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;
    }
}