Clone Graph
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https://oj.leetcode.com/problems/clone-graph/
Clone an undirected graph. Each node in the graph contains a label
and 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#
.
- 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 / \ \_/
/** * Definition for undirected graph. * class UndirectedGraphNode { * int label; * List<UndirectedGraphNode> neighbors; * UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); } * }; */
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node)
这一题虽然说是图的克隆,但其实本质上就是无向图的全遍历。那么DFS和BFS在这里都是可以用的。就是用HashMap来进行路径记录避免循环路径。下面直接给出两段代码吧
DFS(实际上是一个bottom-up回收路径的过程):
public UndirectedGraphNode DFShelper(UndirectedGraphNode node, HashMap<UndirectedGraphNode, UndirectedGraphNode> visited){ if(visited.containsKey(node)) return visited.get(node); UndirectedGraphNode copy_node = new UndirectedGraphNode(node.label); visited.put(node, copy_node); for(UndirectedGraphNode n : node.neighbors){ copy_node.neighbors.add(DFShelper(n, visited)); } return copy_node; }
BFS:
public UndirectedGraphNode BFShelper(UndirectedGraphNode node){ Queue<UndirectedGraphNode> node_queue = new LinkedList<UndirectedGraphNode>(); HashMap<UndirectedGraphNode, UndirectedGraphNode> visited = new HashMap<UndirectedGraphNode, UndirectedGraphNode>(); UndirectedGraphNode res = new UndirectedGraphNode(node.label); visited.put(node, res); node_queue.add(node); while(!node_queue.isEmpty()){ UndirectedGraphNode cur_node = node_queue.poll(); UndirectedGraphNode copy_node = visited.get(cur_node); for(UndirectedGraphNode n : cur_node.neighbors){ UndirectedGraphNode copy_n = visited.containsKey(n) ? visited.get(n) : new UndirectedGraphNode(n.label); copy_node.neighbors.add(copy_n); if(!visited.containsKey(n))node_queue.add(n); visited.put(n, copy_n); } } return res; }
具体说一下哈希表的内容,键是原图的内容,值是拷贝的内容。所以每次DFS递归或者BFS循环的时候,总能在对应的点上取到对应的neighbors copy。BFS比较好理解,DFS实际上就是一个首先top-down遍历路径然后再bottom-up回收路径的一个做法。这在DFS上应该也是很常见的。
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