June 2019 b multi-layer joint training school - wide search algorithm Problem A rescue search

Wide search of water problem, I do not say it, review the wide search

#include<bits/stdc++.h>
using namespace std;
const int N=1550;
const int maxn=1e6+7;
int n;
int xx,yy,x,y;
char ditu[N][N];
int fx[5]={0,0,1,0,-1};
int fy[5]={0,1,0,-1,0};
int a[maxn][4];
bool vis[N][N]; 
bool can[N][N];
int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=n;j++)
        {
            cin>>ditu[i][j];
            if(ditu[i][j]=='0')    can[i][j]=true;
        }
    }
    cin>>x>>y>>xx>>yy;
    int t=0,w=1;
    vis[x][y]=true; 
    a[1][1]=x;
    a[1][2]=y;
    a[1][3]=0;
    while(t<w)
    {
        t++;
        for(int i=1;i<=4;i++)
        {
            int dx=a[t][1]+fx[i];
            int dy=a[t][2]+fy[i];
            if(dx>0&&dy>0&&dx<=n&&dy<=n&&!vis[dx][dy]&&can[dx][dy])
            {
                w++;
                vis[dx][dy]=true;
                a[w][1]=dx;
                a[w][2]=dy;
                a[w][3]=a[t][3]+1;
                if(dx==xx&&dy==yy)
                {
                    printf("%d",a[w][3]);
                    return 0;
                }
            }
        }
    }
    return 0;
}