clone-graph

class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(node==NULL)return NULL;
        unordered_map<UndirectedGraphNode*,UndirectedGraphNode*>copied;
        clone(node,copied);
        return copied[node];
    }
    UndirectedGraphNode*clone(UndirectedGraphNode*node,unordered_map<UndirectedGraphNode*,
                              UndirectedGraphNode*>&copied)
    {
        if(copied.find(node)!=copied.end())return copied[node];
        UndirectedGraphNode*new_node=new UndirectedGraphNode(node->label);
        copied[node]=new_node;
        for(auto it:node->neighbors)
            new_node->neighbors.push_back(clone(it,copied));
        return new_node;
    }
};