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 #.

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         / \         \_/

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/** * Definition for undirected graph. * class UndirectedGraphNode { *     int label; *     List<UndirectedGraphNode> neighbors; *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); } * }; */public class Solution {    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {        if(node == null)return null;        HashMap<Integer,UndirectedGraphNode> checker = new HashMap<>();        return clone(node,checker);    }    private UndirectedGraphNode clone(UndirectedGraphNode node,HashMap<Integer,UndirectedGraphNode> checker){        if(checker.containsKey(node.label)){            return checker.get(node.label);        }        UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);        checker.put(node.label,newNode);                // newNode.neighbors = new ArrayList<UndirectedGraphNode>(node.neighbors);        for(UndirectedGraphNode temNode:node.neighbors){            newNode.neighbors.add(clone(temNode, checker));        }        return newNode;    }}