算法1:dfs
#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
const int N=25;
char g[N][N];
bool vis[N][N];
int n,m,sx,sy;
int dx[]={0,1,0,-1},dy[]={-1,0,1,0};
int dfs(int x,int y){
int cnt=1;
vis[x][y]=true;
for(int i=0;i<4;++i){
int a=x+dx[i],b=y+dy[i];
if(a<0||a>=n||b<0||b>=m) continue;
if(g[a][b]!='.') continue;
if(vis[a][b]) continue;
cnt+=dfs(a,b);
}
return cnt;
}
int main(){
while(cin>>m>>n,n||m){
memset(vis,0,sizeof vis);
for(int i=0;i<n;i++) cin>>g[i];
for(int i=0;i<n;i++){
for(int j=0;j<m;j++){
if(g[i][j]=='@'){
sx=i,sy=j;
}
}
}
cout<<dfs(sx,sy)<<endl;
}
return 0;
}
算法2:bfs
#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
const int N=25;
char g[N][N];
bool vis[N][N];
int n,m,sx,sy;
int dx[]={0,1,0,-1},dy[]={-1,0,1,0};
int bfs(int x,int y){
int res=1;
vis[x][y]=true;
queue<pair<int,int> > q;
q.push({x,y});
while(q.size()){
pair<int,int> now=q.front(); q.pop();
for(int i=0;i<4;i++){
int ex=now.first+dx[i],ey=now.second+dy[i];
if(ex>=0&&ex<n&&ey>=0&&ey<m&&g[ex][ey]=='.'&&!vis[ex][ey]){
vis[ex][ey]=true;
res++;
q.push({ex,ey});
}
}
}
return res;
}
int main(){
while(cin>>m>>n,n||m){
memset(vis,0,sizeof vis);
for(int i=0;i<n;i++) cin>>g[i];
for(int i=0;i<n;i++){
for(int j=0;j<m;j++){
if(g[i][j]=='@'){
sx=i,sy=j;
}
}
}
cout<<bfs(sx,sy)<<endl;
}
return 0;
}