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 #.

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
     / \
     \_/

Solution

/**
 * 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<Integer, UndirectedGraphNode> map = new HashMap<>();
        cloneNode(map, node);
        return map.get(node.label);
    }

    public void cloneNode(Map<Integer, UndirectedGraphNode> map, UndirectedGraphNode node) {
        int currentLabel = node.label;
        if (!map.containsKey(currentLabel)) {
            map.put(currentLabel, new UndirectedGraphNode(currentLabel));
        }

        UndirectedGraphNode clone = map.get(currentLabel);
        for(UndirectedGraphNode n: node.neighbors) {
            if (!map.containsKey(n.label)) {
                map.put(n.label, new UndirectedGraphNode(n.label));
                cloneNode(map, n);
            }

            clone.neighbors.add(map.get(n.label));
        }

    }
}