我写了这道题目蛮久的,谁知道是水题



Problem Description
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.
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)
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)
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
#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
char G[25][25];
bool vist[25][25];
int m,n,co;
int dir[4][2]={{0,-1},{0,1},{-1,0},{1,0}};
void dfs(int x,int y){
co++;
vist[x][y]=1;
for(int i=0;i<4;i++){
int x1=x+dir[i][0];
int y1=y+dir[i][1];
if(x1>=0 && x1<m && y1>=0 && y1<n){
if(G[x1][y1]=='.'&&!vist[x1][y1])
{
dfs(x1,y1);
vist[x1][y1]=1;
}
}
}
}
int main()
{
int i,j,a,b;
while(cin>>n>>m) //n为列,m为行
{
if(n==0&&m==0)
break;
memset(vist,0,sizeof(vist));
for(i=0;i<m;i++)
{
cin>>G[i];
}
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
if(G[i][j]=='@')
{
a=i;
b=j;
}
}
}
co=0;
dfs(a,b);
cout<<co<<endl;
}
return 0;
}