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)
+        )