Clone Graph

Problem

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

How we serialize an undirected graph:

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 #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.

Second node is labeled as 1. Connect node 1 to node 2.

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
         / \
         \_/

Example

return a deep copied graph.

Code - Java

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *   int label;
 *   ArrayList<UndirectedGraphNode> neighbors;
 *   UndirectedGraphNode(int x) {
 *     label = x;
 *     neighbors = new ArrayList<UndirectedGraphNode>();
 *   }
 * };
 */
public class Solution {

    private Map<Integer, UndirectedGraphNode> map = new HashMap<>();

    /**
     * @param node: A undirected graph node
     * @return: A undirected graph node
     */
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) {
            return null;
        }
        if (map.containsKey(node.label)) {
            return map.get(node.label);
        }
        UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);
        map.put(node.label, newNode);
        for (UndirectedGraphNode neighbor : node.neighbors) {
            newNode.neighbors.add(cloneGraph(neighbor));
        }
        return newNode;
    }
}