[LintCode] Clone Graph

Clone Graph

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
/ \
\_/

SOLUTION:

思路上讲这个题可以分两个部分1，遍历图 2，clone图。

遍历需要用到BFS，基本图的搜索都是BFS，那么也就是要用到queue，先讲node进入队列，然后pop的时候访问他的所有neighbors，把没访问过的neighbor放入队列中，依次pop重复以上操作，在这个过程中将入栈的neighbor存入hashmap中，以便以后确认入栈时是否曾经入队列过，保证只放没遍历过的点入队列。在这个题里，用一个指针＋ArrayList模拟一个队列也是没问题的。

clone时，就是要做deep copy。用newnode作为一个map里指向copynode的指针，再次遍历容器里的node，把原来点的neighbors在map里的映射（BFS时候会克隆到）加入新newnode的neighbors里面。

最后return map里的node的映射就可以了

public class Solution {
/**
* @param node: A undirected graph node
* @return: A undirected graph node
*/
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if (node == null){
return null;
}
//because I need the collection 2 times, so I can't use queue, then I choice ArrayList and a pointer(start)
ArrayList<UndirectedGraphNode> nodes = new ArrayList<UndirectedGraphNode>();
HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
nodes.add(node);
map.put(node, new UndirectedGraphNode(node.label));
int start = 0;
//clone nodes
while (start < nodes.size()){
UndirectedGraphNode cur = nodes.get(start++);
for (int i = 0; i < cur.neighbors.size(); i++){
UndirectedGraphNode neighbor = cur.neighbors.get(i);
if (!map.containsKey(neighbor)){
map.put(neighbor, new UndirectedGraphNode(neighbor.label));
nodes.add(neighbor);
}
}
}
// clone neighbors
for (int i = 0; i < nodes.size(); i++){
UndirectedGraphNode newNode = map.get(nodes.get(i));
for (int j = 0; j < nodes.get(i).neighbors.size(); j++){
newNode.neighbors.add(map.get(nodes.get(i).neighbors.get(j)));
}
}
return map.get(node);
}
}

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