LeetCode #133 - 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. Test the implementation with the following example: Input: 1 -- 2 -- 3, Output: A deep copy of the graph.

``` def cloneGraph(node: 'Node') -> 'Node': if not node: return None clone = {node: Node(node.val)} queue = deque([node]) while queue: curr = queue.popleft() for neighbor in curr.neighbors: if neighbor not in clone: clone[neighbor] = Node(neighbor.val) queue.append(neighbor) clone[curr].neighbors.append(clone[neighbor]) return clone[node] ```