1 files changed, 25 insertions, 0 deletions
diff --git a/2020/06-Custom_Customs/second.hs b/2020/06-Custom_Customs/second.hs
new file mode 100644
index 0000000..10d0ff4
--- /dev/null
+++ b/2020/06-Custom_Customs/second.hs
@@ -0,0 +1,25 @@
+-- requires cabal install --lib split Unique
+module Main (main) where
+
+import Control.Monad (void, when)
+import Data.List (intersect, foldl')
+import Data.List.Split (splitOn)
+import System.Exit (die)
+
+exampleExpectedOutput = 6
+
+parseInput :: String -> IO [String]
+parseInput filename = do
+  input <- readFile filename
+  return $ map (foldl' intersect ['a'..'z'] . lines) $ splitOn "\n\n" input
+
+compute :: [String] -> Int
+compute = sum . map length
+
+main :: IO ()
+main = do
+  example <- parseInput "example"
+  let exampleOutput = compute example
+  when  (exampleOutput /= exampleExpectedOutput)  (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute input