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: Accepted)

import java.util.*;class Main{public static void main(String[]z){Scanner s=new Scanner(System.in);char[][]a;for(int w,h,x,y,i,j;(w=s.nextInt()+2)>2;System.out.println(f(a,x,y))){a=new char[h=s.nextInt()+2][w];for(i=x=y=1;i<h-1;++i){j=0;for(char c:s.next().toCharArray()){a[i][++j]=c=='#'?0:c;if(a[i][j]>63){x=i;y=j;}}}}}static int f(char[][]a,int x,int y){if(a[x][y]<1)return 0;a[x][y]=0;return f(a,x-1,y)+f(a,x+1,y)+f(a,x,y-1)+f(a,x,y+1)+1;}}