Clone Graph 克隆图

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.


OJ's undirected graph serialization:
Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.
As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
Second node is labeled as 1. Connect node 1 to node 2.
Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.
Visually, the graph looks like the following:

       1
      /  \
     /    \
    0 -- 2
           / \
           \_/
题目的要求是复制一个图。图中的节点有两个属性，一个是label，一个是一个邻居链表，包含着与当前节点相连的节点，换句话说就是当前节点与邻居链表中的每个点之间都有一条边。这里我们借助一个哈希表来记录当前节点和它的复制节点的对应关系。实现代码如下：

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        HashMap<UndirectedGraphNode, UndirectedGraphNode> hm = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        if(node == null) return node;
        UndirectedGraphNode copy = new UndirectedGraphNode(node.label);
        hm.put(node, copy);
        queue.offer(node);
        while(!queue.isEmpty()) {
            UndirectedGraphNode cur = queue.poll();
            for(UndirectedGraphNode neighbor : cur.neighbors) {
                if(!hm.containsKey(neighbor)) {
                    copy = new UndirectedGraphNode(neighbor.label);
                    hm.put(neighbor, copy);
                    queue.offer(neighbor);
                }
                hm.get(cur).neighbors.add(hm.get(neighbor));
            }
        }
        return hm.get(node);
    }
}