Both stars of Day 4!

2022/aoc2022.cabal

@@ -32,4 +32,4 @@ executable aoc2022
     build-depends:    base ^>=4.16.3.0, split ^>=0.2.3.5
     hs-source-dirs:   app
     default-language: Haskell2010
-    other-modules:    Day1.Main Day2.Main Day3.Main
+    other-modules:    Day1.Main Day2.Main Day3.Main Day4.Main

2022/app/Day4/Main.hs

@@ -0,0 +1,47 @@
+module Day4.Main where
+
+import System.IO
+import Data.List.Split
+
+main :: IO ()
+main = do
+    putStrLn "Day 4"
+    
+    handle <- openFile "app/Day4/input" ReadMode
+    contents <- hGetContents handle
+
+    let r1 = part1 contents
+    putStrLn $ "part 1: " ++ show r1
+
+    let r2 = part2 contents
+    putStrLn $ "part 2: " ++ show r2
+
+listToPair :: [a] -> (a, a)
+listToPair l = (l !! 0, l !! 1)
+
+type Start = Int
+type End = Int
+type Section = (Start, End)
+
+parseData :: String -> [(Section, Section)]
+parseData contents = transformOuter
+    where
+        pairs = map (splitOn ",") (lines contents)
+        ranges = (map . map) (splitOn "-") pairs
+        toNumbers = (map . map . map) (read :: String -> Int) ranges
+        transformInner = (map . map) listToPair toNumbers
+        transformOuter = map listToPair transformInner
+        
+
+contained :: Section -> Section -> Bool
+contained (as, ae) (bs, be) = as <= bs && ae >= be || bs <= as && be >= ae
+
+overlap :: Section -> Section -> Bool
+overlap (as, ae) (bs, be) = bs <= as && be >= as ||
+                            bs <= ae && be >= ae ||
+                            as <= bs && ae >= bs ||
+                            as <= be && ae >= be
+
+part1, part2 :: String -> Int
+part1 contents = length $ filter (uncurry contained) $ parseData contents
+part2 contents = length $ filter (uncurry overlap)   $ parseData contents

2022/app/Main.hs

@@ -3,9 +3,11 @@ module Main where
 import qualified Day1.Main as Day1
 import qualified Day2.Main as Day2
 import qualified Day3.Main as Day3
+import qualified Day4.Main as Day4
 
 main :: IO ()
 main = do
     Day1.main
     Day2.main
     Day3.main
+    Day4.main