solve 2022 day 3 pt 1 & 2

2022/README.md

@@ -2,7 +2,7 @@
 
 |  S  |  M  |  T  |  W  |  T  |  F  |  S   |
 | :-: | :-: | :-: | :-: | :-: | :-: | :--: |
-|     |     |     |     | [1] | [2] |   3  |
+|     |     |     |     | [1] | [2] |  [3] |
 |  4  |  5  |  6  |  7  |  8  |  9  |  10  |
 | 11  | 12  | 13  | 14  | 15  | 16  |  17  |
 | 18  | 19  | 20  | 21  | 22  | 23  |  24  |
@@ -10,3 +10,4 @@
 
 [1]: ./src/Aoc/Day1.hs
 [2]: ./src/Aoc/Day2.hs
+[3]: ./src/Aoc/Day3.hs

2022/aoc.cabal

@@ -27,6 +27,7 @@ library
   exposed-modules:
       Aoc.Day1
       Aoc.Day2
+      Aoc.Day3
   other-modules:
       Paths_aoc
   hs-source-dirs:
@@ -34,6 +35,8 @@ library
   ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
   build-depends:
       base >=4.7 && <5
+    , containers
+    , split
     , text
   default-language: Haskell2010
 
@@ -47,6 +50,8 @@ executable aoc-exe
   build-depends:
       aoc
     , base >=4.7 && <5
+    , containers
+    , split
     , text
   default-language: Haskell2010
 
@@ -61,5 +66,7 @@ test-suite aoc-test
   build-depends:
       aoc
     , base >=4.7 && <5
+    , containers
+    , split
     , text
   default-language: Haskell2010

2022/app/Main.hs

@@ -4,6 +4,7 @@ module Main (main) where
 import System.Environment (getArgs)
 import qualified Aoc.Day1
 import qualified Aoc.Day2
+import qualified Aoc.Day3
 
 main :: IO ()
 main = do
@@ -15,6 +16,7 @@ main = do
 
   let f = case day of 1 -> Aoc.Day1.solve
                       2 -> Aoc.Day2.solve
+                      3 -> Aoc.Day3.solve
                       _ -> error "unknown day"
 
   putStrLn $ show $ f part contents

2022/package.yaml

@@ -22,6 +22,8 @@ description:         Please see the README on GitHub at <https://github.com/sloa
 dependencies:
 - base >= 4.7 && < 5
 - text
+- containers
+- split
 
 ghc-options:
 - -Wall

2022/src/Aoc/Day3.hs

@@ -0,0 +1,29 @@
+module Aoc.Day3 (solve, halve, shared, charToInt) where
+
+import Data.Char
+import qualified Data.Set as Set
+import Data.List.Split (chunksOf)
+
+halve :: String -> [String]
+halve xs = [front, back]
+  where
+    midpoint = length xs `div` 2
+
+    front = take midpoint xs
+    back  = drop midpoint xs
+
+shared :: [String] -> String
+shared xs = Set.toList $ foldr1 Set.intersection $ map Set.fromList xs
+
+charToInt :: Char -> Int
+charToInt c
+  | 'a' <= c && c <= 'z' = ord c - ord 'a' + 1
+  | 'A' <= c && c <= 'Z' = ord c - ord 'A' + 27
+  | otherwise            = -1
+
+solve :: Integer -> String -> Integer
+solve 1 input = sum $ map (toInteger . charToInt . head . shared . halve) $ lines input
+
+solve 2 input = sum $ map (toInteger . charToInt . head . shared) $ chunksOf 3 $ lines input
+
+solve _ _ = 0