AoC/2019/day6/day6.hs

import Data.List.Split
import Data.List
import Data.Maybe

main = do
    content <- (map (splitOn ")") . lines) <$> readFile "input"
    print $ day6a content
    print $ day6b content

day6a l = sum $ map (day6a' (transpose l) l) l
day6a' l l2 (s:t)
    | s `elem` (l!!1) = 1 + day6a' l l2 next_pair
    | otherwise       = 1
    where next_pair = l2 !! (fromJust $ elemIndex s (l!!1))

day6b :: [[String]] -> Int
day6b l = day6b' l "YOU" "SAN" [] - 2
day6b' l s t visited
    | [s,t]`elem`l||[t,s]`elem`l=1
    | otherwise = 1 + minimum next_nodes
    where neighbours a = filter (/=a) $ concat
                        [if x==a then xs else [] | xs<-l, x<-xs]
          next_nodes = [if x `elem` visited then maxBound -1
                        else day6b' l x t (x:visited)| x<-neighbours s]