Done day 3

[advent-of-code-20.git] / advent03 / src / advent03.hs

diff --git a/advent03/src/advent03.hs b/advent03/src/advent03.hs
new file mode 100644 (file)
index 0000000..777cf7e
--- /dev/null
+++ b/advent03/src/advent03.hs
@@ -0,0 +1,46 @@
+-- import Debug.Trace
+
+import qualified Data.Set as S
+
+type Position = (Int, Int)
+type Trees = S.Set Position
+
+main :: IO ()
+main = 
+  do  text <- readFile "data/advent03.txt"
+      let (trees, maxCorner) = readGrid text
+      -- print $ S.size trees
+      -- print trees
+      -- print $ maxCorner
+      -- print $ take 25 $ visitedPlaces (1, 3) maxCorner
+      -- print $ takeWhile (withinTrees maxCorner) $ visitedPlaces (1, 3) maxCorner
+      print $ part1 trees maxCorner
+      print $ part2 trees maxCorner
+
+
+readGrid :: String -> (Trees, Position)
+readGrid input = ( S.fromList [ (r, c) 
+                              | r <- [0..maxR], c <- [0..maxC]
+                              , (grid!!r)!!c == '#']
+                 , (maxR, maxC)
+                 )
+    where grid = lines input
+          maxC = (length $ head grid) - 1
+          maxR = (length grid) - 1
+
+
+part1 trees maxCorner = countEncounteredTrees trees maxCorner (1, 3)
+
+part2 trees maxCorner = foldr1 (*) $ map cet [(1, 1), (1, 3), (1, 5), (1, 7), (2, 1)]
+  where cet = countEncounteredTrees trees maxCorner
+
+countEncounteredTrees trees maxCorner delta = S.size $ S.intersection trees visited
+  where visited = S.fromList $ takeWhile (withinTrees maxCorner) $ visitedPlaces delta maxCorner
+
+
+visitedPlaces :: Position -> Position -> [Position]
+visitedPlaces (dr, dc) (_maxR, maxC) = iterate wrappingStep (0, 0)
+  where wrappingStep (r, c) = (r + dr, (c + dc) `mod` (maxC + 1))
+
+withinTrees (maxR, maxC) (r, c) = r >= 0 && r <= maxR && c >= 0 && c <= maxC
+