133. Clone Graph

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 node0to both nodes1and2.
2. Second node is labeled as1. Connect node1to node2.
3. Third node is labeled as2. Connect node2to node2(itself), thus forming a self-cycle.

Visually, the graph looks like the following:

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

思路：

/**
 * 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;
        }

        LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        HashMap<UndirectedGraphNode,UndirectedGraphNode> map = 
            new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        UndirectedGraphNode newHead = new UndirectedGraphNode(node.label);

        queue.add(node);
        map.put(node,newHead);

        while(!queue.isEmpty()){
            UndirectedGraphNode curr = queue.pop();
            List<UndirectedGraphNode> currNeighbors = curr.neighbors;

            for (UndirectedGraphNode aNeighbor:currNeighbors){
                if (!map.containsKey(aNeighbor)){
                    UndirectedGraphNode copy = new UndirectedGraphNode(aNeighbor.label);
                    map.put(aNeighbor,copy);
                    map.get(curr).neighbors.add(copy);
                    queue.add(aNeighbor);
                }else{
                    map.get(curr).neighbors.add(map.get(aNeighbor));
                }
            }
        }
        return newHead;
    }
}