Solution for "Important Stops"

import algorithms.*;
import java.util.*;

class Main {
  static ArrayList<ArrayList<Integer>> g;
  static int m, n;

  public static void main(String[] args) {
      // Uncomment this line if you want to read from a file
      In.open("diff/test1.in");
      Out.compareTo("diff/test1.out");

      int t = In.readInt();
      for (int i = 0; i < t; i++) {
          testCase();
      }

      In.close();
  }

  public static void testCase() {
      // Input using In.java class
      n = In.readInt();
      m = In.readInt();

      g = new ArrayList<>();

      for (int i = 0; i < n; i++) {
        g.add(new ArrayList<>());
      }

      for (int i = 0; i < m; i++) {
        int u = In.readInt();
        int v = In.readInt();
        g.get(u).add(v);
        g.get(v).add(u);
      }

      int ZHKs = countZHK(-1);

      String result = "";

      for (int i = 0; i < n; i++) {
        if (countZHK(i) > ZHKs) {
          result += String.format("%d ",i);
        }
      }

      Out.println(result.equals("") ? -1 : result);
  }

  public static int countZHK(int without) {
    boolean[] vis = new boolean[n];
    int ZHKs = 0;

    for (int i = 0; i < n; i++) {
      if (!vis[i] && i != without) {
        ZHKs++;
        DFS(i, vis, without);
      }
    }

    return ZHKs;
  }

  public static void DFS(int v, boolean[] vis, int without) {
    vis[v] = true;

    for (int u : g.get(v)) {
      if (u != without && !vis[u]) {
        DFS(u, vis, without);
      }
    }
  }
}