advent_day_03.hs

module Main where

import Data.Maybe
import Data.List

main = do
    content <- getContents
    -- get rid of \n
    let c = init content
    putStr "Single Santa traveled: "
    print . length . nub . strToAddresses $ c
    putStr "Double Santa traveled: "
    let (santaDirections, robosantaDirections)  = splitList c
    print . length . nub $ strToAddresses santaDirections ++ strToAddresses robosantaDirections

data Address = Address Int Int
instance Eq Address where
	(Address x1 y1) == (Address x2 y2) = x1 == x2 && y1 == y2

data Direction = North | South | East | West

charToDirection :: Char -> Maybe Direction
charToDirection '^' = Just North
charToDirection 'v' = Just South
charToDirection '>' = Just East
charToDirection '<' = Just West
charToDirection _ = Nothing

move :: Address -> Direction -> Address
move (Address x y) North = Address x (y + 1)
move (Address x y) South = Address x (y - 1)
move (Address x y) East = Address (x + 1) y
move (Address x y) West = Address (x - 1) y

strToAddresses :: String -> [Address]
strToAddresses xs = foldr (((\ d (x : xs) -> move x d : x : xs) . fromJust) .  charToDirection) [Address 0 0] xs 

splitList :: [a] -> ([a], [a])
splitList xs = splitListHelper xs ([], [])

-- inefficient way to split a list on odds and evens!
-- length is a slow operation
splitListHelper :: [a] -> ([a], [a]) -> ([a], [a])
splitListHelper [] xs = xs
splitListHelper (x:xs) (ys, zs)
	| length ys == length zs = splitListHelper xs (x:ys, zs)
	| otherwise = splitListHelper xs (ys, x:zs)