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オフラインリアルタイムどう書く第5回の参考問題の回答例（Haskell)

Posted at 2012-10-21

問題はこちら。 http://qiita.com/items/0ddde0164a745cd09c34

Ruby版の回答 ( http://qiita.com/items/ed5fa743164638de72b1 ) をHaskellに翻訳してみました。

左右の番兵をひとつですませる発想はなかったので、ちょっと新鮮でした。
ハッシュのかわりにパタンマッチングを使っています（なのでちょっと行数増えました）。


import Data.Char
import Test.HUnit

board = "----ABC-DEF-GHI----"

move 0   4  =  4
move 0 (-4) = -4
move 0   1  =  1
move 0 (-1) = -1
move 1   4  =  1
move 1 (-4) = -1
move 1   1  =  4
move 1 (-1) = -4
move 2   4  = -1
move 2 (-4) =  1
move 2   1  = -4
move 2 (-1) =  4

solve xs = solve' 5 4
    where
        solve' pos mv
            | pat !! pos < 0 = []
            | otherwise      = let mv'  = move (pat !! pos) mv
                                   pos' = pos + mv'
                               in  (board !! pos):(solve' pos' mv')
        pat = replicate 4 (-1) ++ (pat' $ map ((subtract 48).ord) xs)
        pat' []        = replicate 4 (-1)
        pat' (a:b:c:t) = a:b:c:(-1):(pat' t)

main = do
    runTestTT $ test $ map (\(e, a) -> e ~=? solve a) testPattern
    return ()

testPattern = [ ("BEDGHIFEH",   "101221102")
              , ("BEH",         "000000000")
              , ("BCF",         "111111111")
              , ("BAD",         "222222222")
              , ("BEFIHEDGH",   "000211112")
              , ("BADGHIFEBCF", "221011102")
              , ("BEHIFCBADEF", "201100112")
              , ("BEFIH",       "000111222")
              , ("BC",          "012012012")
              , ("BEDABCFI",    "201120111")
              , ("BADEHGD",     "220111122")
              , ("BADG",        "221011022")
              , ("BCFIHEBA",    "111000112")
              , ("BEFI",        "001211001")
              , ("BCFEHIF",     "111222012")
              , ("BADEHI",      "220111211")
              , ("BCFEBAD",     "211212212")
              , ("BEFC",        "002112210")
              , ("BEF",         "001010221")
              , ("BEFIHG",      "100211002")
              , ("BEFCBAD",     "201212121")
              ]

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