c++MLE，就对了第二个数据，求助:(

#include<iostream>
#include<cstdio>
#include<cmath>
#include<queue>
#include<cstdlib>
using namespace std;

int n;
int map[1005][1005];
char a[1005][1005];
int x11,y11,x22,y22;
int dx[]={0,0,1,-1};
int dy[]={1,-1,0,0};
bool vis[1005][1005];

struct node
{
    int x,y,count;
}fir;

queue <node>q;

int main()
{
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=n;j++)
        {
            cin>>a[i][j];
            map[i][j]=a[i][j]-'0';
        }
    }
    cin>>x11>>y11>>x22>>y22;
    fir.x=x11;
    fir.y=y11;
    vis[x11][y11]=1;
    fir.count=0;
    q.push(fir);
    struct node top;
    while(q.empty()==0)
    {
        top=q.front();//cout<<top.x<<" "<<top.y<<endl;
        q.pop();
        if(top.x==x22&&top.y==y22)goto what;

        for(int i=0;i<4;i++)
        {
            struct node nxt;
            nxt.x=top.x+dx[i];
            nxt.y=top.y+dy[i];
            if(nxt.x<1||nxt.x>n||nxt.y<1||nxt.y>n) continue;
            if(map[nxt.x][nxt.y]==1)continue;
            if(vis[nxt.x][nxt.y]==1)continue;
            nxt.count=top.count+1;
            vis[top.x][top.y]=1;
            q.push(nxt);
        }
    }
    what:
        cout<<top.count;
    return 0;
}