Day 4

src/Day4.hs

@@ -0,0 +1,14 @@
+module Day4 (day4) where
+
+import Day4.Part1
+import Day4.Part2
+
+day4 :: IO ()
+day4 = do
+   input <- readFile "ressources/day04-input"
+   putStrLn "Day4"
+   let score1 = countFullyOverlappingPairs input
+   putStrLn ("Number of fully overlapping section pairs " ++ show score1)
+   let score2 = countOverlappingPairs input
+   putStrLn ("Number of section pairs that overlap at all " ++ show score2)
+   return ()

src/Day4/Part1.hs

@@ -0,0 +1,16 @@
+module Day4.Part1 (
+  isFullyOverlapping,
+  countFullyOverlappingPairs
+)
+ where
+   
+import Day4.Shared
+import Data.Ranged
+
+isFullyOverlapping :: ElfPair -> Bool
+isFullyOverlapping (a, b) = a `rangeEncloses` b || b `rangeEncloses` a
+
+countFullyOverlappingPairs :: String -> Int
+countFullyOverlappingPairs input = length $ filter isFullyOverlapping pairs
+  where
+    pairs = map elfPair $ lines input

src/Day4/Part2.hs

@@ -0,0 +1,16 @@
+module Day4.Part2 (
+  countOverlappingPairs
+) where
+
+import Day4.Shared
+import Data.Ranged
+
+
+isOverlapping :: ElfPair -> Bool
+isOverlapping (a, b) = a `rangeOverlap` b || b `rangeOverlap` a
+
+countOverlappingPairs :: String -> Int
+countOverlappingPairs input = length $ filter isOverlapping pairs
+  where
+    pairs = map elfPair $ lines input
+

src/Day4/Shared.hs

@@ -0,0 +1,29 @@
+module Day4.Shared(
+  section,
+  elfPair,
+  (+=+),
+  Section,
+  ElfPair
+) where
+
+
+import Data.Ranged
+import Control.Lens
+
+type Section = Range Int
+type ElfPair = (Section, Section)
+
+(+=+) :: Int -> Int -> Range Int
+x +=+ y = Range (BoundaryBelow x) (BoundaryAbove y)
+
+section :: String -> Section
+section s = read start +=+ read end
+  where
+    (start, rest) = break ('-' ==) s
+    end = drop 1 rest
+
+
+elfPair :: String -> ElfPair
+elfPair s = over each section (first, drop 1 second)
+  where
+    (first, second) = break (',' ==) s

src/Lib.hs

@@ -2,8 +2,8 @@ module Lib
     ( someFunc
     ) where
       
-import Day3      
+import Day4      
 
 someFunc :: IO ()
-someFunc = day3
+someFunc = day4