Submission #35132576

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Source Code Expand

import Control.Monad
import Data.Maybe
import qualified Data.ByteString.Char8 as BS
import Data.List
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM
import qualified Data.Vector as V
import qualified Data.Vector.Mutable as VM
import qualified Data.Sequence as Sq

readInt = fst . fromJust . BS.readInt
readIntList = map readInt . BS.words
getInt = readInt <$> BS.getLine
getIntList = readIntList <$> BS.getLine

main = do
    [n, x, y] <- getIntList
    uv <- replicateM (n-1) $ do
        [u, v] <- getIntList
        return (u-1, v-1)

    let edges = V.create $ do
            vec <- VM.replicate n []
            forM_ uv $ \(a,b) -> do
                VM.modify vec (a:) b
                VM.modify vec (b:) a
            return vec

    let result = VU.create $ do
            vec <- VUM.replicate n ((-1) :: Int)
            let go Sq.Empty = return ()
                go ((p, this) Sq.:<| qs) = do
                    VUM.write vec this p
                    go . foldl (Sq.|>) qs . map (\t -> (this, t)) $ filter (/= p) (edges V.! this)
            go (Sq.singleton (-2, x-1))
            return vec

    let path = reverse $ loop (y-1)
            where loop v | v < 0 = []
                         | otherwise = (v+1) : loop (result VU.! v)
    putStrLn . unwords $ map show path

Submission Info

Compile Error

Loaded package environment from /home/contestant/.ghc/x86_64-linux-8.8.3/environments/default

Judge Result