133. Clone Graph
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题目:
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 / \_/
链接: http://leetcode.com/problems/clone-graph/
5/14/2017
14ms, 9%
用BFS的方法,先建立每个元素的copy,然后如果neighbor没有建立copy,把neighbor也放在queue当中。第二部分就是链接各个节点。
还要注意iterate through hashmap
1 /** 2 * Definition for undirected graph. 3 * class UndirectedGraphNode { 4 * int label; 5 * List<UndirectedGraphNode> neighbors; 6 * UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); } 7 * }; 8 */ 9 public class Solution { 10 public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) { 11 if (node == null) return null; 12 13 Map<UndirectedGraphNode, UndirectedGraphNode> graphMap = new HashMap<UndirectedGraphNode, UndirectedGraphNode>(); 14 Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>(); 15 16 queue.offer(node); 17 // create copy of new nodes 18 while (!queue.isEmpty()) { 19 UndirectedGraphNode n = queue.poll(); 20 if (!graphMap.containsKey(n)) { 21 UndirectedGraphNode copy = new UndirectedGraphNode(n.label); 22 graphMap.put(n, copy); 23 } 24 for (UndirectedGraphNode neighbor: n.neighbors) { 25 if (!graphMap.containsKey(neighbor)) { 26 queue.offer(neighbor); 27 } 28 } 29 } 30 // build neighbors 31 for (Map.Entry<UndirectedGraphNode, UndirectedGraphNode> entry: graphMap.entrySet()) { 32 UndirectedGraphNode original = entry.getKey(); 33 UndirectedGraphNode copy = entry.getValue(); 34 for (UndirectedGraphNode neighbor: original.neighbors) { 35 copy.neighbors.add(graphMap.get(neighbor)); 36 } 37 } 38 return graphMap.get(node); 39 } 40 }
也可以在copy的时候直接建立neighbors
https://discuss.leetcode.com/topic/4690/simple-java-iterative-bfs-solution-with-hashmap-and-queue
DFS做法
https://discuss.leetcode.com/topic/9629/depth-first-simple-java-solution
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