LeetCode clone-graph

题目描述

Clone an undirected graph. Each node in the graph contains alabeland a list of itsneighbors.

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 as0. Connect node0to both nodes1and2.
2. Second node is labeled as1. Connect node1to node2.
3. Third node is labeled as2. Connect node2to node2(itself), thus forming a self-cycle.

Visually, the graph looks like the following:

       1
      / \
     /   \
    0 --- 2
         / \
         \_/

解题思路：递归实现

• 建立一个HashSet保存已经copy的节点
• 对于copy节点的neighbors同样进行copy实现

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     ArrayList<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
import java.util.*;
public class Solution {
    HashMap<Integer, UndirectedGraphNode> maps = new HashMap<>();
	public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
		return cloneNode(node);
	}
	
	public UndirectedGraphNode cloneNode(UndirectedGraphNode node) {
		if (node == null)
			return null;
		if (maps.containsKey(node.label)) {
			return maps.get(node.label);
		} 
		UndirectedGraphNode copy = new UndirectedGraphNode(node.label);
        maps.put(node.label, copy);
		for (int i = 0; i < node.neighbors.size(); i++) {
			UndirectedGraphNode nb = cloneGraph(node.neighbors.get(i));
			copy.neighbors.add(nb);
		}
        
		return copy;
	}
}