題目：
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 0Sample Output
45 59 6 13
AC CODE
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn = 25;
int m,n,ans;
char s[maxn][maxn];
int v[maxn][maxn];
int dx[]={1,-1,0,0}, dy[]={0,0,1,-1};
int dfs(int x,int y)
{
if(x<0 || y<0 ||x>=n ||y>=m || s[x][y] == '#' || v[x][y]!=0 ) return 0;
v[x][y] = 1;
ans++;
for(int i=0; i<4; i++)
dfs(x+dx[i], y+dy[i]);
return ans;
}
int main()
{
while(~scanf("%d%d",&m,&n)&&(m+n))
{
ans=0;
memset(v,0,sizeof(v));
for(int i=0; i<n; i++)
cin>>s[i];
for(int i=0;i<n;i++)
for(int j=0; j<m; j++)
if(s[i][j]=='@'&&v[i][j]==0) dfs(i,j);
cout<<ans<<endl;
}
return 0;
}