参考答案：

#include<iostream>
#include<string>
#include<queue>
#include<cstring>
using namespace std;
const int N = 510;
int g[N][N];
int a[N];
int dis[N];
int n, m, cnt;
string s;
int res;
void bfs()
{
    memset(dis, 0x3f, sizeof(dis));
    dis[1] = 0;
    queue<int> q;
    q.push(1);
    while (q.size())
    {
        int t = q.front();
        q.pop();
        for (int i = 1; i <= n; ++i)
        {
            if (dis[i] > dis[t] + g[t][i])
            {
                dis[i] = dis[t] + g[t][i];
                q.push(i);
            }
        }
    }
}
int main()
{
    memset(g, 0x3f, sizeof(g));
    cin >> m >> n;
    getline(cin, s);
    while (m--)
    {
        if (s.size()) s.clear();
        getline(cin, s);
        int t = 0;
        cnt = 0;
        for (int i = 0; i < s.size(); ++i)
        {
            if (s[i] != ' ') t = t * 10 + (s[i] - '0');
            else
            {
                a[cnt++] = t;
                t = 0;
            }
        }
        if (t) a[cnt++] = t;
        for (int i = 0; i < cnt; ++i)
        {
            for (int j = i + 1; j < cnt; ++j)
            {
                g[a[i]][a[j]] = 1;
            }
        }
    }
    bfs();
    if (dis[n] == 0x3f3f3f3f) cout << "NO" << endl;
    else cout << max(0, dis[n] - 1) << endl;
    return 0;
}