思路：

• 求所有边权为1的单源最短路 (BFS,Dijkstra,spfa)
• 难点：建图
• 理解题意 何为换乘

spfa

import java.io.*;
import java.util.*;

public class Main{
    private static int N = 1000;
    private static int n,m,idx,INF = 0x3f3f3f3f;
    private static int[] h,e,ne;
    private static boolean[] st = new boolean[N];
    private static int[] dist = new int[N];

    private static void add(int a,int b){
        e[idx] = b;
        ne[idx] = h[a];
        h[a] = idx++;
    }

    private static int spfa(){
        Arrays.fill(dist,INF);
        dist[1] = 0;
        Queue<Integer> que = new LinkedList<>();
        que.offer(1);
        st[1] = true;
        while(!que.isEmpty()){
            int t = que.poll();
            st[t] = false;
            for(int i = h[t] ; i != -1 ; i = ne[i]){
                int j = e[i];
                if(dist[j] > dist[t] + 1){
                    dist[j] = dist[t] + 1;
                    if(!st[j]){
                        que.offer(j);
                        st[j] = true;
                    }
                }
            }
        }
        if(dist[n] == INF) return -1;
        return dist[n]-1;
    }
    public static void main(String[] args)throws IOException{
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String[] s = in.readLine().split("\\s+");
        m = Integer.valueOf(s[0]);
        n = Integer.valueOf(s[1]);
        h = new int[N];e = new int[N];ne = new int[N];
        Arrays.fill(h,-1);
        while(m-->0){
            s = in.readLine().split("\\s+");
            for(int i = 0 ; i < s.length-1 ; i++){
                int a = Integer.valueOf(s[i]);
                for(int j = i +1 ; j < s.length ; j++){
                    int b = Integer.valueOf(s[j]);
                    add(a,b);
                }
            }
        }
        int ans = spfa();
        if(ans == -1) System.out.println("NO");
        else System.out.println(ans);
    }
}