蒟蒻12分求助

#include<iostream>
#include<queue>
using namespace std;
char a[1000][1000], b[1000][1000], vis[1000][1000];
int n, s=0;
struct pos{
    int x, y;
    pos (int ax, int ay){
        x=ax, y=ay;
    }
};
void bfs(int x, int y){
    queue <pos> q;
    q.push(pos(x, y));
    while(!q.empty()){
        pos now=q.front();
        q.pop();
        int x=now.x, y=now.y;
        if(x<1||x>n||y<1||y>n||vis[x][y]||b[x][y]=='.')continue;
        vis[x][y]=1;
        q.push(pos(x+1, y));
        q.push(pos(x, y+1));
        q.push(pos(x, y-1));
        q.push(pos(x-1, y));
    }
}
int main(){
    cin>>n;
    for(int i=0;i<=n+1;i++){    
        for(int j=0;j<=n+1;j++){
        a[i][j]='#';
        }
    }
    for(int i=1;i<=n;i++){  
    for(int j=1;j<=n;j++){
        cin>>a[i][j];
    }
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(a[i+1][j]=='.'||a[i][j+1]=='.'||a[i-1][j]=='.'||a[i][j-1]=='.'||a[i][j]=='.'){
                b[i][j]='.';
            }
            else b[i][j]='#';
        }
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(vis[i][j]==0&&b[i][j]=='#'){
                bfs(i, j);
                s++;
            }
        }
    }
    cout<<s;
    return 0;
}