Clone Graph

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 value (`int`) and a list (`List[Node]`) of its neighbors. class Node { public int val; public List<Node> neighbors; } ```   **Test case format:** For simplicity, 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. An 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. ```   **Constraints:** - The number of nodes in the graph is in the range `[0, 100]`. - `1 <= Node.val <= 100` - `Node.val` is unique for each node. - There are 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.