Submission #51785046

---

Source Code Expand

import Control.Monad
import qualified Data.ByteString.Char8 as BS
import Data.Char
import Data.List

import Data.Array
import qualified Data.Set as S

main :: IO ()
main = do
  nm <- bsGetLnInts
  uvs <- replicateM (nm !! 1) bsGetLnInts
  st <- bsGetLnInts
  let ans = abc132e (nm ++ st) uvs
  print ans

bsGetLnInts :: IO [Int]
bsGetLnInts = unfoldr (BS.readInt . BS.dropWhile isSpace) <$> BS.getLine


abc132e :: [Int] -> [[Int]] -> Int
abc132e [n,m,s,t] uvs = bfs 0 (S.singleton start) [start] []
  where
    g = accumArray (flip (:)) [] (1,n) [(u, v) | u:v:_ <- uvs]
    start = (s,0)
    goal  = (t,0)
    bfs :: Int -> S.Set (Int,Int) -> [(Int,Int)] -> [(Int,Int)] -> Int
    bfs _nt _ [] [] = -1                                       -- 経路なし
    bfs cnt visited [] nexts = bfs (succ cnt) visited nexts [] -- BFSを一段進める
    bfs cnt visited (uk@(u,k):uks) nexts
      | uk == goal = div cnt 3                                 -- ゴールしたら距離/3が答え
      | otherwise = bfs cnt visited1 uks nexts1
      where
        j = mod (succ k) 3
        vjs = [vj | v <- g ! u, let vj = (v,j), notElem vj visited]
        visited1 = S.union visited $ S.fromList vjs
        nexts1 = vjs ++ nexts

{-
格調高くやる。
-}

Submission Info

Compile Error

app/Main.hs:22:1: warning: [-Wincomplete-patterns]
    Pattern match(es) are non-exhaustive
    In an equation for ‘abc132e’:
        Patterns of type ‘[Int]’, ‘[[Int]]’ not matched:
            [] _
            [_] _
            [_, _] _
            [_, _, _] _
            ...
   |
22 | abc132e [n,m,s,t] uvs = bfs 0 (S.singleton start) [start] []
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...

app/Main.hs:22:12: warning: [-Wunused-matches]
    Defined but not used: ‘m’
   |
22 | abc132e [n,m,s,t] uvs = bfs 0 (S.singleton start) [start] []
   |            ^

Judge Result