find the connected component in the undirected graph

public List<List<Integer>> connectedSet(ArrayList<UndirectedGraphNode> nodes) {
    
    List<List<Integer>> ans = new ArrayList<List<Integer>>();
    if (nodes == null || nodes.size() == 0)
        return ans;
    HashSet<UndirectedGraphNode> set = new HashSet<>();
    for (UndirectedGraphNode node : nodes) {
        if (set.contains(node))
            continue;
        Queue<UndirectedGraphNode> q = new LinkedList<>();
        List<Integer> temp = new ArrayList<>();
        q.offer(node);
        while (!q.isEmpty()) {
            UndirectedGraphNode cur = q.poll();
            if (set.contains(cur))
                continue;
            temp.add(cur.label);
            set.add(cur);
            for (UndirectedGraphNode neighbor : cur.neighbors) {
                q.offer(neighbor);
            }
        }
        // I don't understand why the OJ ask this
        Collections.sort(temp);
        ans.add(new ArrayList<Integer>(temp));
    }
    return ans;
}