Clone Graph

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
         / \
         \_/

 /**
  * 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;

         ArrayList<UndirectedGraphNode> nodes = new ArrayList<>();
         HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();

         // clone nodes
         nodes.add(node);
         map.put(node, new UndirectedGraphNode(node.label));

         int start = ;
         while (start < nodes.size()) {
             UndirectedGraphNode head = nodes.get(start++);
             for (UndirectedGraphNode neighbor : head.neighbors) {
                 if (!map.containsKey(neighbor)) {
                     map.put(neighbor, new UndirectedGraphNode(neighbor.label));
                     nodes.add(neighbor);
                 }
             }
         }

         // clone neighbors
         for (UndirectedGraphNode originalNode : nodes) {
             UndirectedGraphNode copyNode = map.get(originalNode);
             for (UndirectedGraphNode neighbor : originalNode.neighbors) {
                 copyNode.neighbors.add(map.get(neighbor));
             }
         }

         return map.get(node);
     }
 }