Clone_Graph

题目描述：

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

         / \

         \_/

思路：BFS，需要注意的一点是对死循环的处理，例如1——2,两个节点，遍历1时，2为1的邻节点，当遍历到2时，1又为2的邻节点所以就会产生一个遍历循环，所以当遍历到遍历过的点便不再将其放入遍历队列，还有就是当一个节点的相邻子节点没有被复制，要先将其复制并放入遍历队列。

public class Clone_Graph {
public static UndirectedGraphNode cloneGraph(UndirectedGraphNode node)
{
if(node==null)
return node;
UndirectedGraphNode newGraph = new UndirectedGraphNode(node.label);
//存放要遍历的节点
ArrayList<UndirectedGraphNode> queue = new ArrayList<UndirectedGraphNode>();
//存放已经复制了的节点
HashMap<UndirectedGraphNode,UndirectedGraphNode> visited = new HashMap<UndirectedGraphNode,UndirectedGraphNode>();
queue.add(newGraph);
visited.put(node,newGraph);

while(queue.size()>0)
{
UndirectedGraphNode original = queue.get(0);
ArrayList<UndirectedGraphNode> list = original.neighbors;
queue.remove(0);
for(int i=0;i<list.size();i++)
{
if(visited.containsKey(list.get(i)))
{
visited.get(original).neighbors.add(list.get(i));
}
else
{
UndirectedGraphNode newNode = new UndirectedGraphNode(list.get(i).label);
visited.get(original).neighbors.add(newNode);
visited.put(list.get(i),newNode);
queue.add(newNode);
}
}
}
return newGraph;
}
public static void main(String[] args) {
UndirectedGraphNode node = new UndirectedGraphNode(0);
cloneGraph(node);
}
}