Clone Graph

Given a reference of a node in a connected undirected graph. Return a clone of the graph.
Each node in the graph contains a value (Integer) and a list (List[Node]) of its neighbors.

• Time : O(v + e)
• Space : O(v)

class Solution {
    unordered_map<Node*, Node*> mp;
    Node* helper(Node* node) {
        if(mp.count(node)) return mp[node];
        mp[node] = new Node(node->val);
        for(auto& n : node->neighbors) {
            mp[node]->neighbors.push_back(helper(n));
        }
        return mp[node];
    }
public:
    Node* cloneGraph(Node* node) {
        mp.clear();
        return helper(node);
    }
};