求助！70分，第4，5，7个测试点没过

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int n,s1,s2,s3,s4;
int biao[1001][1001];
char arr[1001][1001];
bool mark[1001][1001];
pair<int,int>dui[1001*1001];
int x1[4]={1,-1,0,0};
int y1[4]={0,0,1,-1};
int bfs(pair<int,int>s){
    int begin=0,over=0;
    dui[begin++]=s;
    while(begin>over){
        pair<int,int>h=dui[over++];
        for(int i=0;i<4;i++){
            int x=h.first+x1[i],y=h.second+y1[i];
            if(x<1||x>n||y<1||y>n)continue;
            if(mark[x][y])continue;
            if(arr[x][y]=='1')continue;
            biao[x][y]=biao[h.first][h.second]+1;
            if(x==s3&&y==s4)return biao[x][y];
            mark[x][y]=1;
            dui[begin++]=make_pair(x,y);
        }
    }
}
int main(){
cin>>n;
for(int i=1;i<=n;i++)cin>>arr[i];
cin>>s1>>s2>>s3>>s4;
cout<<bfs(make_pair(s1,s2));
return 0; 
}