/*

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

/ \

\_/

*/

/**

* Definition for undirected graph.

* class UndirectedGraphNode {

* int label;

* ArrayList<UndirectedGraphNode> neighbors;

* UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }

* };

*/

// Basic idea is to use memoization to reduce duplicate computation and avoid cycles

// Maintain a map<oldNode, newNode>, if the oldNode is in the map, get newNode from the map directly;

// otherwise, create a new node

// DFS

public class Solution {

public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {

return clone(node, new HashMap<UndirectedGraphNode, UndirectedGraphNode>());

}

public UndirectedGraphNode clone(UndirectedGraphNode node, HashMap<UndirectedGraphNode, UndirectedGraphNode> map){

if (node == null) return null;

if (map.containsKey(node)) return map.get(node);

UndirectedGraphNode res = new UndirectedGraphNode(node.label);

map.put(node, res);

if (node.neighbors == null || node.neighbors.size() == 0) return res;

for (UndirectedGraphNode n : node.neighbors)

res.neighbors.add(clone(n, map));

return res;

}

}

// BFS

public class Solution {

public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {

if (node==null) return null;

Queue<UndirectedGraphNode> qu = new LinkedList<UndirectedGraphNode>();

Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();

qu.add(node);

while (!qu.isEmpty()){

UndirectedGraphNode curr = qu.poll();

if (!map.containsKey(curr))

map.put(curr, new UndirectedGraphNode(curr.label));

for (UndirectedGraphNode adj : curr.neighbors){

if (!map.containsKey(adj)){

map.put(adj, new UndirectedGraphNode(adj.label));

qu.add(adj);

}

map.get(curr).neighbors.add(map.get(adj));

}

}

return map.get(node);

}

}