solution.cpp

#include <bits/stdc++.h>
using namespace std;

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 *cloneGraph(Node *node)
    {
        unordered_map<Node *, Node *> m;
        return helper(node, m);
    }
    Node *helper(Node *node, unordered_map<Node *, Node *> &m)
    {
        if (!node)
            return NULL;
        if (m.count(node))
            return m[node];
        Node *clone = new Node(node->val);
        m[node] = clone;
        for (Node *neighbor : node->neighbors)
        {
            clone->neighbors.push_back(helper(neighbor, m));
        }
        return clone;
    }
};