Solve day 3, part 2

Solve day 3, part 1
4 changed files with 398 additions and 1 deletions
--- a/AdventOfCode2020.cabal
+++ b/AdventOfCode2020.cabal
@ -17,13 +17,14 @@ maintainer:          gael@depreeuw.dev
 extra-source-files:  CHANGELOG.md, README.md
 library
-  exposed-modules:     Day1, Day2
+  exposed-modules:     Day1, Day2, Day3
  -- other-modules:
  -- other-extensions:
  build-depends:       base ^>=4.13.0.0
                     , containers ^>=0.6.4.1
                     , text ^>=1.2.4.0
                     , attoparsec ^>=0.13.2.4
                     , vector ^>=0.12.1.2
  hs-source-dirs:      src
  default-language:    Haskell2010
--- a/Main.hs
+++ b/Main.hs
@ -2,8 +2,10 @@ module Main where
 import Day1 (day1)
 import Day2 (day2)
 import Day3 (day3)
 main :: IO ()
 main = do
  day1
  day2
  day3
--- a/input/day3
+++ b/input/day3
@ -0,0 +1,323 @@
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--- a/src/Day3.hs
+++ b/src/Day3.hs
@ -0,0 +1,71 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE OverloadedStrings #-}
 module Day3 (day3) where
 import Control.Applicative ((<|>))
 import qualified Data.Attoparsec.Text as P
 import qualified Data.Text as T
 import qualified Data.Vector as V
 import Numeric.Natural (Natural)
 data Loc = Tree | Open deriving (Show, Eq)
 type Hor = V.Vector Loc
 type Grid = V.Vector Hor
 parserLoc :: P.Parser Loc
 parserLoc = do
  loc <- P.char '.' <|> P.char '#'
  case loc of
    '.' -> return Open
    '#' -> return Tree
 parserLine :: P.Parser Hor
 parserLine = do
  locs <- P.many1 parserLoc
  return $ V.fromList locs
 parserGrid :: P.Parser Grid
 parserGrid = do
  grid <- parserLine `P.sepBy` P.endOfLine
  return $ V.fromList grid
 slideDown ::
  (Natural, Natural) ->
  (Natural, Natural) ->
  Grid ->
  Maybe [Loc] ->
  Maybe [Loc]
 slideDown _ _ _ Nothing = Nothing
 slideDown (x, y) (x'inc, y'inc) g (Just r)
  | y >= (fromIntegral . length) g = Just r
  | otherwise = do
    hor <- g V.!? fromIntegral y
    let x' = x `mod` (fromIntegral . length) hor
    loc <- hor V.!? fromIntegral x'
    slideDown (x' + x'inc, y + y'inc) (x'inc, y'inc) g (Just (r ++ [loc]))
 countTrees :: [Loc] -> Int
 countTrees = length . filter (== Tree)
 parseGrid :: String -> Grid
 parseGrid s =
  case P.parseOnly parserGrid (T.pack s) of
    Left s -> error (show s)
    Right r -> r
 day3 :: IO ()
 day3 = do
  r <- readFile "./input/day3"
  let grid = parseGrid r
  putStr "[Day 3-1] # trees: "
  case slideDown (0, 0) (3, 1) grid (Just []) of
    Nothing -> putStrLn "ERROR"
    Just locs -> print . countTrees $ locs
  putStr "[Day 3-2] # trees: "
  let mTrees = mapM (\x -> slideDown (0, 0) x grid (Just [])) [(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)]
  case mTrees of
    Nothing -> putStrLn "ERROR"
    Just trees -> print . product $ map countTrees trees
Author	SHA1	Message	Date
Gaël Depreeuw	40c5f7b10f	Solve day 3, part 2	4 years ago
Gaël Depreeuw	a9b566e9ad	Solve day 3, part 1	4 years ago