克隆一張無向圖，圖中的每個節點包含一個 label （標籤）和一個 neighbors （鄰接點）列表 。

OJ的無向圖序列化：

節點被唯一標記。

我們用 # 作為每個節點的分隔符，用 , 作為節點標籤和鄰接點的分隔符。

例如，序列化無向圖 {0,1,2#1,2#2,2}。

該圖總共有三個節點, 被兩個分隔符  # 分為三部分。 

1. 第一個節點的標籤為 0，存在從節點 0 到節點 1 和節點 2
    的兩條邊。
2. 第二個節點的標籤為 1，存在從節點 1 到節點 2 的一條邊。
3. 第三個節點的標籤為 2，存在從節點 2 到節點 2 (本身) 的一條邊，從而形成自環。

我們將圖形視覺化如下：

       1
      / \
     /   \
    0 --- 2
         / \
         \_/

/**
 * 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) {
        if(node == null) return null;
        HashMap<UndirectedGraphNode,UndirectedGraphNode> hashMap = new HashMap<>();
        LinkedList<UndirectedGraphNode> queue = new LinkedList<>();
        UndirectedGraphNode head = new UndirectedGraphNode(node.label);
        hashMap.put(node,head);
        queue.offer(node);
        while(!queue.isEmpty()){
            UndirectedGraphNode curNode = queue.poll();
            for(UndirectedGraphNode neighbor:curNode.neighbors){
                if(hashMap.containsKey(neighbor)==false){
                    queue.offer(neighbor);
                    UndirectedGraphNode newNeighbor = new UndirectedGraphNode(neighbor.label);
                    hashMap.put(neighbor,newNeighbor);
                }
                hashMap.get(curNode).neighbors.add(hashMap.get(neighbor));
            }
        }
        return head;
    }
}
 

public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {//DFS
        if (node == null) return null;
        HashMap<UndirectedGraphNode, UndirectedGraphNode> hashMap = new HashMap<>();
        UndirectedGraphNode head = new UndirectedGraphNode(node.label);
        hashMap.put(node, head);
        DFSSearch(hashMap, node);
        return head;
    }

    private void DFSSearch(HashMap<UndirectedGraphNode, UndirectedGraphNode> hashMap, UndirectedGraphNode node) {
        if (node == null) return;
        for (UndirectedGraphNode neighbor : node.neighbors) {
            if (hashMap.containsKey(neighbor) == false) {
                UndirectedGraphNode newNeighbor = new UndirectedGraphNode(neighbor.label);
                hashMap.put(neighbor, newNeighbor);
                DFSSearch(hashMap, neighbor);
            }
            hashMap.get(node).neighbors.add(hashMap.get(neighbor));
        }
    }。
 

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    map<int,UndirectedGraphNode*> A;
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(!node) return NULL;
        UndirectedGraphNode *p = new UndirectedGraphNode(node->label);
        A[node->label] = p;
        for(auto &x:node->neighbors)
            if(!A.count(x->label)) p->neighbors.push_back(cloneGraph(x));
            else p->neighbors.push_back(A[x->label]);
        return p;
    }
};