Find the Connected Component in the Undirected Graph

Find the number connected component in the undirected graph. Each node in the graph contains a label and a list of its neighbors. (a connected component (or just component) of an undirected graph is a subgraph in which any two vertices are connected to each other by paths, and which is connected to no additional vertices in the supergraph.)

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Example
Given graph:

A——B C–E
|
D
Return {A,B,D}, {C,E}. Since there are two connected component which is {A,B,D}, {C,E}

/** * Definition for Undirected graph. * class UndirectedGraphNode { *     int label; *     ArrayList<UndirectedGraphNode> neighbors; *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); } * }; */public class Solution {    /**     * @param nodes a array of Undirected graph node     * @return a connected set of a Undirected graph     */    public List<List<Integer>> connectedSet(ArrayList<UndirectedGraphNode> nodes) {        // Write your code here        if(nodes==null || nodes.size()==0)return null;     List<List<Integer>> result = new ArrayList<List<Integer>>();        Set<UndirectedGraphNode> visited = new HashSet<UndirectedGraphNode>();        for(UndirectedGraphNode node:nodes){            if(visited.contains(node)) continue;                List<Integer>    row =bfs(node,visited);            result.add(row);        }        return result;    }    private List<Integer> bfs(UndirectedGraphNode node,                Set<UndirectedGraphNode> visited){                 List<Integer>pow = new ArrayList<>();                    Queue<UndirectedGraphNode> q= new LinkedList<UndirectedGraphNode>();                    q.offer(node);                    visited.add(node);                    while(!q.isEmpty()){                        UndirectedGraphNode qnode =q.poll();                        pow.add(qnode.label);                        for(UndirectedGraphNode neighbor:qnode.neighbors){                            if(visited.contains(neighbor))continue;                                q.offer(neighbor);                                visited.add(neighbor);                        }                    }                    Collections.sort(pow);                    return pow;                }}