【LeetCode】Clone Graph 解題報告
阿新 • • 發佈:2019-01-10
【題目】
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 node0
to both nodes1
and2
. - Second node is labeled as
1
. Connect node1
to node2
. - Third node is labeled as
2
. Connect node2
to node2
(itself), thus forming a self-cycle.
Visually, the graph looks like the following:
1 / \ / \ 0 --- 2 / \ \_/
【思路】
這道題主要是資料結構的應用吧,用一個佇列存放圖中還未被訪問的結點,用一個map存放克隆的新結點。對於佇列中的結點,訪問其鄰居,如果該鄰居已經被克隆,那麼只需維護克隆結點之間的鄰居關係即可,如果該鄰居尚未被克隆,那麼需要new一個新的結點作為它的克隆,並維護克隆後的鄰居關係。
【Java程式碼】
/** * 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; UndirectedGraphNode clone = new UndirectedGraphNode(node.label); //用一個Map來儲存已經克隆的新結點 HashMap<Integer, UndirectedGraphNode> map = new HashMap<Integer, UndirectedGraphNode>(); map.put(node.label, clone); //用一個佇列來儲存沒有訪問過的結點 LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>(); queue.add(node); while (!queue.isEmpty()) { UndirectedGraphNode originalnode = queue.remove(); UndirectedGraphNode clonenode = map.get(originalnode.label); for (int i = 0; i < originalnode.neighbors.size(); i++) { UndirectedGraphNode neighbor = originalnode.neighbors.get(i); //如果該鄰居結點已被克隆 if (map.get(neighbor.label) != null) { clonenode.neighbors.add(map.get(neighbor.label)); continue; } //把該鄰居放入queue中 queue.add(neighbor); //克隆該鄰居結點 UndirectedGraphNode newnode = new UndirectedGraphNode(neighbor.label); //把新結點放入map中 map.put(neighbor.label, newnode); //把新結點加入鄰居集中 clonenode.neighbors.add(newnode); } } return clone; } }