LeetCode 133. Clone Graph（克隆图）

原题网址：https://leetcode.com/problems/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
         / \
         \_/

方法：使用哈希映射保存已克隆的节点。

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList(); }
 * };
 */
public class Solution {
    private Map map = new HashMap<>();
    
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) return null;
        UndirectedGraphNode cloned = map.get(node.label);
        if (cloned != null) return cloned;
        cloned = new UndirectedGraphNode(node.label);
        map.put(cloned.label, cloned);
        for(UndirectedGraphNode neighbor: node.neighbors) {
            cloned.neighbors.add(cloneGraph(neighbor));
        }
        return cloned;
    }
}