Clone Graph

这里使用BFS来解本题，BFS需要使用queue来保存neighbors

但这里有个问题，在clone一个节点时我们需要clone它的neighbors，而邻居节点有的已经存在，有的未存在，如何进行区分？

这里我们使用Map来进行区分，Map的key值为原来的node，value为新clone的node，当发现一个node未在map中时说明这个node还未被clone，

http://oj.leetcode.com/problems/clone-graph/

    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if(node==null)
            return null;
        UndirectedGraphNode copyroot=new UndirectedGraphNode(node.label);
        UndirectedGraphNode copyfollow=copyroot;
        UndirectedGraphNode follow=node;
        
        Queue<UndirectedGraphNode> queue=new LinkedList();
        HashMap<UndirectedGraphNode,UndirectedGraphNode> copyHash=new HashMap<UndirectedGraphNode,UndirectedGraphNode>();
        queue.add(follow);
        copyHash.put(follow, copyfollow);
        while(queue.isEmpty()==false)
        {
            UndirectedGraphNode p=queue.poll();
            copyfollow=copyHash.get(p);
            if(p.neighbors!=null)
                copyfollow.neighbors=new ArrayList<UndirectedGraphNode>();
            for(UndirectedGraphNode elem:p.neighbors)
            {
                if(copyHash.containsKey(elem))
                {
                    copyfollow.neighbors.add(copyHash.get(elem));
                }
                else
                {
                    queue.add(elem);
                    UndirectedGraphNode temp=new UndirectedGraphNode(elem.label);
                    temp.neighbors=null;
                    copyfollow.neighbors.add(temp);
                    copyHash.put(elem, temp);
                }
            }
        }
        return copyroot;
    }