HackerEarth Jungle Run problem solution

#include<bits/stdc++.h>
#define fori(z,n) for(int i=z;i<n;i++)
#define forj(z,n) for(int j=z;j<n;j++)
#define fork(z,n) for(int k=z;k<n;k++)

using namespace std;

char str[1005][1005];
bool visited[1000005];
int x[]={1,-1,0,0};
int y[]={0,0,-1,1};
int dist[1000005];
vector<int> v[1000005];
int main()
{
 //freopen("input.in", "r", stdin);
 int strt,end,n;
 cin>>n;
 fori(0,n)
 {

  forj(0,n) {
        cin>>str[i][j];
        if(str[i][j]=='S')
        {


          strt=i*n+j;
          str[i][j]='P';
        }
        if(str[i][j]=='E')
        {


            end=i*n+j;
            str[i][j]='P';
        }

  }
 }

 fori(0,n)
 {

     forj(0,n)
     {
         if(str[i][j]=='P')
         {
             if(i+1<n && str[i+1][j]=='P')
             {
             v[(i*n+j)].push_back((i+1)*n+j);
             v[((i+1)*n+j)].push_back((i)*n+j);
             }
               if(j+1<n && str[i][j+1]=='P')
             {
             v[(i*n+j)].push_back((i)*n+j+1);
             v[((i)*n+j+1)].push_back((i)*n+j);
             }
         }
     }
 }

 queue<int> q;
 for(int i=0;i<n*n;i++)
 {

    dist[i]=-1;
    visited[i]=false;
 }
 q.push(strt);
 dist[strt]=0;
 while(!q.empty())
 {
     int k=q.front();
     q.pop();
     if(!visited[k])
     {
         visited[k]=true;
         for(int i:v[k])
         {
           if(!visited[i])
           {
            q.push(i);
            if(dist[i]==-1)
                dist[i]=dist[k]+1;

           }
         }
     }
 }
 cout<<dist[end];
}