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
         / \
         \_/

tag: BFS

/**
 * 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;

        //1. get all nodes
        Set<UndirectedGraphNode> nodes = getNodes(node);

        Map<UndirectedGraphNode, UndirectedGraphNode> hash = new HashMap<>();
        //2. construct map
        for (UndirectedGraphNode n : nodes){
            hash.put(n, new UndirectedGraphNode(n.label));
        }

        //3. handle neighbors
        for (UndirectedGraphNode n : nodes){
            for (UndirectedGraphNode neighbor : n.neighbors){
                hash.get(n).neighbors.add(hash.get(neighbor));
            }
        }

        return hash.get(node);
    }

    private Set<UndirectedGraphNode> getNodes(UndirectedGraphNode node){
        Set<UndirectedGraphNode> ans = new HashSet<>();
        Queue<UndirectedGraphNode> q = new LinkedList<>();

        q.offer(node);
        ans.add(node);

        while (!q.isEmpty()){
            UndirectedGraphNode cur = q.poll();

            for (UndirectedGraphNode neighbor : cur.neighbors){
                if (ans.contains(neighbor)) continue;

                q.offer(neighbor);
                ans.add(neighbor);
            }
        }

        return ans;
    }
}