题解 100% AC

#include <bits/stdc++.h>
using namespace std;
int n,dx[]={0,1,0,-1},dy[]={1,0,-1,0};
int a[40][40];
void dfs(int x,int y){
    a[x][y]=-1;
    for(int i=0;i<4;i++){
        int nx=x+dx[i],ny=y+dy[i];
        if(nx>=0&&ny>=0&&nx<=n+1&&ny<=n+1&&!a[nx][ny]){
            dfs(nx,ny);
        }
    }
    return;
}
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            cin>>a[i][j];
        }
    }
    dfs(0,0);
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(a[i][j]==-1) cout<<"0 ";
            else if(a[i][j]==1) cout<<"1 ";
            else if(a[i][j]==0) cout<<"2 ";
        }
        cout<<endl;
    }
    return 0;
}