[LeetCode] Clone Graph

Problem:

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
         / \
         \_/

Solution:O(n)

public class Solution {
   static HashMap map = new HashMap();

   public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
      if(node == null)
         return null;
         
      UndirectedGraphNode rnode = new UndirectedGraphNode(node.label);
        
      for(UndirectedGraphNode nnode:node.neighbors){
         if(nnode != node){
            UndirectedGraphNode mynode = null;
            if(map.get(nnode)!=null ){
               mynode = map.get(nnode);
            }else{
               mynode = cloneGraph(nnode);
            }
            rnode.neighbors.add(mynode);
         }
         else{
            rnode.neighbors.add(rnode); 
         }
      }
      map.put(node, rnode);
      return rnode;
   }
}