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 C (judge verdict: Time Limit Exceeded)

#include <stdio.h>

#define MAPX 25
#define MAPY 25
char data[MAPY][MAPX];
int h,w;
int search(int num, int nowx, int nowy){
	num = 1;
	data[nowy][nowx] = '#';
	if(nowx>0   && data[nowy][nowx-1]=='.')num += search(num, nowx-1, nowy);
	if(nowy>0   && data[nowy-1][nowx]=='.')num += search(num, nowx, nowy-1);
	if(nowx<w-1 && data[nowy][nowx+1]=='.')num += search(num, nowx+1, nowy);
	if(nowy<h-1 && data[nowy+1][nowx]=='.')num += search(num, nowx, nowy+1);
	return num;
}

void solve(){
	int i,t;
	int sx,sy;
	for(i = 0;i < h;i++)
		scanf("%s", data[i]);
	for(i = 0;i < h;i++){
		for(t = 0;t < w;t++){
			if(data[i][t]=='@'){
				sx = i;
				sy = t;
			}
		}
	}
	printf("%d\n", search(0,  sx, sy));
}

int main(){
	while(1){
		scanf("%d %d", &h, &w);
		if(h == 0 && w == 0)break;
		solve(h,w);
	}
	return 0;
}