diff options
Diffstat (limited to '2020/03b.hs')
| -rw-r--r-- | 2020/03b.hs | 48 |
1 files changed, 48 insertions, 0 deletions
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 |