day 2

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

aoc2024.cabal

@@ -24,3 +24,9 @@ executable p1
   hs-source-dirs: src
   main-is:        P1.hs
   build-depends:  libaoc
+
+executable p2
+  import:         common
+  hs-source-dirs: src
+  main-is:        P2.hs
+  build-depends:  libaoc

src/P2.hs

@@ -0,0 +1,36 @@
+module Main where
+
+import qualified AoC as A (extract)
+import Data.List (inits, tails)
+import Text.Parsec (char, digit, many1, newline, parse, sepBy1, sepEndBy1)
+import Text.Parsec.String (Parser)
+
+parseReports :: Parser [[Int]]
+parseReports =
+  sepEndBy1
+    (sepBy1 (read <$> many1 digit) (char ' '))
+    newline
+
+safe :: [Int] -> Bool
+safe xs =
+  let differences :: [Int]
+      differences = zipWith (-) (tail xs) xs
+   in all (\x -> (x >= 1) && (x <= 3)) differences || all (\x -> (x <= -1) && (x >= -3)) differences
+
+part1 :: [[Int]] -> Int
+part1 = length . filter safe
+
+part2 :: [[Int]] -> Int
+part2 = length . filter dampSafe
+  where
+    dampSafe :: [Int] -> Bool
+    dampSafe xs = any safe (zipWith (++) (inits xs) (tail (tails xs)))
+
+main :: IO ()
+main =
+  do
+    raw <- readFile "./inputs/p2.in"
+    -- parse the input
+    let reports = A.extract $ parse parseReports "" raw
+    putStr "Part 1: " >> print (part1 reports)
+    putStr "Part 2: " >> print (part2 reports)