Day 15

src/AOC-15a.hs

 module Main where
 
+import Control.Monad
+import Data.Array
+import qualified Data.Map as M
+import Data.Map (Map)
+
+type Position = (Int,Int)
+type ChitonMap = Array Position Int
+
+readMap :: String -> ChitonMap
+readMap s = arr where
+  ps = do
+    (rx,row) <- enumerate . lines $ s
+    (cx,col) <- enumerate row
+    pure $ ((rx,cx),read @Int [col])
+  enumerate = zip @Int [0..]
+  maxX = maximum . (map (fst . fst)) $ ps
+  maxY = maximum . (map (snd . fst)) $ ps
+  arr = array ((0,0),(maxX,maxY)) ps
+
+showMap :: ChitonMap -> String
+showMap cm = unlines [ [head . show $ (cm ! (x,y)) | y <- [0..maxY]] | x <- [0..maxX]] where
+  ((0,0),(maxX,maxY)) = bounds cm
+
+neighbors :: Array Position a -> Position -> [Position]
+neighbors cm (x,y) = do
+  p <- [(x-1,y),(x,y-1),(x,y+1),(x+1,y)]
+  guard . inRange (bounds cm) $ p
+  pure p
+
+search :: ChitonMap -> Position -> Position -> (Int,[Position])
+search cm start end = iter (M.singleton start (0,[start])) where
+  iter :: Map Position (Int,[Position]) -> (Int,[Position])
+  iter costmap 
+    | costmap == newCostmap = costmap M.! end -- this gives a reversed path
+    | otherwise = iter newCostmap
+    where
+      newCostmap = M.unionWith min costmap newpaths
+      newpaths = M.unionsWith min $ do
+        (pos,(cost,path)) <- M.assocs costmap
+        n <- neighbors cm pos
+        pure $ M.singleton n (cost + cm ! n, n : path)
+
+maxPoint :: Array Position a -> Position
+maxPoint = snd . bounds 
+
 main :: IO ()
-main = pure ()
+main = do
+  cm <- readMap <$> readFile "data/chitons.txt"
+  let (cost,_) = search cm (0,0) (maxPoint cm)
+  print cost

src/AOC-15b.hs

 module Main where
 
+import Control.Monad
+import Data.Array
+import qualified Data.Map as M
+import Data.Map (Map)
+
+type Position = (Int,Int)
+type ChitonMap = Array Position Int
+
+readMap :: String -> ChitonMap
+readMap s = arr where
+  ps = do
+    (rx,row) <- enumerate . lines $ s
+    (cx,col) <- enumerate row
+    pure $ ((rx,cx),read @Int [col])
+  enumerate = zip @Int [1..]
+  maxX = maximum . (map (fst . fst)) $ ps
+  maxY = maximum . (map (snd . fst)) $ ps
+  arr = array ((1,1),(maxX,maxY)) ps
+
+
+extendMap :: ChitonMap -> ChitonMap
+extendMap cm = result where
+  result = array newbounds [(p,valueAt p) | p <- range newbounds]
+  ((1,1),(xMax,yMax)) = bounds cm
+  newbounds = ((1,1),(5*xMax,5*yMax))
+  valueAt (x,y)
+    | x > xMax = shift $ valueAt (x-xMax,y)
+    | y > yMax = shift $ valueAt (x,y-yMax)
+    | otherwise = cm ! (x,y)
+  shift 9 = 1
+  shift v = v+1
+
+showMap :: ChitonMap -> String
+showMap cm = unlines [ [head . show $ (cm ! (x,y)) | y <- [1..maxY]] | x <- [1..maxX]] where
+  ((1,1),(maxX,maxY)) = bounds cm
+
+neighbors :: Array Position a -> Position -> [Position]
+neighbors cm (x,y) = do
+  p <- [(x-1,y),(x,y-1),(x,y+1),(x+1,y)]
+  guard . inRange (bounds cm) $ p
+  pure p
+
+search :: ChitonMap -> Position -> Position -> Int
+search cm start end = iter 0 (M.singleton start (0,0)) where
+  iter :: Int -> Map Position (Int,Int) -> Int
+  iter step costmap 
+    | M.null newpaths = fst (costmap M.! end)-- this gives a reversed path
+    | otherwise = iter (step+1) newCostmap
+    where
+      newCostmap :: Map Position (Int,Int)
+      newCostmap = M.unionWith min costmap newpaths
+      newpaths = M.unionsWith min $ do
+        (pos,(cost,s)) <- M.assocs costmap
+        guard $ s == step
+        n <- neighbors cm pos
+        pure $ M.singleton n (cost + cm ! n, step+1)
+
+maxPoint :: Array Position a -> Position
+maxPoint = snd . bounds 
+
 main :: IO ()
-main = pure ()
+main = do
+  cm <- extendMap . readMap <$> readFile "data/chitons.txt"
+  let (mn,mx) = bounds cm
+  print $ search cm mn mx

test/chitons.txt

+1163751742
+1381373672
+2136511328
+3694931569
+7463417111
+1319128137
+1359912421
+3125421639
+1293138521
+2311944581
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