Day 8 - haskell

README.md

@@ -16,7 +16,8 @@
 - [x] Elixir
   - [Day 5](./day-05)
 - [] Emacs Lisp
-- [] Haskell
+- [x] Haskell
+  - [Day 7](./day-07)
 - [] Java
 - [x] JavaScript
   - [Day 6](./day-06)

day-07/sol.hs

@@ -0,0 +1,117 @@
+import           Data.List    (find, transpose)
+import qualified Data.Set     as Set
+import qualified Data.Text    as Text
+import qualified Data.Text.IO as Text
+
+countVisibleTrees ::
+     [[Int]] -> [Int] -> Int -> (Set.Set (Int, Int)) -> (Set.Set (Int, Int))
+countVisibleTrees [] _ _ seen = seen
+countVisibleTrees (row:rows) maxTrees depth seen =
+  countVisibleTrees
+    rows
+    (zipWith (\x y -> max x y) row maxTrees)
+    (depth + 1)
+    (foldl
+       (\acc x -> Set.insert x acc)
+       seen
+       (zipWith
+          (\i x ->
+             if x == 1
+               then (depth, i)
+               else (0, 0))
+          [0 ..]
+          (zipWith
+             (\x y ->
+                if x > y
+                  then 1
+                  else 0)
+             row
+             maxTrees)))
+
+treeScore :: [[Int]] -> (Int, Int) -> Int -> Int -> [Int]
+treeScore digits (x, y) width height =
+  let currentHeight = ((digits !! y) !! x)
+   in [ (case (find
+                 (\x -> (digits !! y) !! x >= currentHeight)
+                 [(x + 1) .. (width - 1)]) of
+           Just value -> (value - x)
+           Nothing    -> (width - x - 1))
+      , (case (find
+                 (\x -> (digits !! y) !! x >= currentHeight)
+                 (reverse [0 .. (x - 1)])) of
+           Just value -> (x - value)
+           Nothing    -> x)
+      , (case (find
+                 (\y -> (digits !! y) !! x >= currentHeight)
+                 (reverse [0 .. (y - 1)])) of
+           Just value -> (y - value)
+           Nothing    -> y)
+      , (case (find
+                 (\y -> (digits !! y) !! x >= currentHeight)
+                 [(y + 1) .. (height - 1)]) of
+           Just value -> (value - y)
+           Nothing    -> (height - y - 1))
+      ]
+
+getDigitsFromString :: String -> [Int]
+getDigitsFromString = map (read . (: ""))
+
+rotl :: [[Int]] -> [[Int]]
+rotl = reverse . transpose
+
+rotr :: [[Int]] -> [[Int]]
+rotr = transpose . reverse
+
+mmult :: [[Int]] -> [[Int]] -> [[Int]]
+mmult a b = [[sum $ zipWith (*) ar bc | bc <- (transpose b)] | ar <- a]
+
+main = do
+  ls <- fmap Text.lines (Text.readFile "input")
+  let digits = map (getDigitsFromString . Text.unpack) ls
+  let height = length digits
+  let width = length (head digits)
+  let topDownSeen =
+        countVisibleTrees digits (take width (repeat (-1))) 0 Set.empty
+  let rightLeftSeen =
+        Set.map
+          (\x -> ((snd x), width - (fst x) - 1))
+          (countVisibleTrees
+             (rotl digits)
+             (take height (repeat (-1)))
+             0
+             Set.empty)
+  let downTopSeen =
+        Set.map
+          (\x -> (height - (fst x) - 1, (snd x)))
+          (countVisibleTrees
+             (reverse digits)
+             (take width (repeat (-1)))
+             0
+             Set.empty)
+  let leftRightSeen =
+        Set.map
+          (\x -> (height - (snd x) - 1, (fst x)))
+          (countVisibleTrees
+             (rotr digits)
+             (take height (repeat (-1)))
+             0
+             Set.empty)
+  let allSeen =
+        (foldl
+           (\acc x -> Set.union acc x)
+           Set.empty
+           [topDownSeen, rightLeftSeen, downTopSeen, leftRightSeen])
+  print (Set.size allSeen)
+  print
+    (maximum
+       (map
+          (\y ->
+             maximum
+               (map
+                  (\x ->
+                     (foldl
+                        (\acc x -> acc * x)
+                        1
+                        (treeScore digits (x, y) width height)))
+                  [0 .. (width - 1)]))
+          [0 .. (height - 1)]))