[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 from 0 to N - 1, where N is the total nodes in the graph.

We use # as a separator for each node, and , as a separator for each neighbor of the node.

As an example, consider the serialized graph {1,2#2#2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

1. Connect node 0 to both nodes 1 and 2.
2. Connect node 1 to node 2.
3. 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 *clone(UndirectedGraphNode *node, map<int,UndirectedGraphNode*> &table)
    {
        if(node==NULL)
            return NULL;
            
        if(table.find(node->label)!=table.end())
            return table[node->label];
        
        UndirectedGraphNode *newnode=new UndirectedGraphNode(node->label);
        table[newnode->label]=newnode;

        for(int i=0;i<node->neighbors.size();i++)
        {
            UndirectedGraphNode *neighbor=clone(node->neighbors[i],table);
            newnode->neighbors.push_back(neighbor);
        }
        
        return newnode;
    }

    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        //keep a hash table to check whether this node is visited or not
        map<int,UndirectedGraphNode*> visitTable;
        return clone(node,visitTable);
    }
};