2.3.5.8wa

题目给的样例都输出-1；大佬帮忙看看吧

#include<bits/stdc++.h>
#define x first
#define y second
//define后面不用分号； 
//define a b 是将b定义成a；注意顺序； 
using namespace std;
typedef pair<int,int> PII;
const int N=1010;
char G[N][N];
int dist[N][N];
int n; 
queue<PII> q;
int dx[]={0,1,0,-1};
int dy[]={1,0,-1,0};
int dfs(int x1,int y1,int x2,int y2)
{
    //忘记初始化数组
    memset(dist,-1,sizeof(dist)); 

    dist[x1][y1]=0;
    q.push({x1,y1});

    while(q.size())
    {auto t=q.front();
        q.pop();

        for(int i=0;i<4;i++)
        {

            int a=t.x+dx[i];
            int b=t.y+dy[i];

         if(a<0||a>=n||b<0||b>=n)
         continue;

         if(G[a][b]=='1')
         continue;
         if(dist[a][b]>=0)
         continue;

         q.push({a,b});
         dist[a][b]=1+dist[t.x][t.y];
         if(a==x2&&b==y2)
            return dist[x2][y2];
         } 

    }
    return -1;

}
int main()
{
    cin>>n;
    int x1,x2,y1,y2;
    for(int i=0;i<n;i++)
    {
        scanf("%s",G[i]);
    }
    cin>>x1>>y1>>x2>>y2; 
    cout<<dfs(x1,y1,x2,y2);

    return 0;
 }