1 files changed, 25 insertions, 0 deletions
diff --git a/2020/3.hs b/2020/3.hs
new file mode 100644
index 0000000..20fe0ec
--- /dev/null
+++ b/2020/3.hs
@@ -0,0 +1,25 @@
+module Main where
+
+import qualified Data.Array as A
+
+import Input
+
+
+main :: IO ()
+main = do
+    input <- getInput 3
+    let height = length input
+        width = length (head input)
+
+    let grid = A.array ((0, 0), (height - 1, width - 1))
+                    [((y, x), fromEnum (c == '#'))
+                    | (y, row) <- zip [0..] input
+                    , (x, c) <- zip [0..] row]
+
+        countSlope hor ver =
+            let nsteps = height `div` ver
+            in sum [grid A.! (ver * i, hor * i `mod` width) | i <- [0..nsteps-1]]
+
+    print (countSlope 3 1)
+
+    print (product (map (uncurry countSlope) [(1,1), (3,1), (5,1), (7,1), (1,2)]))