121 lines
3.7 KiB
Haskell
Executable file
121 lines
3.7 KiB
Haskell
Executable file
#! /usr/bin/env -S"ANSWER=42" nix-shell
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#! nix-shell -p ghcid
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#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [])"
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#! nix-shell -i "ghcid -c 'ghci -Wall' -T main"
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{-# LANGUAGE OverloadedStrings #-}
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import Data.List (intersperse)
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testData :: [String]
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testData = [ "..##......."
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, "#...#...#.."
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, ".#....#..#."
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, "..#.#...#.#"
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, ".#...##..#."
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, "..#.##....."
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, ".#.#.#....#"
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, ".#........#"
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, "#.##...#..."
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, "#...##....#"
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, ".#..#...#.#"
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]
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data Position = Position { x_::Int, y_::Int }
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instance Show (Position)
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where
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show p = "("<>show (x_ p)<>","<>show (y_ p)<>")"
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-- Returns a half-line starting on (0,0) and following the (x*a,x*b) eq:
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line :: Int -> Int -> [Position]
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line a b = Position 0 0 : [ Position (x*a) (x*b) | x <- [1..] ]
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-- Starting at the top-left corner of your map and following a slope of right 3
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-- and down 1, how many trees would you encounter?
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-- Requirements for this first task:
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-- - datastructure supporting random-access (or similar) interface (lists would work)
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-- - function generating a list of (x,y) coordinate to check
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-- - must have 2D datastructure, since it's infinite on 1D (x axis)
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-- - in this version at least, there's no need to modify the datastructure, so
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-- it can be read-only, or even just a function taking a position and returning
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-- SquareSortEmpty or SquareSortTree
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data SquareSort = SquareSortTree | SquareSortEmpty
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deriving Eq
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instance Show SquareSort
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where
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show SquareSortTree = "#"
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show SquareSortEmpty = "_"
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char2ss :: Char -> Maybe SquareSort
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char2ss '#' = Just SquareSortTree
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char2ss '.' = Just SquareSortEmpty
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char2ss _ = Nothing
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str2sss :: String -> Maybe [SquareSort]
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str2sss = sequence . (map char2ss)
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newtype Grid = Grid [[SquareSort]]
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instance Show (Grid)
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where
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show (Grid x) = concat $ intersperse "\n" $ map show x
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parseInput :: [String] -> Maybe Grid
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parseInput x = Grid <$> sequence ( (map str2sss) x )
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getSquareSortAtPosition :: Grid -> Position -> SquareSort
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getSquareSortAtPosition (Grid grid) (Position x y) =
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grid !! y !! (x `mod` n)
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where
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n = length (grid !! 0)
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solveDay3Part1 :: Grid -> (Int,Int) -> Int
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solveDay3Part1 grid@(Grid lx) (x',y')=
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length $ filter (== SquareSortTree) $ map (getSquareSortAtPosition grid) px
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where
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px = take n' $ line x' y'
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n' = if y' > 1 then n + 1 else n
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n = (length lx) `div` y'
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-- Determine the number of trees you would encounter if, for each of the
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-- following slopes, you start at the top-left corner and traverse the map all
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-- the way to the bottom:
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--
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-- - Right 1, down 1.
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-- - Right 3, down 1. (This is the slope you already checked.)
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-- - Right 5, down 1.
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-- - Right 7, down 1.
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-- - Right 1, down 2.
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--
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-- What do you get if you multiply together the number of trees encountered on
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-- each of the listed slopes?
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solveDay3Part2 :: Grid -> Int
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solveDay3Part2 grid =
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foldl (*) 1 [ solveDay3Part1 grid (1,1)
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, solveDay3Part1 grid (3,1)
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, solveDay3Part1 grid (5,1)
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, solveDay3Part1 grid (7,1)
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, solveDay3Part1 grid (1,2)
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]
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main :: IO ()
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main = do
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putStrLn "Day 3 - Part 1"
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inputData <- readFile "day3/input"
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print $ take 5 $ line 3 1
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print $ take 6 $ line 1 2
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let (Just parsedTestData) = parseInput testData
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print parsedTestData
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print $ getSquareSortAtPosition parsedTestData (Position 5 10)
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let (Just parsedInputData) = parseInput (lines inputData)
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putStrLn "Part 1:"
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print $ solveDay3Part1 parsedTestData (3,1)
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print $ solveDay3Part1 parsedInputData (3,1)
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putStrLn "Part 2:"
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print $ solveDay3Part2 parsedTestData
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print $ solveDay3Part2 parsedInputData
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