src/Annans.hs

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+module Annans (main') where
+
+import qualified Data.ByteString.Lazy as BL
+import Data.List (sort)
+import Data.List.Split
+import Data.Text.Encoding (decodeUtf8)
+import Data.Text.Read (decimal)
+import Prelude
+
+largest3 :: [Int] -> [Int]
+largest3 = \case
+    a : b : c : rest ->
+        let [a', b', c'] = sort [a, b, c]
+         in go a' b' c' rest
+    xs -> sort xs
+  where
+    -- a <= b <= c
+    go a b c [] = [a, b, c]
+    go !a !b !c (!x : xs)
+        | x >= c = go b c x xs
+        | x >= b = go b x c xs
+        | x >= a = go x b c xs
+        | otherwise = go a b c xs
+
+parse :: BL.ByteString -> Int
+parse =
+    (\case (Right (x, _)) -> x)
+        . decimal
+        . decodeUtf8
+        . BL.toStrict
+
+parseAll :: BL.ByteString -> [[Int]]
+parseAll =
+    map (map parse)
+        . filter (not . null)
+        . splitOn [BL.empty]
+        . BL.split 0x0a
+
+main' :: IO ()
+main' =
+    main'' "aoc_2022_day01_large_input.txt"
+
+process :: BL.ByteString -> [Int]
+process = largest3 . map sum . parseAll
+
+main'' :: FilePath -> IO ()
+main'' file = do
+    [x1, x2, x3] <- process <$> BL.readFile file
+    print $ x3
+    print $ x1 + x2 + x3