day 5

Signed-off-by: Jack Bond-Preston <jackbondpreston@outlook.com>

5/5.hs

@@ -0,0 +1,74 @@
+import System.IO
+    ( hClose, openFile, hGetContents, IOMode(ReadMode) )
+import Text.Parsec
+import Text.Parsec.String
+import Control.Monad
+import Data.List
+import Data.Maybe
+import Data.Sequence (replicate, Seq, mapWithIndex)
+
+import Data.Map (Map, (!))
+import qualified Data.Map as Map
+
+type Coord     = (Int, Int)
+type LineEnds  = (Coord, Coord)
+
+type Grid       = Map Coord Integer
+
+int :: Parser Int
+int = read <$> many1 digit
+
+eol :: Parser ()
+eol = void $ char '\n'
+
+coord :: Parser Coord
+coord = do
+    x <- int
+    char ','
+    y <- int
+
+    return (x, y)
+
+arrow :: Parser ()
+arrow = void $ string " -> "
+
+line :: Parser LineEnds
+line = do
+    from <- coord
+    arrow
+    to <- coord
+
+    return (from, to)
+
+inputParser :: Parser [LineEnds]
+inputParser = line `endBy1` eol
+
+lineToCellList :: LineEnds -> [Coord]
+lineToCellList ((x0, y0), (x1, y1))
+    | x0 == x1  = [ (x0, y) | y <- [min y0 y1 .. max y0 y1] ]
+    | y0 == y1  = [ (x, y0) | x <- [min x0 x1 .. max x0 x1] ]
+    | otherwise = [ (x, y)  | x <- [min x0 x1 .. max x0 x1],
+                              y <- [min y0 y1 .. max y0 y1],
+                              abs (x - x0) == abs (y - y0) ]
+
+type CoordMap = Map Coord Int
+
+scoreFold :: Coord -> (CoordMap, Int) -> (CoordMap, Int)
+scoreFold coord (map, acc) 
+    | Map.member coord map = if
+        (map ! coord) == 1 then (Map.adjust (+1) coord map, acc + 1)
+        else                    (Map.adjust (+1) coord map, acc)
+    | otherwise            = (Map.insert coord 1 map, acc)
+
+score :: [LineEnds] -> Int
+score les = snd (foldr scoreFold (Map.empty, 0) coords)
+    where
+        coords = concatMap lineToCellList les
+
+main = do
+    handle <- openFile "input.txt" ReadMode
+    contents <- hGetContents handle
+    case parse inputParser "" contents of
+        Left x -> print x
+        Right x -> print (score x)
+    hClose handle