From 5eb58ad076f2cd435b11b140820da224b60b73d5 Mon Sep 17 00:00:00 2001
From: Aria <me@aria.rip>
Date: Mon, 2 Jan 2023 21:58:56 +0000
Subject: initial commit

---
 2020/03b.hs | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 2020/03b.hs

(limited to '2020/03b.hs')

diff --git a/2020/03b.hs b/2020/03b.hs
new file mode 100644
index 0000000..43e7ba2
--- /dev/null
+++ b/2020/03b.hs
@@ -0,0 +1,48 @@
+module Day3 where
+
+import System.Environment (getArgs)
+
+data Square = Empty | Tree
+    deriving (Eq, Ord, Show)
+
+type Map = [[Square]]
+
+-- Converts lines to a map
+toMap :: [String] -> Map
+toMap = map toRow
+        where toRow = map toSquare
+              toSquare '.' = Empty
+              toSquare '#' = Tree
+              toSquare _ = error "Invalid map character"
+
+-- Get the size of a map
+-- Note this returns (height, width)
+getSize :: Map -> (Int, Int)
+getSize m = (length m, length (head m))
+
+-- Get the square at the given (y, x) coord
+-- This wraps the x coord, but not the y
+get :: Map -> Int -> Int -> Square
+get m y x = m!!y!!(x `mod` w)
+              where (_, w) = getSize m
+
+-- Get the squares encountered along a slop, starting at (y, x)
+-- and descending along (f, r)
+getSquaresAlongSlope :: Map -> Int -> Int -> Int -> Int -> [Square]
+getSquaresAlongSlope m y x f r | y >= h = []
+                               | otherwise = get m y x : getSquaresAlongSlope m (y + f) (x + r) f r
+                                    where (h, _) = getSize m
+
+-- Count the number of trees along a given slope, starting at (0, 0)
+checkSlope :: Map -> Int -> Int -> Int
+checkSlope m f r = length $ filter (== Tree) $ getSquaresAlongSlope m 0 0 f r
+
+-- Usage: ./3b inputs/day3
+main :: IO ()
+main = do
+        args <- getArgs;
+        content <- readFile $ head args;
+        let l = lines content;
+        let m = toMap l;
+        print $ product $ map (uncurry $ checkSlope m) [(1, 1), (1, 3), (1, 5), (1, 7), (2, 1)]
+        return ()
\ No newline at end of file
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