1 files changed, 74 insertions, 0 deletions
diff --git a/2023/11-Cosmic_Expansion/first.hs b/2023/11-Cosmic_Expansion/first.hs
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+++ b/2023/11-Cosmic_Expansion/first.hs
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+-- requires cabal install --lib megaparsec parser-combinators
+module Main (main) where
+
+import Control.Applicative.Permutations
+import Control.Monad (void, when)
+import Data.Char qualified as C
+import Data.Either
+import Data.Functor
+import Data.List qualified as L
+import Data.Map qualified as M
+import Data.Maybe
+import Data.Set qualified as S
+import Data.Vector qualified as V
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+
+import Debug.Trace
+
+exampleExpectedOutput = 374
+
+type Position = (Int, Int)
+type Input = [Position]
+
+type Parser = Parsec Void String
+
+parseLine :: Parser Position
+parseLine = do
+  (SourcePos _ y x) <- getSourcePos
+  void $ char '#' <* some (void (char '.') <|> void eol)
+  return (unPos x, unPos y)
+
+parseInput' :: Parser Input
+parseInput' = do
+  some (void (char '.') <|> void eol)
+  some parseLine <* eof
+
+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 = distances $ map expand input
+  where
+    distances :: Input -> Int
+    distances [] = 0
+    distances (x:xs) = distances' x xs + distances xs
+    distances' :: Position -> Input -> Int
+    distances' a [] = 0
+    distances' a (x:xs) = distance a x + distances' a xs
+    distance :: Position -> Position -> Int
+    distance (x1, y1) (x2, y2) = abs (x2-x1) + abs (y2-y1)
+    expand :: Position -> Position
+    expand (x, y) = (x', y')
+      where
+        x' = x + S.size (S.filter (< x) emptyCols)
+        y' = y + S.size (S.filter (< y) emptyRows)
+    cols = S.fromList $ map fst input
+    rows = S.fromList $ map snd input
+    allCols = S.fromList [0..S.findMax cols]
+    allRows = S.fromList [0..S.findMax rows]
+    emptyCols = allCols S.\\ cols
+    emptyRows = allRows S.\\ rows
+
+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