Day 3

src/Days/D03.hs

@@ -0,0 +1,34 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+
+module Days.D03 where
+
+import Data.Char (ord)
+import Data.List (intersect)
+import Data.List.Extra (chunksOf)
+import Lib (Day (StringDay), definitive)
+
+type Intermediate = [String]
+
+halves :: [a] -> ([a], [a])
+halves l = splitAt (length l `div` 2) l
+
+priority :: Char -> Int
+priority c =
+    let o = ord c
+     in if o < ord 'a'
+            then o - ord 'A' + 26 + 1
+            else o - ord 'a' + 1
+
+part1 :: [String] -> Int
+part1 = sum . map (priority . head . uncurry intersect . halves)
+
+part2 :: [String] -> Int
+part2 = sum . map (priority . head . foldl1 intersect) . chunksOf 3
+
+day :: Day
+day =
+    StringDay
+        ( \s ->
+            let l = lines s
+             in Right (definitive $ part1 l, definitive $ part2 l)
+        )

src/Lib.hs

@@ -4,13 +4,13 @@
 
 module Lib where
 
-import Util (both, dupe)
+import Util (both)
 
 import Data.Function ((&))
 import Data.Text qualified as T
 import Data.Text.IO qualified as T
 import Data.Void (Void)
-import Text.Megaparsec qualified as M (Parsec, eof, errorBundlePretty, parse, sepEndBy1)
+import Text.Megaparsec qualified as M (Parsec, eof, errorBundlePretty, parse)
 
 data Answer where
     Answer :: (Show a) => a -> Answer

src/Print.hs

@@ -1,7 +1,6 @@
 module Print where
 
-import Data.Maybe (fromMaybe)
-import Lib (DayResult, PuzzleError (..))
+import Lib (DayResult)
 import Text.Printf (printf)
 
 printDR :: Int -> DayResult -> IO ()

src/Util.hs

@@ -5,6 +5,3 @@ dupe a = (a, a)
 
 both :: (a -> b) -> (a, a) -> (b, b)
 both f ~(x, y) = (f x, f y)
-
-mapSnd :: (b -> c) -> (a, b) -> (a, c)
-mapSnd f (a, b) = (a, f b)