Day 2

Author: Porges

.gitattributes

@@ -0,0 +1 @@
+*.sh eol=lf

2024/README.md

@@ -1,8 +1,15 @@
-# 2024
-
-## Day 1 – Awk
-
-```console
-$ awk -f day01-01.awk < input1
-$ awk -f day01-02.awk < input1
-```
+# 2024
+
+## Day 1 – Awk
+
+```console
+$ awk -f day01-01.awk < input1
+$ awk -f day01-02.awk < input1
+```
+
+## Day 2 – Haskell
+
+```console
+$ runhaskell day02-01.hs < input2
+$ runhaskell day02-02.hs < input2
+```

2024/day02-01.hs

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+isValid :: [Int] -> Bool
+isValid levels = safe levels || safe (reverse levels) 
+    where
+    safe = all (\x -> x >= 1 && x <= 3) . deltas
+    deltas l = zipWith (-) l (tail l)
+
+main = do
+    reports <- map (map read) . map words . lines <$> getContents
+    let validReports = filter isValid reports
+    print (length validReports)

2024/day02-02.hs

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+isValid :: [Int] -> Bool
+isValid levels = safe levels || safe (reverse levels) 
+    where
+    safe = all (\x -> x >= 1 && x <= 3) . deltas
+    deltas l = zipWith (-) l (tail l)
+
+drop1 :: [a] -> [[a]]
+drop1 [] = []
+drop1 (x:xs) = xs : map (x:) (drop1 xs)
+
+main = do
+    reports <- map (map read) . map words . lines <$> getContents
+    let validReports = filter (any isValid . drop1) reports
+    print (length validReports)