leetcode: 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.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        
        UndirectedGraphNode *retNode = NULL;
        map<UndirectedGraphNode*, UndirectedGraphNode*> nodeMap;
        list<UndirectedGraphNode *> nodeList;
        
        if (node == NULL)
            return NULL;
        
        nodeList.push_back(node);
        
        retNode = new UndirectedGraphNode(node->label);
        nodeMap[node] = retNode;
        
        while (nodeList.size() > 0)
        {
            UndirectedGraphNode *curNode = nodeList.front();
            UndirectedGraphNode *clonedNode = nodeMap[curNode];
            nodeList.pop_front();
        
            for (int i=0; i<curNode->neighbors.size(); i++)
            {
                UndirectedGraphNode *oldNeighborNode = curNode->neighbors[i];
                
                if (nodeMap.find(oldNeighborNode) == nodeMap.end())
                {
                    UndirectedGraphNode *newNeighborNode = new UndirectedGraphNode(oldNeighborNode->label);
                    nodeList.push_back(oldNeighborNode);
                    nodeMap[oldNeighborNode] = newNeighborNode;
                }
                
                clonedNode->neighbors.push_back(nodeMap[oldNeighborNode]);
            }
        }
        return retNode;
    }
};