CloneGraph

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

OJ's undirected graph serialization:

Nodes are labeled from 0 to N - 1, where N is the total nodes in the graph.

We use # as a separator for each node, and , as a separator for each neighbor of the node.

As an example, consider the serialized graph {1,2#2#2}.

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

1. Connect node 0 to both nodes 1 and2.
2. Connect node 1 to node 2.
3. Connect node 2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:

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

BFS solution. 通过hashtable来记录是否已经创建clone node

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     ArrayList<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
import java.util.Hashtable;
public class Solution {
	public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
		// Note: The Solution object is instantiated only once and is reused by
		// each test case.
		if (node == null)
			return null;
		Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
		queue.add(node);
		Hashtable<UndirectedGraphNode, UndirectedGraphNode> hashtable = new Hashtable<UndirectedGraphNode, UndirectedGraphNode>();
		UndirectedGraphNode node_copy = new UndirectedGraphNode(node.label);
		hashtable.put(node, node_copy);
		while (!queue.isEmpty()) {
			UndirectedGraphNode cur = queue.poll();
			for (UndirectedGraphNode neighbor : cur.neighbors) {
				if (!hashtable.containsKey(neighbor)) {
					UndirectedGraphNode neighbor_copy = new UndirectedGraphNode(
							neighbor.label);
					hashtable.get(cur).neighbors.add(neighbor_copy);
					hashtable.put(neighbor, neighbor_copy);
					queue.add(neighbor);
				} else {
					hashtable.get(cur).neighbors.add(hashtable.get(neighbor));
				}
			}
		}
		return node_copy;
	}

}