tests

.ghcid

@@ -1 +1 @@
---command="cabal repl --repl-options=-fno-break-on-exception --repl-options=-fno-break-on-error --repl-options=-v1 --repl-options=-ferror-spans --repl-options=-j --repl-options=-Wall"
+--command="cabal repl --repl-options=-fno-break-on-exception --repl-options=-fno-break-on-error --repl-options=-v1 --repl-options=-ferror-spans --repl-options=-j"

solutions/src/2023/10.hs

@@ -8,12 +8,47 @@ Maintainer  : emertens@gmail.com
 
 <https://adventofcode.com/2023/day/10>
 
+>>> :{
+:main +
+".F----7F7F7F7F-7....
+.|F--7||||||||FJ....
+.||.FJ||||||||L7....
+FJL7L7LJLJ||LJ.L-7..
+L--J.L7...LJS7F-7L7.
+....F-J..F7FJ|L7L7L7
+....L7.F7||L7|.L7L7|
+.....|FJLJ|FJ|F7|.LJ
+....FJL-7.||.||||...
+....L---J.LJ.LJLJ...
+"
+:}
+70
+8
+
+>>> :{
+:main +
+"FF7FSF7F7F7F7F7F---7
+L|LJ||||||||||||F--J
+FL-7LJLJ||||||LJL-77
+F--JF--7||LJLJ7F7FJ-
+L---JF-JLJ.||-FJLJJ7
+|F|F-JF---7F7-L7L|7|
+|FFJF7L7F-JF7|JL---7
+7-L-JL7||F7|L7F-7F7|
+L.L7LFJ|||||FJL7||LJ
+L7JLJL-JLJLJL--JLJ.L
+"
+:}
+80
+10
+
 -}
 module Main (main) where
 
 import Advent (getInputMap)
-import Advent.Coord (cardinal, invert, invert', south, turnLeft, Coord)
+import Advent.Coord (cardinal, invert, invert', south, north, west, turnRight, Coord)
 import Advent.Search (dfsN, dfsOn)
+import Data.List (nub, (\\))
 import Data.Map (Map)
 import Data.Map qualified as Map
 import Data.Set (Set)
@@ -27,17 +62,25 @@ import Data.Set qualified as Set
 main :: IO ()
 main =
  do input <- getInputMap 2023 10
-    let start = head [k | (k, 'S') <- Map.assocs input]
-    let dir0 = south -- XXX: hardcoded
+    let (start, dir0) = pickStart input
     let route = [(here,dir) | (dir,here) <- dfsOn snd (step input) (dir0, dir0+start)]
 
     let pipe = Set.fromList (map fst route)
     let containable = Map.keysSet input `Set.difference` pipe
     let candidates = Set.fromList (concatMap (rightof input) route) `Set.difference` pipe
-    let contained = Set.fromList (dfsN (openNeighbors containable) (Set.toList candidates))
-    
+    let contained = dfsN (openNeighbors containable) (Set.toList candidates)
+
     print (length route `quot` 2)
-    print (Set.size contained)
+    print (length contained)
+
+pickStart :: Map Coord Char -> (Coord, Coord)
+pickStart input = head $
+  [ (k, dir)
+  | (k, 'S') <- Map.assocs input
+  , (dir, ok) <- [(south, "L|J"), (north, "F|7"), (west,"7-J")]
+  , let next = Map.findWithDefault '.' (k+dir) input
+  , next `elem` ok
+  ]
 
 openNeighbors :: Set Coord -> Coord -> [Coord]
 openNeighbors input x = [y | y <- cardinal x, Set.member y input]
@@ -48,19 +91,15 @@ step inp (dir, here) =
 
 rightof :: Map Coord Char -> (Coord, Coord) -> [Coord]
 rightof input (here, dir) =
-  [ here + d
-  | let pipe = pipeEffect (input Map.! here)
-  , d <- iterate turnLeft (-dir)
-  , then drop 1
-  , then takeWhile by dir /= pipe d]
+  nub [turnRight d + here | d <- [dir, pipeEffect (input Map.! here) dir]]
 
 pipeEffect :: Char -> Coord -> Coord
 pipeEffect = \case
   'S' -> id
   '-' -> id
   '|' -> id
   '7' -> invert
-  'J' -> invert'
   'L' -> invert
+  'J' -> invert'
   'F' -> invert'
   _   -> error "bad pipe character"