1 files changed, 80 insertions, 0 deletions
diff --git a/day10/day10.hs b/day10/day10.hs
new file mode 100644
index 0000000..5c970e5
--- /dev/null
+++ b/day10/day10.hs
@@ -0,0 +1,80 @@
+import Data.Char
+import Data.List
+import Data.Maybe
+
+type Height = Int
+type Coo = (Int, Int)
+type Map = [[Height]]
+
+data Trail = Point Coo Height Trail | Nowhere deriving Show
+
+(!?) :: [[a]] -> Coo -> Maybe a
+mp !? (row, col)
+  | row < 0                   = Nothing
+  | row >= length mp          = Nothing
+  | col < 0                   = Nothing
+  | col >= (length $ head mp) = Nothing
+  | otherwise                 = Just (mp !! row !! col)
+
+consume :: [Char] -> Map
+consume file =
+  map (map (digitToInt)) $ lines file
+
+trailheads2 :: [Coo] -> Int -> Int -> [Height] -> [Coo]
+trailheads2 acc _ _ [] =
+  reverse acc
+trailheads2 acc r c (h:rest)
+  | h == 0 = trailheads2 ((r, c):acc) r (c + 1) rest
+  | otherwise = trailheads2 acc r (c + 1) rest
+
+trailheads1 :: [Coo] -> Int -> Map -> [Coo]
+trailheads1 acc _ [] =
+  acc
+trailheads1 acc r (row:rest) =
+  trailheads1 (acc ++ heads) (r + 1) rest
+  where heads = trailheads2 [] r 0 row
+
+trailheads :: Map -> [Coo]
+trailheads = trailheads1 [] 0
+
+trails2 :: Map -> Trail -> [Trail]
+trails2 mp p@(Point (r,c) h _) =
+  map pointify $
+    catMaybes $
+    map oneup
+    [nxt (-1, 0), nxt (0, -1), nxt (0, 1), nxt (1, 0)]
+  where
+    pointify c = Point c (h+1) p
+    oneup (nr, nc, Just nh) = if nh == h + 1 then Just (nr, nc) else Nothing
+    oneup (_, _, Nothing) = Nothing
+    nxt (dr, dc) = (r+dr, c+dc, mp !? (r+dr, c+dc))
+
+trails1 :: Map -> [Trail] -> [Trail] -> [Trail]
+trails1 _ acc@((Point _ 9 _):_) [] =
+  acc
+trails1 mp acc [] =
+  trails1 mp [] acc
+trails1 mp acc (th@(Point _ 9 _):rest) =
+  trails1 mp (th:acc) rest
+trails1 mp acc (th:rest) =
+  trails1 mp (acc ++ trails2 mp th) rest
+
+trails :: Map -> Coo -> [Trail]
+trails mp th =
+  trails1 mp [] [Point th 0 Nowhere]
+
+score :: [Trail] -> Int
+score th =
+  length $ nub $ map untrail th
+  where
+    untrail (Point c _ _) = c
+
+part1 :: Map -> Int
+part1 mp =
+  sum $ map (score . (trails mp)) $ trailheads mp
+
+main = do
+  file <- readFile "day10.input"
+  let mp = consume file
+  putStrLn ("Part 1: " ++ (show $ part1 mp))
+  --putStrLn ("Part 2: " ++ (show $ part2 mp))