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 JAVA (judge verdict: Wrong Answer)

import java.util.*;
public class Main {
	int[][] land,looked;
	int sx,sy,w,h,count;
	int[] dx={-1,1,0,0},dy={0,0,-1,1};
	
	Scanner stdin =new Scanner(System.in);
	Queue qx=new LinkedList();Queue qy=new LinkedList();
	
	
	void Solve(){
		
		while(true){
			w=stdin.nextInt();
			h=stdin.nextInt();
			if(w==0&&h==0) break;
			land=new int[h][w];
			looked=new int[h][w];
			count=1;
			
			for(int i=0;i<h;i++){
				String s=stdin.next();
				for(int j=0;j<w;j++){
					if(s.charAt(j)=='.') land[i][j]=1;
					else if(s.charAt(j)=='@'){
						land[i][j]=0;
						sx=i;
						sy=j;
					}else land[i][j]=0;
				}
			}
			
		}
		
		looked=land.clone();
		//System.out.println(land[5][8]);
		bfs(sx,sy);
		System.out.println(count);
		
		
		
		
		
	}
	
	void bfs(int sx,int sy){
		//System.out.println(sx+" "+sy);
		looked[sx][sy]=0;
		for(int i=0;i<4;i++){
			int xx=sx+dx[i];
			int yy=sy+dy[i];
			if(0<=xx&&xx<h&&0<=yy&&yy<w){
				if(land[xx][yy]==1){
					if(looked[xx][yy]==1)count++;
					bfs(xx,yy);
				}
			}
		}
	}
	
	public static void main(String args[]){
		Main m=new Main();
		m.Solve();
	}
}