AoC/2019/day3/day3.hs

import Data.List.Split
import Data.List
import qualified Data.Set as Set
import Data.Maybe

main = do
    content <- readFile "input"
    let input = map (splitOn ",") (lines content)
    let parsedinput = map (map parseone) input
    let trace1 = tracewire (head parsedinput) (0,0) [(0,0)]
    let trace2 = tracewire (last parsedinput) (0,0) [(0,0)]
    print (day3a trace1 trace2)
    print (day3b trace1 trace2)


parseone :: String -> (Char, Int)
parseone xs = (head xs, read $ tail xs)

tracewire :: [(Char,Int)] -> (Int,Int) -> [(Int,Int)] -> [(Int,Int)]
tracewire [] _ x = x
tracewire ((x,n):xs) (accx,accy) trc
    | x=='U'=tracewire xs (accx,accy+n) (trc++[(accx,accy+i) | i<-[1..n]])
    | x=='R'=tracewire xs (accx+n,accy) (trc++[(accx+i,accy) | i<-[1..n]])
    | x=='D'=tracewire xs (accx,accy-n) (trc++[(accx,accy-i) | i<-[1..n]])
    | x=='L'=tracewire xs (accx-n,accy) (trc++[(accx-i,accy) | i<-[1..n]])

day3a :: [(Int,Int)] -> [(Int,Int)] -> Int
day3a xs ys = Set.findMin $ Set.map manhattan (intersections xs ys)
    where manhattan (x,y) = abs x + abs y

intersections :: [(Int,Int)] -> [(Int,Int)] -> Set.Set (Int, Int)
intersections xs ys = Set.delete (0,0) crossset
    where crossset = (Set.fromList xs) `Set.intersection` (Set.fromList ys)

day3b xs ys = minimum [let f = fromJust . findIndex (==x) in f xs + f ys
                       | x<-Set.toList $ intersections xs ys]