[leedcode 133] Clone Graph

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

label

and a list of its

neighbors

.

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 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
/ \
\_/

/**
* Definition for undirected graph.
* class UndirectedGraphNode {
*     int label;
*     List<UndirectedGraphNode> neighbors;
*     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
* };
*/
public class Solution {
使用深度优先搜索。这样可以递归实现，如果是宽度优先，就要额外使用queue容器。
关键点：
1 这里的clone需要深度拷贝，就是要使用new操作了
2 防止回路无限循环，就要使用hash表，这里使用map记录访问过的节点。因为这里的label应该是唯一的才对，所以可以直接使用label作为关键字就可以。
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if(node==null) return null;
HashMap<Integer,UndirectedGraphNode> map=new HashMap<Integer,UndirectedGraphNode>();
return clone(node,map);
}
public UndirectedGraphNode clone(UndirectedGraphNode node,HashMap<Integer,UndirectedGraphNode> map){
if(map.containsKey(node.label)) return map.get(node.label);
UndirectedGraphNode newNode=new UndirectedGraphNode(node.label);
map.put(node.label,newNode);////注意标记的位置
for(UndirectedGraphNode n:node.neighbors){
newNode.neighbors.add(clone(n,map));/////
}
return newNode;
}
}