1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24type Grid = [[Char]]
isTree :: Grid -> Int -> Int -> Integer
isTree grid row col =
let rowList = grid !! row
in case rowList !! (col `mod` length rowList) of -- mod to handle the "repeating"
'.' -> 0
'#' -> 1
stepCount :: Grid -> Int -> Int -> Int -> Int -> Integer
stepCount grid down right row col =
let row' = row + down
col' = col + right
in if row' >= length grid -- stop once we reach the bottom
then 0
else isTree grid row' col' + stepCount grid down right row' col'
main :: IO ()
main = do
input <- readFile "input.txt"
let grid = lines input
execSlope right down = stepCount grid down right 0 0
print $ execSlope 3 1
print . product . map (uncurry execSlope) $ [(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)]