day12: primitive depth first solution

Too slow, unfortunately

2022/day12/day12.hs

@@ -0,0 +1,47 @@
+import Data.List
+import Data.Maybe
+
+type Path = ([String], [(Int, Int)])
+
+main :: IO ()
+main = do
+  input <- lines <$> readFile "testinput"
+  let s = findLetter 'S' input
+  print $ walkTo 'E' (input, []) s
+
+findLetter :: Char -> [String] -> (Int, Int)
+findLetter c = f <*> fromJust . findIndex (/= Nothing) <$> map (elemIndex c)
+  where
+    f x y = (head $ catMaybes x, y)
+
+walkTo :: Char -> Path -> (Int, Int) -> Int
+walkTo c (field, visited) (x, y)
+  | field !! y !! x == c = 0
+  | null newCoords = (maxBound :: Int) `div` 2
+  | otherwise =
+    if length visited > lenX * lenY
+      then (maxBound :: Int) `div` 2
+      else succ $
+           minimum $
+           map (walkTo c (field, (x, y) : visited)) newCoords
+  where
+    lenX = length $ head field
+    lenY = length field
+    char = field !! y !! x
+    current =
+      if char == 'S'
+        then pred 'a'
+        else char
+    newCoords =
+      [ (x + x', y + y')
+      | x' <- [-1 .. 1]
+      , x' + x >= 0
+      , x' + x < lenX
+      , y' <- [-1 .. 1]
+      , y' + y >= 0
+      , y + y' < lenY
+      , abs x' /= abs y'
+      , let a = field !! (y + y') !! (x + x')
+         in (a `elem` ['a' .. succ current] || (a == 'E' && current == 'z'))
+      , (x + x', y + y') `notElem` visited
+      ]