dfs求树的最大层次+所有最远叶节点

import java.util.*;

public class Main {
    static int N = 100010;
    static int[] e = new int[N * 2];
    static int[] ne = new int[N * 2];
    static int[] h = new int[N];
    static int idx;
    static int n;
    static int start;
    static int level;
    static int max = -1;
    static List<Integer> list = new ArrayList<>();

    public static void add(int a,int b) {
        e[idx] = b;
        ne[idx] = h[a];
        h[a] = idx ++;
    }
    public static void dfs(int begin,int level) {
        if (level == max) {
            list.add(begin);
        }
        if (level > max) {
            list.clear();
            max = level;
            list.add(begin);
        }
        for (int i = h[begin];i != -1;i = ne[i]) {
            int j = e[i];
            if (j != begin)
                dfs(j,level+1);
        }
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();

        Arrays.fill(h,-1);

        for (int i = 1;i <= n;i ++) {
            int x = sc.nextInt();
            if (x == -1) {
                start = i;
                continue;
            }
            add(x,i);
        }
        dfs(start,1);

        System.out.println(max);

        Collections.sort(list);
        int j = 1;
        for (int i:list) {
            if (j != list.size()) {
                System.out.print(i + " ");
            } else {
                System.out.print(i);
            }
            j ++;
        }
    }
}