X-Git-Url: https://git.njae.me.uk/?a=blobdiff_plain;f=advent18.hs;fp=advent18.hs;h=04ab345e5522feb8001434ab9174c3cffdc8e693;hb=6c33fcf371ca6d7c86e6cb79cc7de5d8af41181b;hp=0000000000000000000000000000000000000000;hpb=89d895a08ce6055bba3649f3178e76c3e5170ae3;p=advent-of-code-16.git

diff --git a/advent18.hs b/advent18.hs
new file mode 100644
index 0000000..04ab345
--- /dev/null
+++ b/advent18.hs
@@ -0,0 +1,42 @@
+import Data.List (iterate, tails)
+
+-- input = "..^^."
+-- input = ".^^.^.^^^^"
+input = "^.^^^.^..^....^^....^^^^.^^.^...^^.^.^^.^^.^^..^.^...^.^..^.^^.^..^.....^^^.^.^^^..^^...^^^...^...^."
+
+
+main :: IO ()
+main = do 
+        part1 
+        part2
+
+
+part1 :: IO ()
+-- part1 = putStrLn $ unlines $ map (showRow) $ take 10 $ iterate nextRow $ readRow input
+part1 = print $ length $ filter (not) $ concat $ take 40 $ iterate nextRow $ readRow input
+
+part2 :: IO ()
+part2 = print $ length $ filter (not) $ concat $ take 400000 $ iterate nextRow $ readRow input
+
+readRow :: String -> [Bool]
+readRow = map (=='^')
+
+showRow :: [Bool] -> String
+showRow = map (\c -> if c then '^' else '.')
+
+extended :: [Bool] -> [Bool]
+extended row = [False] ++ row ++ [False]
+
+nextRow :: [Bool] -> [Bool]
+nextRow = map (isTrap) . segments . extended
+
+segments :: [a] -> [[a]]
+segments = filter ((==3) . length) . map (take 3) . tails
+
+isTrap :: [Bool] -> Bool
+isTrap segment
+    | segment == [True, True, False] = True
+    | segment == [False, True, True] = True
+    | segment == [True, False, False] = True
+    | segment == [False, False, True] = True
+    | otherwise = False