LeetCode 133: Clone Graph

/**
* 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 result = new UndirectedGraphNode(node.label);
Queue<UndirectedGraphNode> queue = new LinkedList<>();
Map<UndirectedGraphNode, UndirectedGraphNode> connections = new HashMap<>();
connections.put(node, result);
queue.offer(node);

while (!queue.isEmpty()) {
UndirectedGraphNode current = queue.poll();

for (UndirectedGraphNode neighbor : current.neighbors) {
if (!connections.containsKey(neighbor)) {
UndirectedGraphNode newNode = new UndirectedGraphNode(neighbor.label);
connections.put(neighbor, newNode);
queue.offer(neighbor);
}
connections.get(current).neighbors.add(connections.get(neighbor));
}
}
return result;
}
}