In progress

day3/main.hs

@@ -5,6 +5,8 @@
 
 {-# LANGUAGE OverloadedStrings #-}
 
+import Data.List (intersperse)
+
 testData :: [String]
 testData = [ "..##......."
            , "#...#...#.."
@@ -19,7 +21,61 @@ testData = [ "..##......."
            , ".#..#...#.#"
            ]
 
+data Position = Position { x_::Int, y_::Int }
+
+instance Show (Position)
+  where
+    show p = "("<>show (x_ p)<>","<>show (y_ p)<>")"
+
+-- Returns a half-line starting on (0,0) and following the (x*a,x*b) eq:
+line :: Int -> Int -> [Position]
+line a b = Position 0 0 : [ Position (x*a) (x*b) | x <- [1..] ]
+
+-- Starting at the top-left corner of your map and following a slope of right 3
+-- and down 1, how many trees would you encounter?
+
+-- Requirements for this first task:
+-- - datastructure supporting random-access (or similar) interface (lists would work)
+-- - function generating a list of (x,y) coordinate to check
+-- - must have 2D datastructure, since it's infinite on 1D (x axis)
+-- - in this version at least, there's no need to modify the datastructure, so
+--   it can be read-only, or even just a function taking a position and returning
+--   SquareSortEmpty or SquareSortTree
+
+data SquareSort = SquareSortTree | SquareSortEmpty
+
+instance Show SquareSort
+  where
+    show SquareSortTree   = "#"
+    show SquareSortEmpty  = "."
+
+char2ss :: Char -> Maybe SquareSort
+char2ss '#' = Just SquareSortTree
+char2ss '.' = Just SquareSortEmpty
+char2ss _ = Nothing
+
+str2sss :: String -> Maybe [SquareSort]
+str2sss = sequence . (map char2ss)
+
+newtype Grid = Grid [[SquareSort]]
+
+instance Show (Grid)
+  where
+    show (Grid x) = intersperse '\n' $ map show x
+
+parseInput :: [String] -> Maybe Grid
+parseInput x = Grid <$> sequence ( (map str2sss) x )
+
+getSquareSortAtPosition :: Grid -> Position -> SquareSort
+getSquareSortAtPosition (Grid grid) (Position x y) =
+  grid !! y !! (x `mod` n)
+  where
+    n = length (grid !! 0)
+
 main :: IO ()
 main = do
   putStrLn "Day 3 - Part 1"
-  print testData
+  print $ take 5 $ line 3 1
+  let (Just parsedTestData) = parseInput testData
+  print parsedTestData
+  print $ getSquareSortAtPosition parsedTestData (Position 3 0)