#include <bits/stdc++.h>
#define x first
#define y second
using namespace std;
typedef pair<int,int>PII;
queue<PII> q;
const int N=1010; 
int n;
char g[N][N];
int dist[N][N];
int dx[]={-1,0,1,0};
int dy[]={0,1,0,-1};
int ans,res;
int bfs(int x1,int y1){
    int cnt1=0;
    q.push({x1,y1});
    dist[x1][y1]=0;
    for(int i=0;i<4;i++){
        int w=x1+dx[i],z=y1+dy[i];
        if(w<1||w>n||z<1||z>n) continue;
        if(g[w][z]=='#') cnt1++;
    }
    if(cnt1==4) res++;
    
    while(q.size()){
        auto t=q.front();
        q.pop();
        for(int i=0;i<4;i++){
            int a=t.x+dx[i],b=t.y+dy[i];
            if(a<1||a>n||b<1||b>n) continue;
            if(g[a][b]!='#') continue;
            if(dist[a][b]>=0) continue;
            
            q.push({a,b});
            dist[a][b]=dist[t.x][t.y]+1;
            int cnt2=0;
            for(int i=0;i<4;i++){
                int w=a+dx[i],z=b+dy[i];
                if(w<1||w>n||z<1||z>n) continue;
                if(g[w][z]=='#') cnt2++;
            }
            if(cnt2==4) res++;
        }
    }
} 
int main() {
    memset(dist,-1,sizeof(dist));
    cin>>n;
    for(int i=1;i<n;i++){
        for(int j=1;j<=n;j++){
            cin>>g[i][j];
        }
    }
    for(int i=1;i<n;i++){
        for(int j=1;j<=n;j++){
            if(g[i][j]=='#'&&dist[i][j]==-1){
                bfs(i,j);
                ans++;//岛屿数量 
            }
        }
    }
    cout<<ans-res;
    return 0;
}

为什么全都RE了呢,能过样例