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/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> neighbors;
    Node() {
        val = 0;
        neighbors = vector<Node*>();
    }
    Node(int _val) {
        val = _val;
        neighbors = vector<Node*>();
    }
    Node(int _val, vector<Node*> _neighbors) {
        val = _val;
        neighbors = _neighbors;
    }
};
*/

class Solution {
public:
    Node* dfs(Node* node,unordered_map<Node*,Node*>&ot){
        Node* clone =new Node(node->val);
        vector<Node*> cneighbor;
        ot[node]=clone;
        for(Node* nbr:node->neighbors){
            if(ot.find(nbr)!=ot.end()){ //clone exists
               cneighbor.push_back(ot[nbr]);
            }else{
                cneighbor.push_back(dfs(nbr,ot)); //calls recursion on the not yet visited neighboring node
            }
        }
        clone->neighbors=cneighbor;
        return clone;
    }

    Node* cloneGraph(Node* node) {
        unordered_map<Node*,Node*> ot;
        if(node==NULL) return NULL;
        if(node->neighbors.size()==0){
            Node* clone=new Node(node->val);
            return clone;
        }
        return dfs(node,ot);
    }
};