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
         / 
         \_/

直接用HashMap来做应该是最简单的，这个对十字链表也可以。使用hashmap来存储node的对应关系。

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     ArrayList<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        map.clear();
        return cloneNode(node);
    }
     
    private UndirectedGraphNode cloneNode(UndirectedGraphNode node)
    {
        if (node == null) return null;
        if (map.containsKey(node)) return map.get(node);
        else
        {
            UndirectedGraphNode copy = new UndirectedGraphNode(node.label);
            map.put(node, copy);
            for (UndirectedGraphNode n : node.neighbors)
            {
                copy.neighbors.add(cloneNode(n));
            }
            return copy;
        }
    }
}