地、颜色、魔法(dfs)

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e6 + 10;
int n,m;
vector<char> a[maxn];
int ans;
int t,flag;
int dp[4][2] = {{0,1},{0,-1},{-1,0},{1,0}};
void dfs(int x,int y){
    t++;
    a[x][y] = ‘@‘;
    for(int i = 0; i < 4; i++) {
        int dx = x + dp[i][0],dy = y + dp[i][1];
        if (dx < 0 || dx >= n || dy < 0 || dy >= m){
            flag = 1;
            continue;
        }
        if(a[dx][dy] == ‘.‘)
            dfs(dx,dy);
    }
}
int main(){
   // freopen("in","r",stdin);
    ios::sync_with_stdio(0);
    cin >> n >> m;
    char c;
    for(int i = 0; i < n; i++){
        for(int j = 0; j < m; j++) {
            cin >> c;
            a[i].push_back(c);
        }
    }
    for(int i = 0; i < n; i++){
        for(int j = 0; j < m; j++){
            if(a[i][j] == ‘#‘)
                ans++;
            else if(a[i][j] == ‘.‘){
                flag = 0;
                t = 0;
                dfs(i,j);
                if(!flag){
                    ans += t;
                }
            }
        }
    }
    cout << ans << endl;
    return 0;
}