## Clone Graph

### 描述

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbours.

OJ's undirected graph serialization: Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbour 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 #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. 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
/ \
\_/


### DFS

// Clone Graph
// DFS，时间复杂度O(n)，空间复杂度O(n)
public class Solution {
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if(node == null) return null;
// key is original node，value is copied node
HashMap<UndirectedGraphNode, UndirectedGraphNode> visited = new HashMap<>();
clone(node, visited);
return visited.get(node);
}
// DFS
private static UndirectedGraphNode clone(UndirectedGraphNode node,
HashMap<UndirectedGraphNode,
UndirectedGraphNode> visited) {
if (visited.containsKey(node)) return visited.get(node);

UndirectedGraphNode new_node = new UndirectedGraphNode(node.label);
visited.put(node, new_node);
for (UndirectedGraphNode nbr : node.neighbors)
return new_node;
}
}


### BFS

// Clone Graph
// BFS，时间复杂度O(n)，空间复杂度O(n)
public class Solution {
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if (node == null) return null;
// key is original node，value is copied node
HashMap<UndirectedGraphNode,UndirectedGraphNode> visited = new HashMap<>();
// each node in queue is already copied itself
// but neighbors are not copied yet
q.offer(node);
visited.put(node, new UndirectedGraphNode(node.label));
while (!q.isEmpty()) {
UndirectedGraphNode cur = q.poll();
for (UndirectedGraphNode nbr : cur.neighbors) {
if (visited.containsKey(nbr)) {
} else {
UndirectedGraphNode new_node =
new UndirectedGraphNode(nbr.label);
visited.put(nbr, new_node);