Submission #19440021

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Source Code Expand

{-# LANGUAGE DatatypeContexts #-}
import           Control.Exception           (assert)
import           Control.Monad
import           Control.Monad.Primitive
import qualified Control.Monad.ST            as ST
import qualified Data.Array.IO               as IO
import qualified Data.Array.ST               as ST
import qualified Data.Array.Unboxed          as A
import           Data.Bits
import qualified Data.ByteString.Char8       as BS
import           Data.Char
import           Data.Foldable
import           Data.List
import qualified Data.Map.Strict             as Map
import           Data.Maybe
import qualified Data.Sequence               as Seq
import qualified Data.Set                    as Set
import qualified Data.Vector                 as VB
import qualified Data.Vector.Mutable         as VBM
import qualified Data.Vector.Unboxed         as V
import           Data.Vector.Unboxed.Base
import qualified Data.Vector.Unboxed.Mutable as VM
import           Debug.Trace

readInt = fst . fromJust . BS.readInt
readIntList = map readInt . BS.words
getInt = readInt <$> BS.getLine
getIntList = readIntList <$> BS.getLine
getIntVec n = V.unfoldrN n (BS.readInt . BS.dropWhile isSpace) <$> BS.getLine

readInteger = fst . fromJust . BS.readInteger
readIntegerList = map readInteger . BS.words
getInteger = readInteger <$> BS.getLine
getIntegerList = readIntegerList <$> BS.getLine

inf :: Int
inf = 10^18

main = do
  [n, u', v'] <- getIntList
  let (u, v) = (u'-1, v'-1)

  ess <- VBM.new n
  VBM.set ess ([]::[Int])

  replicateM_ (n-1) $ do
    [a, b] <- getIntList
    let ia = a - 1
        ib = b - 1
    ta <- VBM.read ess ia
    VBM.write ess ia (ib:ta)
    tb <- VBM.read ess ib
    VBM.write ess ib (ia:tb)

  da <- VM.new n
  VM.set da inf
  dt <- VM.new n
  VM.set dt inf

  let dfs d d' par i dist = do
        t <- VM.read d i
        if (t > dist)
          then do
          VM.write d i dist
          es <- VBM.read ess i
          let es' = filter (/=par) es
          if null es' -- if Leaf
            then do t' <- VM.read d' i
                    let r | t' == 0 = dist - 1
                          | dist >= t' = 0
                          | otherwise = t' - 1
                    return r
            else do bs <- forM es' $ \j -> dfs d d' i j (dist+1)
                    return $ maximum bs
          else return 0

  dfs da dt (-1) v 0
  ans <- dfs dt da (-1) u 0
  print ans

Submission Info

Compile Error

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

Main.hs:1:14: warning:
    -XDatatypeContexts is deprecated: It was widely considered a misfeature, and has been removed from the Haskell language.
  |
1 | {-# LANGUAGE DatatypeContexts #-}
  |              ^^^^^^^^^^^^^^^^

Judge Result