re求助

#include<bits/stdc++.h>
using namespace std;
int mp[39][39];
int n;
bool vis[39][39];
int to[4][2]={-1,0,0,1,1,0,0,-1};
struct node{
	int x,y;
};
queue<node>q;
void bfs()
{
	node u,v;
	u.x=0,u.y=0;
	q.push(u);
	vis[0][0]=1;
	mp[0][0]=-1;
	while(!q.empty())
	{
		u=q.front();
		q.pop();
		for(int i=1;i<=4;i++)
		{
			int tx=u.x+to[i][0];
			int ty=u.y+to[i][1];
			if(tx>=0&&tx<=n+1&&ty>=0&&ty<=n+1&&!vis[tx][ty]&&mp[tx][ty]==0)
			{
				v.x=tx;
				v.y=ty;
				q.push(v);
				vis[v.x][v.y]=1;
				mp[v.x][v.y]=-1;
			}
		}
	}
}
int main()
{
	cin>>n;
	for(int i=1;i<=n;i++)
		for(int j=1;j<=n;j++)
			cin>>mp[i][j];
	bfs();
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=n;j++)
		{
			if(mp[i][j]==-1)
				cout<<0<<" ";
			else if(mp[i][j]==0)
				cout<<2<<" ";
			else
				cout<<1<<" ";
		}
		cout<<endl;
	}
	return 0;
}