From 7f5f185eacc15623c02e6e06baecad6671780014 Mon Sep 17 00:00:00 2001
From: Neil Smith <NeilNjae@users.noreply.github.com>
Date: Mon, 2 Dec 2024 09:38:35 +0000
Subject: [PATCH] Done day 2

---
 advent02/Main.hs     | 38 ++++++++++++++++++++++++++++++++++++++
 adventofcode24.cabal |  5 +++++
 2 files changed, 43 insertions(+)
 create mode 100644 advent02/Main.hs

diff --git a/advent02/Main.hs b/advent02/Main.hs
new file mode 100644
index 0000000..a0f4534
--- /dev/null
+++ b/advent02/Main.hs
@@ -0,0 +1,38 @@
+-- Writeup at https://work.njae.me.uk/2024/12/02/advent-of-code-2024-day-2/
+
+import AoC
+import Data.List
+
+main :: IO ()
+main = 
+  do  dataFileName <- getDataFileName
+      text <- readFile dataFileName
+      let reports = fmap readLine $ lines text
+      print $ part1 reports
+      print $ part2 reports
+
+part1, part2 :: [[Int]] -> Int
+part1 reports = length $ filter isSafe reports
+part2 reports = length $ filter isSafe' reports
+    where isSafe' l = isSafe l || safeWhenDamped l
+
+isSafe, allSameSign, bigEnough, smallEnough, safeWhenDamped :: [Int] -> Bool
+isSafe xs = allSameSign diffs && bigEnough diffs && smallEnough diffs
+  where diffs = zipWith (-) xs (tail xs)
+
+allSameSign xs 
+ | all (>0) xs = True
+ | all (<0) xs = True
+ | otherwise = False
+
+bigEnough = all ((>= 1) . abs)
+smallEnough = all ((<= 3) . abs)
+
+safeWhenDamped = (any isSafe) . damped
+
+damped :: [Int] -> [[Int]]
+damped line = zipWith (++) (inits line) (drop 1 $ tails line)
+
+readLine :: String -> [Int]
+readLine = (fmap read) . words
+
diff --git a/adventofcode24.cabal b/adventofcode24.cabal
index f922676..565d1d9 100644
--- a/adventofcode24.cabal
+++ b/adventofcode24.cabal
@@ -76,3 +76,8 @@ executable advent01
   import: warnings, common-extensions, build-directives, common-modules
   main-is: advent01/Main.hs
   build-depends: multiset
+
+executable advent02
+  import: warnings, common-extensions, build-directives, common-modules
+  main-is: advent02/Main.hs
+  
\ No newline at end of file
-- 
2.34.1