A - Red and Black(3.2.1)（搜索）

6 9
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11 9
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11 6
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7 7
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45
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6
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#include<iostream>
#include<cstring>
using namespace std;
int b,c,k,i,s,x,y,n;
char a[21][21]; 
int sousuo(int x,int y,int a1,int b)
{
	int n=0;
	if(x>0)
		if(a[x-1][y]=='.')
		{n++;a[x-1][y]='a';n=n+sousuo(x-1,y,a1,b);}
    if(y>0)
		if(a[x][y-1]=='.')
		{n++;a[x][y-1]='a';n=n+sousuo(x,y-1,a1,b);}
	if(x<a1)
      if(a[x+1][y]=='.')
		{n++;a[x+1][y]='a';n=n+sousuo(x+1,y,a1,b);}
	  if(y<b)
		if(a[x][y+1]=='.')
		{n++;a[x][y+1]='a';n=n+sousuo(x,y+1,a1,b);}
		return n;
}
int main()
{
	int j;
	while(cin>>k>>s&&k)
	{
		memset(a,'q',sizeof(a));
	  for(i=0;i<s;i++)
		  for(j=0;j<k;j++)
		  {
			  cin>>a[i][j];
			  if(a[i][j]=='@')
				  x=i,y=j;
		  }

         n=sousuo(x,y,s,k);
		 cout<<++n<<endl;
	}
	return 0;
}