opqdonut
diff --git a/‎Day21.hs
+54 b/‎Day21.hs
+54
@@ -0,0 +1,54 @@
+module Day21 where
+
+import Data.List
+import Data.Maybe
+import Data.Ord
+
+input = ["083A", "935A", "964A", "149A", "789A"]
+example = ["029A", "980A", "179A", "456A", "379A"]
+
+type Pad = [(Char,(Int,Int))]
+
+pad :: [String] -> Pad
+pad ls = [(c,(x,y)) | (y,l) <- zip [0..] ls
+                    , (x,c) <- zip [0..] l]
+
+numpad = pad ["789"
+             ,"456"
+             ,"123"
+             ," 0A"]
+
+arrowpad = pad [" ^A"
+               ,"<v>"]
+
+paths :: Pad -> Char -> Char -> [[Char]]
+paths p from to
+  | fromX == badX && toY == badY = [hori ++ vert ++ "A"]
+  | fromY == badY && toX == badX = [vert ++ hori ++ "A"]
+  | otherwise = nub [hori ++ vert ++ "A", vert ++ hori ++ "A"]
+  where Just (badX,badY) = lookup ' ' p
+        Just (fromX,fromY) = lookup from p
+        Just (toX,toY) = lookup to p
+        dX = toX-fromX
+        vert = replicate (abs dY) (if dY < 0 then '^' else 'v')
+        hori = replicate (abs dX) (if dX<0 then '<' else '>')
+
+pathsFor :: Pad -> [Char] -> [[Char]]
+pathsFor p s = map concat $ sequence [paths p a b | (a:b:_) <- tails ('A':s)]
+
+unlookup v kvs = lookup v (map (\(a,b)->(b,a)) kvs)
+
+unbuttonsFor p ks = go (fromJust $ lookup 'A' p) ks
+  where go (x,y) ('<':ks) = go (x-1,y) ks
+        go (x,y) ('>':ks) = go (x+1,y) ks
+        go (x,y) ('v':ks) = go (x,y+1) ks
+        go (x,y) ('^':ks) = go (x,y-1) ks
+        go (x,y) ('A':ks) = fromJust (unlookup (x,y) p) : go (x,y) ks
+        go _ [] = []
+
+pathsFull code = concatMap (pathsFor arrowpad) . concatMap (pathsFor arrowpad) $ pathsFor numpad code
+
+bestPath = minimumBy (comparing length) . pathsFull
+
+part1 inp = sum [length (bestPath code) * read (init code) | code <- inp]