leetcode - Clone Graph

Nodes are labeled uniquely.

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.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
struct UndirectedGraphNode
{
	int label;
	std::vector<UndirectedGraphNode *> neighbors;
	UndirectedGraphNode(int x) : label(x) {};
};
class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
		std::unordered_map<UndirectedGraphNode*, UndirectedGraphNode *> map;
        if(node == NULL) return node;
		return dfs(node,map);
    }
private:
	UndirectedGraphNode *dfs(UndirectedGraphNode *node,std::unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> &map)
	{
		if(map.count(node) > 0) return map[node];
		UndirectedGraphNode *newNode = new UndirectedGraphNode(node->label);
		map[node] = newNode;
		for(int i = 0; i < node->neighbors.size(); i++)
		{
			newNode->neighbors.push_back(dfs(node->neighbors[i],map));
		}
		return newNode;
	}
};