DFS思路觉得没问题，但是只过了三个点，求助大佬

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int N = 1002;
int n, ans;
char c;
int map[N][N];
bool st[N][N];
int dx[4] = { 0,0,1,-1 };
int dy[4] = { 1,-1,0,0 };
void dfs(int x1, int y1)
{
    st[x1][y1] = 1;
    for (int k = 0; k < 4; k++)
    {
        int x = x1 + dx[k], y = y1 + dy[k];
        if (!st[x][y] && map[x][y] == 1 && x >= 1 && x <= n && y >= 1 && y <= n)
            dfs(x, y);
    }
}
int main()
{
    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
        {
            cin >> c;
            map[i][j] = (c == '#');
        }
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            if (!st[i][j] && map[i][j])
            {
                ans++;
                dfs(i, j);
            }

    memset(st, 0, sizeof st);
    for (int i = 0; i <= n + 1; i++)
    {
        map[0][i] = 1;
        map[i][0] = 1;
        map[n + 1][0] = 1;
        map[0][n + 1] = 1;
    }
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            if (map[i][j] == 1)
            {
                for (int k = 0; k < 4; k++)
                {
                    int x = i + dx[k], y = j + dy[k];
                    if (x >= 1 && x <= n && y >= 1 && y <= n && map[x][y] == 0)map[i][j] = 2;
                }
            }
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            if (!st[i][j] && map[i][j] == 1)
            {
                ans--;
                dfs(i, j);
            }
    printf("%d", ans);
    return 0;
}