Solve 'Counting Duplicates Across Multiple Lists' kata

Author: borisskert

src/Duplicates.hs

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+module Duplicates where
+
+-- https://www.codewars.com/kata/6113c2dc3069b1001b8fdd05/train/haskell
+
+import Data.List (group, sort)
+
+countDuplicates :: [String] -> [Int] -> [Int] -> Int
+countDuplicates names ages heights =
+  sum
+    . map (subtract 1)
+    . filter (> 1)
+    . map length
+    . group
+    . sort
+    $ zip3 names ages heights

test/DuplicatesSpec.hs

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+module DuplicatesSpec where
+
+import Duplicates (countDuplicates)
+import Test.HUnit
+import Test.Hspec
+
+spec :: Spec
+spec = do
+  describe "Fixed Tests" $ do
+    it "Returns 0 if there are no duplicates" $ do
+      runTest
+        ["John", "Beth", "Beth", "Bill"]
+        [37, 23, 30, 46]
+        [183, 170, 165, 175]
+        0
+    it "Counts duplicates of one entry" $ do
+      runTest
+        ["John", "Beth", "Beth", "Beth", "Bill"]
+        [37, 23, 23, 23, 46]
+        [183, 170, 170, 170, 175]
+        2
+    it "Counts duplicates from multiple entries" $ do
+      runTest
+        ["Jack", "Ben", "Jack", "Ben", "Jack", "Jack"]
+        [25, 25, 34, 25, 25, 34]
+        [180, 180, 200, 180, 180, 200]
+        3
+
+runTest :: [String] -> [Int] -> [Int] -> Int -> Expectation
+runTest name age height expected = assertEqual msg expected actual
+  where
+    actual = countDuplicates name age height
+    msg = "Test Failed\n  " ++ showInput (name, age, height)
+
+showInput :: ([String], [Int], [Int]) -> String
+showInput (n, a, h) = unwords ["countDuplicates", show n, show a, show h]