Question

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 #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
Second node is labeled as 1. Connect node 1 to node 2.
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
     / \
     \_/

Thinking:

  • Method 1:DFS
/**
 * 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) {
        Map<Integer, UndirectedGraphNode> map = new HashMap<>();
        return node == null ? null : dfs(node, map);
    }
    private UndirectedGraphNode dfs(UndirectedGraphNode node, Map<Integer, UndirectedGraphNode> map){
        if(map.containsKey(node.label)) return map.get(node.label);
        UndirectedGraphNode temp = new UndirectedGraphNode(node.label);
        map.put(node.label, temp);
        for(UndirectedGraphNode n : node.neighbors){
            temp.neighbors.add(dfs(n, map));
        }
        return temp;
    }
}

二刷

  1. 参考了一刷，使用BFS。 
    /**
 * 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;
     Map<Integer, UndirectedGraphNode> map = new HashMap<>();
     return dfs(node, map);
 }
 private UndirectedGraphNode dfs(UndirectedGraphNode node, Map<Integer, UndirectedGraphNode> map){
     if(map.containsKey(node.label)) return map.get(node.label);
     UndirectedGraphNode res = new UndirectedGraphNode(node.label);
     map.put(node.label, res);
     for(UndirectedGraphNode n : node.neighbors){
         res.neighbors.add(dfs(n, map));
     }
     return res;
 }
}