Leetcode 133: Clone Graph

https://leetcode.com/problems/clone-graph/description/

Given a reference of a node in a connected undirected graph, return a deep copy (clone) of the graph. Each node in the graph contains a val (int) and a list (List[Node]) of its neighbors.

Example:

Input:
{"$id":"1","neighbors":[{"$id":"2","neighbors":[{"$ref":"1"},{"$id":"3","neighbors":[{"$ref":"2"},{"$id":"4","neighbors":[{"$ref":"3"},{"$ref":"1"}],"val":4}],"val":3}],"val":2},{"$ref":"4"}],"val":1}

Explanation:
Node 1's value is 1, and it has two neighbors: Node 2 and 4.
Node 2's value is 2, and it has two neighbors: Node 1 and 3.
Node 3's value is 3, and it has two neighbors: Node 2 and 4.
Node 4's value is 4, and it has two neighbors: Node 1 and 3.

Note:

1. The number of nodes will be between 1 and 100.
2. The undirected graph is a simple graph, which means no repeated edges and no self-loops in the graph.
3. Since the graph is undirected, if node p has node q as neighbor, then node q must have node p as neighbor too.
4. You must return the copy of the given node as a reference to the cloned graph.

Notes:

The key is to avoid multiple copies of the same node. So we can used a hash map to build up a one-to-one relationship.

Either BFS or the DFS will work.

See the code below:

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

class Solution {
public:
    Node* cloneGraph(Node* node) {
        if(!node) return node;
        Node* copy = new Node(node->val, {});
        unordered_map<Node*, Node*> mp;
        mp[node] = copy;
        queue<Node*> q;
        q.push(node);
        while(q.size()) {
            auto t = q.front();
            q.pop();
            for(auto &a : t->neighbors) {
                if(!mp.count(a)) {
                    mp[a] = new Node(a->val, {});
                    q.push(a);
                }
                mp[t]->neighbors.push_back(mp[a]);
            }
        }
        return copy;
    }
};