オフラインリアルタイムどう書く第5回の参考問題をArcで解く

気がついたら明日だったので、Arcで解いてみた。
問題はこちら
http://qiita.com/items/0ddde0164a745cd09c34

```arc:realtime_doukaku5.arc
(= opposite '(2 3 0 1))
(= pattern '((2 3 0 1) (1 0 3 2) (3 2 1 0)))
(= adjacent (list [if (< -1 (- _ 3)) (- _ 3)]   ; up                                                                                                                              
                  [if (< (mod _ 3) 2) (++ _)]   ; right                                                                                                                           
                  [if (< (+ _ 3) 9) (+ _ 3)]    ; down                                                                                                                             
                  [if (< 0 (mod _ 3)) (-- _)])) ; left                                                                                                                            

(def run (lis idx side)
  (let next ((pattern (lis idx)) side)
    (cons idx
          (aif ((adjacent next) idx)
               (run lis it (opposite next))))))

(def to-alphabet (l) (upcase (string (map [coerce (+ _ 97) 'char] l))))
(def to-numlis (s) (read (+ "(" (string (intersperse #\  (coerce s 'cons))) ")")))
(def solve (s) (to-alphabet (run (to-numlis s) 1 0)))
```

以上が算出のコード
普通に書いたつもりだがなんかショートコードっぽくなるな…

```arc:realtime_doukaku_5_result.arc
(solve "101221102") ;-> "BEDGHIFEH"                                                                                                                                               
(solve "000000000") ;-> "BEH"                                                                                                                                                     
(solve "111111111") ;-> "BCF"                                                                                                                                                     
(solve "222222222") ;-> "BAD"                                                                                                                                                     
(solve "000211112") ;-> "BEFIHEDGH"                                                                                                                                               
(solve "221011102") ;-> "BADGHIFEBCF"                                                                                                                                             
(solve "201100112") ;-> "BEHIFCBADEF"                                                                                                                                             
(solve "000111222") ;-> "BEFIH"                                                                                                                                                   
(solve "012012012") ;-> "BC"                                                                                                                                                      
(solve "201120111") ;-> "BEDABCFI"                                                                                                                                                
(solve "220111122") ;-> "BADEHGD"                                                                                                                                                 
(solve "221011022") ;-> "BADG"                                                                                                                                                    
(solve "111000112") ;-> "BCFIHEBA"                                                                                                                                                
(solve "001211001") ;-> "BEFI"                                                                                                                                                    
(solve "111222012") ;-> "BCFEHIF"                                                                                                                                                 
(solve "220111211") ;-> "BADEHI"                                                                                                                                                  
(solve "211212212") ;-> "BCFEBAD"                                                                                                                                                 
(solve "002112210") ;-> "BEFC"                                                                                                                                                    
(solve "001010221") ;-> "BEF"                                                                                                                                                     
(solve "100211002") ;-> "BEFIHG"                                                                                                                                                  
(solve "201212121") ;-> "BEFCBAD"  
```

以上が検証コード
うまく動いている。