))
+        ]
+
+
+main : Program Never
+main =
+    runSuite tests

exercises/largest-series-product/elm-package.json

@@ -0,0 +1,15 @@
+{
+    "version": "2.0.0",
+    "summary": "Exercism problems in Elm.",
+    "repository": "https://github.com/exercism/xelm.git",
+    "license": "BSD3",
+    "source-directories": [
+        "."
+    ],
+    "exposed-modules": [],
+    "dependencies": {
+        "elm-community/elm-test": "1.0.0 <= v < 2.0.0",
+        "elm-lang/core": "4.0.0 <= v < 5.0.0"
+    },
+    "elm-version": "0.17.0 <= v < 0.18.0"
+}

exercises/largest-series-product/runtests.bat

@@ -0,0 +1,4 @@
+@echo off
+for %%f in (*Tests.elm) do (
+  elm-make %%f --yes --output build.js && node build.js
+)

exercises/largest-series-product/runtests.sh

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+elm-make *Tests.elm --yes --output build.js && node build.js