[haskell] Solve Day 3

answers.nix

@@ -7,4 +7,8 @@
     part1 = "2406";
     part2 = "78375";
   };
+  day3 = {
+    part1 = "531932";
+    part2 = "73646890";
+  };
 }

haskell/aoc2023.cabal

@@ -19,8 +19,10 @@ library
     default-language: GHC2021
     build-depends:    base ^>=4.17.2.0
                     , containers
+                    , fingertree
     exposed-modules:  Day1
                     , Day2
+                    , Day3
 
 executable aoc2023
     import:           warnings

haskell/app/Main.hs

@@ -5,10 +5,12 @@ module Main where
 import Day1 qualified
 import Day2 qualified
 import System.Environment (getArgs)
+import qualified Day3
 
 main :: IO ()
 main = do
   getArgs >>= \case
     ["day1"] -> Day1.run
     ["day2"] -> Day2.run
+    ["day3"] -> Day3.run
     args -> error $ "Invlaid args: " <> show args

haskell/default.nix

@@ -1,11 +1,11 @@
-{ mkDerivation, base, containers, lib }:
+{ mkDerivation, base, containers, fingertree, lib }:
 mkDerivation {
   pname = "aoc2023";
   version = "0.1.0.0";
   src = ./.;
   isLibrary = true;
   isExecutable = true;
-  libraryHaskellDepends = [ base containers ];
+  libraryHaskellDepends = [ base containers fingertree ];
   executableHaskellDepends = [ base ];
   homepage = "https://git.pub.solar/axeman/aoc2023";
   description = "Advent of Code 2023";

haskell/src/Day3.hs

@@ -0,0 +1,85 @@
+module Day3 where
+
+import Data.Char
+import Data.Containers.ListUtils (nubOrd)
+import Data.IntervalMap.FingerTree (Interval (..), IntervalMap)
+import Data.IntervalMap.FingerTree qualified as IntervalMap
+import Data.Map (Map)
+import Data.Map.Lazy qualified as Map
+import Data.Maybe (mapMaybe)
+import Data.Set qualified as Set
+
+run :: IO ()
+run = do
+  (parts, numbers) <- readInput
+  putStrLn $ "Part 1 Answer: " <> show (part1 parts numbers)
+  putStrLn $ "Part 2 Answer: " <> show (part2 parts numbers)
+
+part1 :: PartsMap -> NumbersMap -> Int
+part1 parts numbers = do
+  let partCoords = Map.keysSet parts
+      potentialPartNumberCoords =
+        Set.unions $ Set.map (Set.fromList . neighbours) partCoords
+      partNumberWithCoords =
+        Set.unions $
+          Set.map
+            (\c -> Set.fromList $ IntervalMap.search c numbers)
+            potentialPartNumberCoords
+      partNumbers = map snd $ Set.toList partNumberWithCoords
+  sum partNumbers
+
+neighbours :: Coord -> [Coord]
+neighbours (x, y) =
+  [ (x1, y1)
+    | x1 <- [x - 1 .. x + 1],
+      y1 <- [y - 1 .. y + 1]
+  ]
+
+part2 :: PartsMap -> NumbersMap -> Int
+part2 parts numbers =
+  let starPartCoords = Map.keys $ Map.filter (== '*') parts
+      gearRatios = mapMaybe (gearRatio numbers) starPartCoords
+   in sum gearRatios
+
+gearRatio :: NumbersMap -> Coord -> Maybe Int
+gearRatio numbers gearCoord =
+  let neighbourNums = nubOrd $ concatMap (\c -> nubOrd $ IntervalMap.search c numbers) (neighbours gearCoord)
+   in case neighbourNums of
+        [(_, n1), (_, n2)] -> Just (n1 * n2)
+        _ -> Nothing
+
+type Coord = (Int, Int)
+
+type PartsMap = Map Coord Char
+
+type NumbersMap = IntervalMap Coord Int
+
+readInput :: IO (PartsMap, NumbersMap)
+readInput = do
+  ls <- lines <$> getContents
+  pure $ foldr parseLine (mempty, mempty) $ zip [0 ..] ls
+
+parseLine :: (Int, String) -> (PartsMap, NumbersMap) -> (PartsMap, NumbersMap)
+parseLine (x, line) (accParts, accNumbers) =
+  (parsePartsLine x line accParts, parseNumbersLine x line accNumbers)
+
+parsePartsLine :: Int -> String -> PartsMap -> PartsMap
+parsePartsLine x line acc =
+  let withIndices = zip [0 ..] line
+      parts = filter (\c -> snd c `notElem` "0123456789.\n") withIndices
+      partsWithX = map (\(y, c) -> ((x, y), c)) parts
+   in acc <> Map.fromList partsWithX
+
+parseNumbersLine :: Int -> String -> NumbersMap -> NumbersMap
+parseNumbersLine x = go 0 Nothing
+  where
+    go :: Int -> Maybe (Int, Int) -> [Char] -> NumbersMap -> NumbersMap
+    go _ Nothing [] m = m
+    go curY Nothing (c : rest) m
+      | isDigit c = go (curY + 1) (Just (curY, digitToInt c)) rest m
+      | otherwise = go (curY + 1) Nothing rest m
+    go curY (Just (startY, curNum)) [] m =
+      IntervalMap.insert (Interval (x, startY) (x, curY - 1)) curNum m
+    go curY (Just (startY, curNum)) (c : rest) m
+      | isDigit c = go (curY + 1) (Just (startY, curNum * 10 + digitToInt c)) rest m
+      | otherwise = go (curY + 1) Nothing rest $ IntervalMap.insert (Interval (x, startY) (x, curY - 1)) curNum m

input/day3

@@ -0,0 +1,140 @@
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input/day3-eg

@@ -0,0 +1,10 @@
+467..114..
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