2024-10 in haskell

2024/10-Hoof_It/example

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+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732

2024/10-Hoof_It/first.hs

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+-- requires cabal install --lib megaparsec parser-combinators heap vector
+module Main (main) where
+
+import           Control.Monad        (void, when)
+import qualified Data.Set             as S
+import qualified Data.Vector          as V
+import qualified Data.Vector.Unboxed  as VU
+import           Data.Void            (Void)
+import           Text.Megaparsec
+import           Text.Megaparsec.Char
+
+exampleExpectedOutput = 36
+
+type Line = VU.Vector Int
+type Input = V.Vector Line
+
+type Parser = Parsec Void String
+
+parseNumber :: Parser Int
+parseNumber = read . pure <$> digitChar
+
+parseLine :: Parser Line
+parseLine = do
+  line <- some parseNumber <* eol
+  return $ VU.generate (length line) (line !!)
+
+parseInput' :: Parser Input
+parseInput' = do
+  line <- some parseLine <* eof
+  return $ V.generate (length line) (line !!)
+
+parseInput :: String -> IO Input
+parseInput filename = do
+  input <- readFile filename
+  case runParser parseInput' filename input of
+    Left bundle  -> error $ errorBundlePretty bundle
+    Right input' -> return input'
+
+compute :: Input -> Int
+compute input = sum $ V.imap scoreLine input
+  where
+    scoreLine :: Int -> VU.Vector Int -> Int
+    scoreLine y line = VU.sum $ VU.imap (\x c -> score x y c) line
+    score :: Int -> Int -> Int -> Int
+    score x y c | c == 0 = S.size $ reachableSummits 0 (x, y)
+                | otherwise = 0
+    reachableSummits :: Int -> (Int, Int) -> S.Set (Int, Int)
+    reachableSummits h (x, y) | h == 9 = S.singleton (x, y)
+                              | otherwise = S.unions $ map (reachableSummits (h+1)) succ
+      where
+        succ = filter valid [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]
+        valid (x, y) = case input V.!? y of
+          Just line -> case line VU.!? x of
+            Just h' -> h+1 == h'
+            _       -> False
+          _ -> False
+
+main :: IO ()
+main = do
+  example <- parseInput "example"
+  let exampleOutput = compute example
+  when  (exampleOutput /= exampleExpectedOutput)  (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute input

2024/10-Hoof_It/input

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+1098921121187650126589432104301010017898
+2347810030090543237676546765218921326323
+3256723345121789078545345896237635495410
+0189654656230650129454210910146546786898
+1018706787649843212323407893056544576781
+0123215498556764501012216324567033675410
+1054912389440189650983345413498122189323
+2367804322339218761874214102439232075014
+3494565011878307010965302101521001456985
+4583876910965498123434456517617652327876
+9672978894328767894525467898908543410434
+8701569765419456987616321010119654306523
+7616054100300345865407890121236701217810
+4567123231201210870301456290547896332912
+3258834998303456961210387787678987441003
+4109985867214327898341295689432196556764
+3457876754321016987654254776501001105895
+2568965698130123216510163897567232234996
+1077654147010154105425672198498143497887
+2089503056923269012334789010398056786546
+1123412147874678901109011001267049805430
+0109892130965165210278921123452121012321
+1236783021089014321367630038983430328901
+0345634569870156752456541127604589437610
+1267825478763247843898430934510678576523
+3216910089654130956707321874321987689430
+4505432198703021013210012365899654238321
+3699801789012982787309898456718723148980
+2789789678101276896456721032100210057671
+1008650521010345785454434549321321060362
+2210541430121289890365410678732639871250
+4341232510537656701274320521548747898341
+1056341423498545432789201230699656743432
+2967650345567230101687112345788745234569
+3878981236750121211096001296787230199678
+4589870109889032349125410187590123288767
+5679665010976541498934231095691054177678
+3038754129889650587432145654782567065549
+2125603236778765676501098723123478450030
+3034512345654656565410181010010989321121

2024/10-Hoof_It/second.hs

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+-- requires cabal install --lib megaparsec parser-combinators heap vector
+module Main (main) where
+
+import           Control.Monad        (void, when)
+import qualified Data.Vector          as V
+import qualified Data.Vector.Unboxed  as VU
+import           Data.Void            (Void)
+import           Text.Megaparsec
+import           Text.Megaparsec.Char
+
+exampleExpectedOutput = 81
+
+type Line = VU.Vector Int
+type Input = V.Vector Line
+
+type Parser = Parsec Void String
+
+parseNumber :: Parser Int
+parseNumber = read . pure <$> digitChar
+
+parseLine :: Parser Line
+parseLine = do
+  line <- some parseNumber <* eol
+  return $ VU.generate (length line) (line !!)
+
+parseInput' :: Parser Input
+parseInput' = do
+  line <- some parseLine <* eof
+  return $ V.generate (length line) (line !!)
+
+parseInput :: String -> IO Input
+parseInput filename = do
+  input <- readFile filename
+  case runParser parseInput' filename input of
+    Left bundle  -> error $ errorBundlePretty bundle
+    Right input' -> return input'
+
+compute :: Input -> Int
+compute input = sum $ V.imap scoreLine input
+  where
+    scoreLine :: Int -> VU.Vector Int -> Int
+    scoreLine y line = VU.sum $ VU.imap (\x c -> score x y c) line
+    score :: Int -> Int -> Int -> Int
+    score x y c | c == 0 = length $ reachableSummits 0 (x, y)
+                | otherwise = 0
+    reachableSummits :: Int -> (Int, Int) -> [(Int, Int)]
+    reachableSummits h (x, y) | h == 9 = [(x, y)]
+                              | otherwise = concatMap (reachableSummits (h+1)) succ
+      where
+        succ = filter valid [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]
+        valid (x, y) = case input V.!? y of
+          Just line -> case line VU.!? x of
+            Just h' -> h+1 == h'
+            _       -> False
+          _ -> False
+
+main :: IO ()
+main = do
+  example <- parseInput "example"
+  let exampleOutput = compute example
+  when  (exampleOutput /= exampleExpectedOutput)  (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute input