Clone an undirected graph. Each node in the graph contains a `label`

and a list of its `neighbors`

.

How we serialize an undirected graph:

Nodes are labeled uniquely.

We use `#`

as a separator for each node, and `,`

as a separator for node label and each neighbor of the node.

As an example, consider the serialized graph `{0,1,2#1,2#2,2}`

.

The graph has a total of three nodes, and therefore contains three parts as separated by `#`

.

- First node is labeled as
`0`

. Connect node `0`

to both nodes `1`

and `2`

.
- Second node is labeled as
`1`

. Connect node `1`

to node `2`

.
- Third node is labeled as
`2`

. Connect node `2`

to node `2`

(itself), thus forming a self-cycle.

Visually, the graph looks like the following:

```
1
/ \
/ \
0 --- 2
/ \
\_/
```