Optimal ride (shortest route)

Idea: For the station map given in order, as in the example, 4 can go to 7 3 6, 7 can go to 3 6, and 3 can go to 6 to build a directed graph, and then find the number from point 1 to point m The shortest distance, the distance of the same question line is 1, and the question is the number of transfers, so the final answer is -1

//#pragma GCC optimize(2)
#include<bits/stdc++.h>
 
using namespace std;
typedef long long ll;
#define SIS std::ios::sync_with_stdio(false)
#define space putchar(' ')
#define enter putchar('\n')
#define lson root<<1
#define rson root<<1|1
typedef pair<int,int> PII;
const int mod=1e9+7;
const int N=1e5+5;
const int inf=0x7f7f7f7f;

int gcd(int a,int b)
{
    
    
    return b==0?a:gcd(b,a%b);
}
 
ll lcm(ll a,ll b)
{
    
    
    return a*(b/gcd(a,b));
}
 
template <class T>
void read(T &x)
{
    
    
    char c;
    bool op = 0;
    while(c = getchar(), c < '0' || c > '9')
        if(c == '-')
            op = 1;
    x = c - '0';
    while(c = getchar(), c >= '0' && c <= '9')
        x = x * 10 + c - '0';
    if(op)
        x = -x;
}
template <class T>
void write(T x)
{
    
    
    if(x < 0)
        x = -x, putchar('-');
    if(x >= 10)
         write(x / 10);
    putchar('0' + x % 10);
}
ll qsm(int a,int b,int p)
{
    
    
    ll res=1%p;
    while(b)
    {
    
    
        if(b&1)
            res=res*a%p;
        a=1ll*a*a%p;
        b>>=1;
    }
    return res;
}
int mp[2005][2005];
int dis[N];
int vis[N];
int n,m,k;
int a[N];
void dj()
{
    
    
    memset(dis,inf,sizeof dis);
   dis[1]=0;
   queue<int> q;
   q.push(1);
   while(!q.empty())
   {
    
    
       //cout<<2333<<endl;
       int now=q.front();
      // cout<<now<<endl;
       q.pop();
       for(int i=1;i<=m;i++)
       {
    
    
           if(dis[i]>dis[now]+1&&mp[now][i]!=-1)
           {
    
    
            dis[i]=dis[now]+1;
            q.push(i);
           }
       }
   }
  


}
int main()
{
    
    

     memset(mp,-1,sizeof mp);
    
      cin>>n>>m;
      string line;
      getline(cin,line);
      //cout<<line<<endl;
      while(n--)
      {
    
    
          int cnt=0;
          int x;
          getline(cin,line);
          //cout<<line<<endl;
          stringstream st(line);
          while(st>>x) a[cnt++]=x;
          for(int i=0;i<cnt;i++)
           for(int j=i+1;j<cnt;j++)
              mp[a[i]][a[j]]=1;

      }
     
         
      dj();
      if(dis[m]==inf) cout<<"NO"<<endl;
      else cout<<max(0,dis[m]-1)<<endl;
       
      

    return 0;

}