简单易懂超暴力
第九届蓝桥杯第九题

#include<bits/stdc++.h>
using namespace std;

const int maxn = 1005;
char mp[maxn][maxn];
int vis[maxn][maxn];
int ans[100005];
int n;

void dfs(int x, int y, int cnt) {
  if (x < 0 || y < 0 || x >= n|| y >= n)
    return;

  if (vis[x][y])
    return;

  if (mp[x][y] == '.')
    return;

  vis[x][y] = 1;

  if (mp[x-1][y] == '#' && mp[x+1][y] == '#' && mp[x][y-1] == '#' && mp[x][y+1] == '#')
    ans[cnt]++;

  dfs(x-1,y,cnt);
  dfs(x+1,y,cnt);
  dfs(x,y-1,cnt);
  dfs(x,y+1,cnt);
}

int main() 
{
  scanf("%d", &n);

  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++)
      cin>>mp[i][j];

  int len = 0;

  for (int i = 0; i < n; i++) {
    for (int j=0; j<n; j++) {
      if(mp[i][j] == '#' &&  !vis[i][j]) {
        dfs(i, j, len);
        len ++;
      }
    }
  }

  int sum = 0;
  for (int i = 0; i < len; i++)
    if (ans[i] == 0) sum++;
  cout << sum << endl;
}