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 Scala (judge verdict: Accepted)

object Main {
  def bfs(ar: Array[String], x: Int, y: Int, w: Int, h: Int): Array[String] = {
    if (x < 0 || x >= w || y < 0 || y >= h)
      return ar
    if (ar(y)(x) != '.')
      return ar
    // ????????\?????????????????????????????????????????£???
    var br = ar
    br(y) = br(y).patch(x, "C", 1)
    br = bfs(br, x - 1, y, w, h)
    br = bfs(br, x + 1, y, w, h)
    br = bfs(br, x, y + 1, w, h)
    br = bfs(br, x, y - 1, w, h)
    return br
  }


  def solve(ar: Array[String], room: Array[Int]): Int = {
    var x = -1
    var y = -1
    for(i <- 0 until ar.length) {
      val tmp = ar(i).indexOf('@')
      if (tmp != -1) {
        x = tmp
        y = i
      }
    }
    var br = ar
    br(y) = br(y).patch(x, ".", 1)
    br = bfs(br, x, y, room(0), room(1))
    var cnt = 0
    for(res <- br)
      cnt += res.count{_ == 'C'}
    cnt
  }

  def main(args: Array[String]) = {
    var room = io.StdIn.readLine().split(' ').map(_.toInt)
    while (room(0) != 0) {
      val ar = new Array[String](room(1))
      for (i <- 0 until room(1))
        ar(i) = io.StdIn.readLine()
      println(solve(ar, room))
      room = io.StdIn.readLine().split(' ').map(_.toInt)
    }
  }
}