Day 12

aoc2022.cabal

       Day10
       Day11
       Day11.Parser
+      Day12
       Day2
       Day2.Part1
       Day2.Part2
     , hspec
     , hspec-megaparsec
     , lens
+    , linear
     , matrix
     , megaparsec
     , mtl
     , parsec
+    , search-algorithms
     , sort
     , split
     , text
     , hspec
     , hspec-megaparsec
     , lens
+    , linear
     , matrix
     , megaparsec
     , mtl
     , parsec
+    , search-algorithms
     , sort
     , split
     , text
   other-modules:
       Day10Spec
       Day11Spec
+      Day12Spec
       Day1Spec
       Day2Spec
       Day3Spec
     , hspec
     , hspec-megaparsec
     , lens
+    , linear
     , matrix
     , megaparsec
     , mtl
     , parsec
+    , search-algorithms
     , sort
     , split
     , text

package.yaml

 - hspec-megaparsec
 - mtl
 - sort
+- search-algorithms
+- linear
 
 ghc-options:
 - -Wall

ressources/day12-input

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src/Day12.hs

+module Day12
+  ( day12,
+    possibleStarts,
+    parseGrid,
+    findPath,
+    GridPoints (..),
+    Grid,
+    findBestPath
+  )
+where
+
+import Algorithm.Search (dijkstra)
+import Data.Char (ord)
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.Maybe (mapMaybe)
+import Data.Tuple (swap)
+import Linear.V2 (V2 (..))
+import Data.Sort (sortOn)
+
+type Pos = V2 Int
+
+type Grid = Map Pos Char
+
+data GridPoints = GridPoints { _start :: Pos, _end :: Pos }
+  deriving (Show, Eq)
+
+parseGrid :: String -> (GridPoints, Grid)
+parseGrid input =
+  ( GridPoints
+      { _start = inverseGrid Map.! 'S',
+        _end = inverseGrid Map.! 'E'
+      },
+    Map.fromList grid
+  )
+  where
+    rows = zip [0 ..] $ lines input
+    grid = concatMap (uncurry colsForRow) rows
+    inverseGrid = Map.fromList $ map swap grid
+
+colsForRow :: Int -> String -> [(Pos, Char)]
+colsForRow r = zipWith makePos [0 ..]
+  where
+    makePos c height = (V2 r c, height)
+
+findPath :: Grid -> GridPoints -> Maybe (Int, [Pos])
+findPath grid GridPoints {_start = start, _end = end} =
+  dijkstra (neighbors grid) (const . const 1) solutionFound start
+  where
+    solutionFound = (==) end
+
+neighbors :: Grid -> Pos -> [Pos]
+neighbors grid pos = filter (canMove grid pos) possiblePositions
+  where
+    directions = [V2 1 0, V2 (-1) 0, V2 0 1, V2 0 (-1)]
+    possiblePositions = map (+ pos) directions
+
+canMove :: Grid -> Pos -> Pos -> Bool
+canMove grid from p = case grid Map.!? p of
+  Just c -> asHeight c <= (currentHeight + 1)
+  Nothing -> False
+  where
+    asHeight 'S' = asHeight 'a'
+    asHeight 'E' = asHeight 'z'
+    asHeight x = ord x - ord 'a'
+    currentHeight = asHeight $ grid Map.! from
+
+possibleStarts :: Grid -> [Pos]
+possibleStarts grid = map fst $ filter (\(_, v) -> v == 'a') (Map.toList grid)
+
+findBestPath :: Grid -> GridPoints -> (Int, [Pos])
+findBestPath grid points = fastest
+  where
+    starts = possibleStarts grid
+    newPoints = [points { _start = s} | s <- starts]
+    allPaths = mapMaybe (findPath grid) newPoints
+    fastest = head $ sortOn fst allPaths
+
+day12 :: IO ()
+day12 = do
+  input <- readFile "ressources/day12-input"
+  putStrLn "Day12"
+  let (positions, grid) = parseGrid input
+  let path = findPath grid positions
+  putStrLn ("Cost and path : " ++ show path)
+  let fastest = findBestPath grid positions
+  putStrLn ("Cost and path for nices route: " ++ show fastest)

src/Lib.hs

 import Day9 (day9)
 import Day10 (day10)
 import Day11 (day11)
+import Day12 (day12)
 
 days :: [IO ()]
-days = [day1, day2, day3, day4, day5, day6, day7, day8, day9, day10, day11]
+days = [day1, day2, day3, day4, day5, day6, day7, day8, day9, day10, day11, day12]
 
 sep :: IO ()
 sep = putStrLn "---------"

test/Day12Spec.hs

+{-# LANGUAGE QuasiQuotes #-}
+
+module Day12Spec (spec) where
+
+import Day12
+import Test.Hspec
+import Text.Heredoc
+import Data.Maybe (fromJust, isJust)
+
+testInput :: String
+testInput = [str|Sabqponm
+                |abcryxxl
+                |accszExk
+                |acctuvwj
+                |abdefghi
+                |]
+
+spec :: Spec
+spec =
+  describe "Day12" $ do
+    describe "Part1" $ do
+      it "finds a path" $ do
+        let (points, grid) = parseGrid testInput
+        let result = findPath grid points
+        isJust result `shouldBe` True
+        fst (fromJust result) `shouldBe` 31
+      it "finds shortest paths from all lowest points" $ do
+        let (points, grid) = parseGrid testInput
+        let fastest = findBestPath grid points
+        fst fastest `shouldBe` 29