Added Largest Series Product exercise

config.json

@@ -159,6 +159,13 @@
       "topics": [
         "maps"
       ]
+    },
+    {
+      "slug": "largest-series-product",
+      "difficulty": 1,
+      "topics": [
+        "strings"
+      ]
     }
   ],
   "deprecated": [

exercises/largest-series-product/bower.json

@@ -0,0 +1,16 @@
+{
+  "name": "largest-series-product",
+  "ignore": [
+    "**/.*",
+    "node_modules",
+    "bower_components",
+    "output"
+  ],
+  "dependencies": {
+    "purescript-prelude": "^3.0.0"
+  },
+  "devDependencies": {
+    "purescript-psci-support": "^3.0.0",
+    "purescript-test-unit": "^11.0.0"
+  }
+}

exercises/largest-series-product/examples/src/LargestSeriesProduct.purs

@@ -0,0 +1,31 @@
+module LargestSeriesProduct
+  ( largestProduct
+  ) where
+
+import Prelude
+import Data.Array (drop, length, take, (:))
+import Data.Foldable (maximum, product)
+import Data.Int (fromString)
+import Data.Maybe (Maybe(..))
+import Data.String (singleton, toCharArray)
+import Data.Traversable (sequence)
+
+spans :: forall a. Int -> Array a -> Array (Array a)
+spans n a
+  | length a < n = []
+  | otherwise    = take n a : spans n (drop 1 a)
+
+toIntArray :: String -> Maybe (Array Int)
+toIntArray = toCharArray
+             >>> map (singleton >>> fromString) 
+             >>> sequence
+
+largestProduct :: String -> Int -> Maybe Int
+largestProduct digits span
+  | span == 0 = Just 1
+  | span < 0  = Nothing
+  | otherwise = do
+    is <- toIntArray digits
+    spans span is
+      # map product
+      # maximum

exercises/largest-series-product/src/LargestSeriesProduct.purs

@@ -0,0 +1,3 @@
+module LargestSeriesProduct
+  ( largestProduct
+  ) where

exercises/largest-series-product/test/Main.purs

@@ -0,0 +1,73 @@
+module Test.Main where
+
+import Prelude
+import Control.Monad.Eff (Eff)
+import Data.Maybe (Maybe(..))
+import Test.Unit.Assert as Assert
+import Test.Unit (suite, test)
+import Test.Unit.Main (runTest)
+import LargestSeriesProduct (largestProduct)
+
+main :: Eff _ Unit
+main = runTest do
+  suite "LargestSeriesProduct.largestProduct" do
+
+    test "finds the largest product if span equals length" $
+      Assert.equal (Just 18)
+                   (largestProduct "29" 2)
+
+    test "can find the largest product of 2 with numbers in order" $
+      Assert.equal (Just 72)
+                   (largestProduct "0123456789" 2)
+
+    test "can find the largest product of 2" $
+      Assert.equal (Just 48)
+                   (largestProduct "576802143" 2)
+
+    test "can find the largest product of 3 with numbers in order" $
+      Assert.equal (Just 504)
+                   (largestProduct "0123456789" 3)
+
+    test "can find the largest product of 3" $
+      Assert.equal (Just 270)
+                   (largestProduct "1027839564" 3)
+
+    test "can find the largest product of 5 with numbers in order" $
+      Assert.equal (Just 15120)
+                   (largestProduct "0123456789" 5)
+
+    test "can get the largest product of a big number" $
+      Assert.equal (Just 23520)
+                   (largestProduct "73167176531330624919225119674426574742355349194934" 6)
+
+    test "reports zero if the only digits are zero" $
+      Assert.equal (Just 0)
+                   (largestProduct "0000" 2)
+
+    test "reports zero if all spans include zero" $
+      Assert.equal (Just 0)
+                   (largestProduct "99099" 3)
+
+    test "rejects span longer than string length" $
+      Assert.equal Nothing
+                   (largestProduct "123" 4)
+
+    test "reports 1 for empty string and empty product (0 span)" $
+      Assert.equal (Just 1)
+                   (largestProduct "" 0)
+
+    test "reports 1 for nonempty string and empty product (0 span)" $
+      Assert.equal (Just 1)
+                   (largestProduct "123" 0)
+
+    test "rejects empty string and nonzero span" $
+      Assert.equal Nothing
+                   (largestProduct "" 1)
+
+    test "rejects invalid character in digits" $
+      Assert.equal Nothing
+                   (largestProduct "1234a5" 2)
+
+    test "rejects negative span" $
+      Assert.equal Nothing
+                   (largestProduct "12345" (-1))