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 PHP (judge verdict: WA: Presentation Error)

<?php
$dy = array( -1, 0, 1, 0);
$dx = array( 0, 1, 0, -1);
while(fscanf( STDIN, "%d %d\n", $w, $h) && $w){
  for($i = 0 ; $i < $h ; $i++ ){
    fscanf( STDIN, "%s\n", $mas[$i]);
    for($j = 0 ; $j < $w ; $j++ ){
      if($mas[$i][$j] == '@'){
        $sy = $i;
        $sx = $j;
      }
      $used[$i][$j] = false;
    }
  }
  $que = new SplQueue();
  $que -> push(array($sy,$sx));
  $cnt = 0;
  while(!$que -> isEmpty()){
    $p = $que -> dequeue();
    if($used[$p[0]][$p[1]]) continue;
    $used[$p[0]][$p[1]] = true;
    $cnt++;
    for($i = 0 ; $i < 4 ; $i++ ){
      $ny = $p[0] + $dy[$i];
      $nx = $p[1] + $dx[$i];
      if($ny >= 0 && $ny < $h && $nx >= 0 && $nx < $w && $mas[$ny][$nx] == '.'){
        $que -> push(array($ny,$nx));
      }
    }
  }
  echo "$cnt\n";
}
?>