# leetcode\_133

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.

```java
class Node {
    public int val;
    public List<Node> neighbors;
}
```

Test case format:

For simplicity sake, each node's value is the same as the node's index (1-indexed). For example, the first node with val = 1, the second node with val = 2, and so on. The graph is represented in the test case using an adjacency list.

Adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph.

The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph.

Example 1:

Input: adjList = \[\[2,4],\[1,3],\[2,4],\[1,3]] Output: \[\[2,4],\[1,3],\[2,4],\[1,3]] Explanation: There are 4 nodes in the graph. 1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). 3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). Example 2:

Input: adjList = \[\[]] Output: \[\[]] Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors. Example 3:

Input: adjList = \[] Output: \[] Explanation: This an empty graph, it does not have any nodes. Example 4:

Input: adjList = \[\[2],\[1]] Output: \[\[2],\[1]]

Constraints:

1 <= Node.val <= 100 Node.val is unique for each node. Number of Nodes will not exceed 100. There is no repeated edges and no self-loops in the graph. The Graph is connected and all nodes can be visited starting from the given node.

## Solutions

1. **hash map**

```cpp
/*
// 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:
    unordered_map<Node *, Node *> m {{nullptr, nullptr}};
    Node* cloneGraph(Node* node) {
        if (m.count(node))
            return m[node];
        else {
            // not exist, build hash map
            Node * cur = m[node] = new Node(node->val);
            for (auto pn : node->neighbors)
                cur->neighbors.push_back(cloneGraph(pn));
            return cur;
        }
    }
};
```