Problem:
Problem B: Red and Black

There is a rectangular room, covered with square tiles. Each tile is
colored either red or black. A man is standing on a black tile.
From a tile, he can move to one of four adjacent tiles. But he can't
move on red tiles, he can move only on black tiles.

Write a program to count the number of black tiles which he can reach
by repeating the moves described above.

Input

The input consists of multiple data sets.
A data set starts with a line containing two positive integers W and H;
W and H are the numbers of tiles in the x-
and y- directions, respectively. W and H are
not more than 20.

There are H more lines in the data set, each of which
includes W characters. Each character represents the color of a
tile as follows.

'.' - a black tile

'#' - a red tile

'@' - a man on a black tile(appears exactly once in a data set)

The end of the input is indicated by a line consisting of two zeros.

Output

For each data set, your program
should output a line which contains the number of
tiles he can reach from the initial tile (including itself).

Sample Input

6 9
....#.
.....#
......
......
......
......
......
#@...#
.#..#.
11 9
.#.........
.#.#######.
.#.#.....#.
.#.#.###.#.
.#.#..@#.#.
.#.#####.#.
.#.......#.
.#########.
...........
11 6
..#..#..#..
..#..#..#..
..#..#..###
..#..#..#@.
..#..#..#..
..#..#..#..
7 7
..#.#..
..#.#..
###.###
...@...
###.###
..#.#..
..#.#..
0 0

Output for the Sample Input

45
59
6
13

Solution in Haskell (judge verdict: Accepted)

{-
URL: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1130&lang=jp
?????????: Red and Black
?????°
19:08:06 ??¶?´???????????????§Haskell??§??????????????????
19:17:53 ??¨??????????????????????????¨?????´??°??????bar???????£?????????????
19:32:19 ????????????
19:34:02 ??????fmap???????????????
-}
import Control.Monad
import Control.Applicative
import Data.List

main :: IO ()
main = do
 [w,h] <- (map read . words) `fmap` getLine
 when ((w,h) /= (0,0)) $ do
  arr <- replicateM h getLine
  print $ foo arr
  main

type Stat = (Integer, [[Char]])

foo :: [[Char]] -> Integer
foo arr = fst $ repetitive bar (1,arr)

repetitive :: Eq t => (t -> t) -> t -> t --??????????????????????????§?????¨????????????????±???????
repetitive f s = if f s == s then s else repetitive f (f s)

bar :: Stat -> Stat -- "@"????????????"."???"@"?????????
bar = f . f
 where f = fmap transpose . bar1 ".@" . bar1 "@."

bar1 :: String -> Stat -> Stat -- replace all `bef` with "@@", while counting the num
bar1 bef (num, dat) = (num + sum(map fst d'), map snd d')
 where 
  d' = map f dat
  f :: String -> (Integer,String)
  f str
   | null str = (0,"")
   | bef `isPrefixOf` str = count $ ("@@" ++) `fmap` f(drop 2 str)
   | otherwise = (head str :) `fmap` f (tail str)

count :: (Integer,a) -> (Integer,a)
count(a,b)=(a+1,b)