leetcode-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
/ \
\_/

拷贝一个无向图。可以用递归来拷贝，在拷贝一个节点后，对它的邻节点递归地调用拷贝操作，要注意判断邻节点
是否已经被拷贝过。

class Solution {
public:
UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
mLabelNodes.clear();
return clone(node);
}

private:
map<int, UndirectedGraphNode*> mLabelNodes;     // The node* set have been cloned

UndirectedGraphNode *clone(UndirectedGraphNode *node) {
UndirectedGraphNode *ret = NULL;

if (node == NULL)
return ret;

ret = new UndirectedGraphNode(node->label);
mLabelNodes.insert(make_pair(ret->label, ret));

map<int, UndirectedGraphNode*>::iterator it;

for (int i=0; i<node->neighbors.size(); ++i) {
it = mLabelNodes.find(node->neighbors[i]->label);

if (it != mLabelNodes.end())
ret->neighbors.push_back((*it).second);
else
ret->neighbors.push_back(clone(node->neighbors[i]));
}

return ret;
}
};