problem

solution

codes

#include<iostream>
#include<queue>
using namespace std;
struct xyz{
    int x, y;
    xyz(int x = 0, int y = 0):x(x),y(y){};
};
int n, m, ans;
char a[2010][2010];
const int dx[] = {0,0,-1,1};
const int dy[] = {-1,1,0,0};
void bfs(int x, int y){
    queue<xyz>q;
    q.push(xyz(x,y));
    a[x][y] = '#';
    while(!q.empty()){
        xyz t = q.front(); q.pop();
        for(int i = 0; i < 4; i++){
            int newx = t.x+dx[i], newy = t.y+dy[i];
            if(newx>=0 && newx<n && newy>=0 && newy<m && a[newx][newy]=='.'){
                q.push(xyz(newx, newy));
                a[newx][newy] = '#';
            }
        }
    }
}
int main(){
    cin>>n>>m;  //cin.get();
    for(int i = 0; i < n; i++)
        for(int j = 0; j < m; j++)
            cin>>a[i][j];
    for(int i = 0; i < n; i++)
        for(int j = 0; j < m; j++)
            if(a[i][j] == '.'){ bfs(i,j); ans++;}
    cout<<ans<<"\n";
    return 0;
}