leetcode 133. Clone Graph ----- java

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

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
         / 
         \_/

 复制图。有DFS和BFS两种方法，我选用了BFS的方法。

/**
 * 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;

        Map map = new HashMap<Integer,UndirectedGraphNode>();
        Queue queue = new LinkedList<UndirectedGraphNode>();

        queue.add(node);
        UndirectedGraphNode nnn = new UndirectedGraphNode(node.label);
        map.put(nnn.label,nnn);

        while( !queue.isEmpty() ){
            UndirectedGraphNode nn = (UndirectedGraphNode) queue.poll();

            List ll1 = nn.neighbors;
            UndirectedGraphNode nn2 = (UndirectedGraphNode) map.get(nn.label);
            List ll2 = nn2.neighbors;

            for( int i = 0;i<ll1.size();i++){

                UndirectedGraphNode node2 = (UndirectedGraphNode) ll1.get(i);
                if( map.containsKey(node2.label) ){
                    ll2.add(map.get(node2.label));
                }else{
                    UndirectedGraphNode node3 = new UndirectedGraphNode(node2.label);
                    map.put(node2.label,node3);
                    ll2.add(node3);
                    queue.add(node2);
                }
            }

        }
        
    return nnn;}
}