dfs求最长+路径记录（数组son记录）+路径比较

import java.util.*;

public class Main {
    static int N = 10010;
    static int root;
    static int[] e = new int[N];
    static int[] ne = new int[N];
    static int[] h = new int[N];
    static boolean[] st = new boolean[N];
    static int idx;
    static int[] son = new int[N];//当前节点的下一个节点

    public static void add(int a,int b) {
        e[idx] = b;
        ne[idx] = h[a];
        h[a] = idx ++;
    }
    public static int dfs(int u) { //返回深度
        int maxlen = 0;
        for (int i = h[u];i != -1;i = ne[i]) {
            int j = e[i];
            int len = dfs(j);
            if (len > maxlen) {
                maxlen = len;
                son[u] = j;
            } else if (len == maxlen) {
                son[u] = Math.min(son[u],j);
            }
        }
        return maxlen + 1;
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        Arrays.fill(h,-1);
        Arrays.fill(son,-1);

        for (int i = 0;i < n;i ++) {
            int k = sc.nextInt();
            while (k -- > 0) {
                int x = sc.nextInt();
                st[x] = true;
                add(i,x);
            }
        }
        //找树的根节点
        for (int i = 0;i < n;i ++) {
            if (!st[i])
                root = i;
        }
        System.out.println(dfs(root));

        System.out.print(root);
        for (int i = son[root];i != -1;i = son[i])
            System.out.print(" " + i);
    }
}