Clone Graph

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:

/**
* Definition for undirected graph.
* class UndirectedGraphNode {
*     int label;
*     ArrayList<UndirectedGraphNode> neighbors;
*     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
* };
*/
public class Solution {
/**
* @param node: A undirected graph node
* @return: A undirected graph node
*/
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if (node == null) {
return null;
}
//使用BFS获取所有的点
ArrayList<UndirectedGraphNode> nodes = bfsHelper(node);
//copy 点
HashMap<UndirectedGraphNode, UndirectedGraphNode> mapping = new HashMap<>();
for (UndirectedGraphNode n : nodes) {
mapping.put(n, new UndirectedGraphNode(n.label));
}
//copy 边
for (UndirectedGraphNode n : nodes) {
//取出原节点对应的新节点
UndirectedGraphNode newNode = mapping.get(n);
for (UndirectedGraphNode neighbor : n.neighbors) {
//取出原节点的邻接点对应的新节点的邻接点
UndirectedGraphNode newNeighbor = mapping.get(neighbor);
//将其赋值给新节点的邻接点
newNode.neighbors.add(newNeighbor);
}
}
return mapping.get(node);
}
//图的BFS使用Set来保证每个节点遍历一次和边无关
private ArrayList<UndirectedGraphNode> bfsHelper(UndirectedGraphNode node) {
ArrayList<UndirectedGraphNode> nodes = new ArrayList<>();
Queue<UndirectedGraphNode> queue = new LinkedList<>();
Set<Integer> hash = new HashSet<>();
queue.offer(node);
hash.add(node.label);
while (!queue.isEmpty()) {
UndirectedGraphNode temp = queue.poll();
nodes.add(temp);
for (UndirectedGraphNode neighbor : temp.neighbors) {
if (hash.contains(neighbor.label)) {
continue;
}
queue.offer(neighbor);
hash.add(neighbor.label);
}
}
return nodes;
}
}