Day 22, part a

src/AOC-22a.hs

 module Main where
 
+import Data.Char ( isDigit )
+import Data.Functor ( void, ($>) )
+import Data.Ix ( Ix(range) )
+import qualified Data.Set as S
+import Data.Set (Set)
+import Text.ParserCombinators.ReadP
+    ( ReadP, (<++), char, munch1, option, readP_to_S, string )
+
+type Range =(Int,Int)
+data Instruction 
+  = On Range Range Range
+  | Off Range Range Range
+  deriving Show
+
+type Point = (Int,Int,Int)
+
+parseInt :: ReadP Int
+parseInt = do
+  sn <- option 1 (char '-' $> (-1)) 
+  digits <- read <$> munch1 isDigit
+  pure $ sn * digits
+
+parseRange :: ReadP Range
+parseRange = do
+  mn <- parseInt
+  void $ string ".."
+  mx <- parseInt
+  pure $ (mn,mx)
+
+parseInstruction :: ReadP Instruction
+parseInstruction = do
+  op <- (string "on" $> On) <++ (string "off" $> Off)
+  void $ string " x="
+  xr <- parseRange
+  void $ string ",y="
+  yr <- parseRange
+  void $ string ",z="
+  zr <- parseRange
+  pure $ op xr yr zr
+
+instance Read Instruction where
+  readsPrec _ = readP_to_S parseInstruction
+
+intersectRange :: Range -> Range -> Range
+intersectRange (aMin,aMax) (bMin,bMax) = (max aMin bMin, min aMax bMax)
+
+interpret :: [Instruction] -> Set Point
+interpret = foldl oneInstruction S.empty where
+  oneInstruction s (On xr yr zr) = s `S.union` pts xr yr zr 
+  oneInstruction s (Off xr yr zr) = s `S.difference` pts xr yr zr
+  pts xr yr zr = S.fromList $ range ((xMin,yMin,zMin),(xMax,yMax,zMax)) where
+    constrain r = r `intersectRange` (-50,50)
+    (xMin,xMax) = constrain xr
+    (yMin,yMax) = constrain yr
+    (zMin,zMax) = constrain zr
+
 main :: IO ()
-main = pure ()
+main = do
+  instrs <- map (read @Instruction) . lines <$> readFile "data/reactor.txt"
+  print . S.size . interpret $ instrs

test/reactor.txt

+on x=-20..26,y=-36..17,z=-47..7
+on x=-20..33,y=-21..23,z=-26..28
+on x=-22..28,y=-29..23,z=-38..16
+on x=-46..7,y=-6..46,z=-50..-1
+on x=-49..1,y=-3..46,z=-24..28
+on x=2..47,y=-22..22,z=-23..27
+on x=-27..23,y=-28..26,z=-21..29
+on x=-39..5,y=-6..47,z=-3..44
+on x=-30..21,y=-8..43,z=-13..34
+on x=-22..26,y=-27..20,z=-29..19
+off x=-48..-32,y=26..41,z=-47..-37
+on x=-12..35,y=6..50,z=-50..-2
+off x=-48..-32,y=-32..-16,z=-15..-5
+on x=-18..26,y=-33..15,z=-7..46
+off x=-40..-22,y=-38..-28,z=23..41
+on x=-16..35,y=-41..10,z=-47..6
+off x=-32..-23,y=11..30,z=-14..3
+on x=-49..-5,y=-3..45,z=-29..18
+off x=18..30,y=-20..-8,z=-3..13
+on x=-41..9,y=-7..43,z=-33..15
+on x=-54112..-39298,y=-85059..-49293,z=-27449..7877
+on x=967..23432,y=45373..81175,z=27513..53682
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