LeetCode 133. Clone Graph（克隆圖）

原題網址：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  . Connect node   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：使用哈希映射儲存已克隆的節點。

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    private Map<Integer, UndirectedGraphNode> 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;
    }
}