Clone an undirected graph. Each node in the graph contains alabeland a list of itsneighbors.

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#.

1. First node is labeled as 0 . Connect node 0 to both nodes 1 and 2 .
2. Second node is labeled as 1 . Connect node 1 to node 2 .
3. 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
         / \
         \_/

Answer:https://leetcode.com/problems/clone-graph/description/#

/**
 * Definition for undirected graph.
 * public class UndirectedGraphNode {
 *     public int label;
 *     public IList<UndirectedGraphNode> neighbors;
 *     public UndirectedGraphNode(int x) { label = x; neighbors = new List<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode CloneGraph(UndirectedGraphNode node) {
     if (node == null)
        {
            return node;
        }

        // use bfs algorithm to traverse the graph and get all nodes.
        List<UndirectedGraphNode> nodes = getNodes(node);

        // copy nodes, store the old->new mapping information in a hash map
        Dictionary<UndirectedGraphNode, UndirectedGraphNode> mapping = new Dictionary<UndirectedGraphNode, UndirectedGraphNode>();
        foreach (UndirectedGraphNode n in nodes)
        {
            mapping[n] = new UndirectedGraphNode(n.label);
        }

        // copy neighbors(edges)
        foreach (UndirectedGraphNode n in nodes)
        {
            UndirectedGraphNode newNode = mapping[n];
            foreach (UndirectedGraphNode neighbor in n.neighbors)
            {
                UndirectedGraphNode newNeighbor = mapping[neighbor];
                newNode.neighbors.Add(newNeighbor);
            }
        }

        return mapping[node];
    }

    private List<UndirectedGraphNode> getNodes(UndirectedGraphNode node)
    {
        Queue<UndirectedGraphNode> queue = new Queue<UndirectedGraphNode>();
        HashSet<UndirectedGraphNode> set = new HashSet<UndirectedGraphNode>();

        queue.Enqueue(node);
        set.Add(node);
        while (queue.Count > 0)
        {            
            UndirectedGraphNode head = queue.Dequeue();
            foreach (UndirectedGraphNode neighbor in head.neighbors)
            {
                if (!set.Contains(neighbor))
                {
                    set.Add(neighbor);
                    queue.Enqueue(neighbor);
                }
            }
        }

        return new List<UndirectedGraphNode>(set); //or set.ToList()
    }
}