Clone Graph [LeetCode]

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
         / 
         \_/

Summary: BFS, one queue for BFS, one map for visited nodes,  one map for mapping between original nodes and the nodes of new graph.

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(node == NULL)
            return NULL;
        vector<UndirectedGraphNode *> node_queue;
        map<UndirectedGraphNode *, bool> visited;
        map<UndirectedGraphNode *, UndirectedGraphNode *> node_map;
        UndirectedGraphNode * root = new UndirectedGraphNode(node->label);
        node_map[node] = root;
        visited[node] = true;
        node_queue.push_back(node);
        
        while(node_queue.size() > 0){
            UndirectedGraphNode * node = node_queue[0];
            node_queue.erase(node_queue.begin());
            UndirectedGraphNode * new_node = node_map[node];
            for(auto item : node->neighbors){
                if(visited.find(item) != visited.end()){
                    new_node->neighbors.push_back(node_map[item]);
                }else{
                    node_queue.push_back(item);
                    UndirectedGraphNode * new_item = new UndirectedGraphNode(item->label);
                    node_map[item] = new_item; 
                    new_node->neighbors.push_back(new_item);
                    visited[item] = true;
                }
            }
        }
        
        return root;
    }
};