LeetCode: Clone Graph

public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        Queue<UndirectedGraphNode> nodes = new LinkedList<UndirectedGraphNode>();
        if (node == null) return node;
        
        UndirectedGraphNode head = new UndirectedGraphNode(node.label);
        map.put(node, head);
        nodes.add(node);
            
        while (!nodes.isEmpty()) {
            UndirectedGraphNode org = nodes.poll();
            UndirectedGraphNode k = map.get(org);
            for (UndirectedGraphNode t : org.neighbors) {
                UndirectedGraphNode n;
                if (!map.containsKey(t)) {
                    n = new UndirectedGraphNode(t.label);
                    map.put(t, n);
                    nodes.add(t);//如果这是一个新的node，需要将其放入队列中，准备将其neighbors赋值。
                }
                else {
                    n = map.get(t);
　　　　　　　　　　　　　//这里不再需要放入队列中，因为这个节点已经存在，说明它一定被创建过，一定也就被放入到队列中过。
                }
                k.neighbors.add(n);
            }
        }
        return head;
    }
}