/**
 * Definition for graph node.
 * class GraphNode {
 *     int label;
 *     ArrayList<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) {
 *         label = x; neighbors = new ArrayList<UndirectedGraphNode>();
 *     }
 * };
 */
public class Solution {
    /**
     * @param graph a list of Undirected graph node
     * @param values a hash mapping, <UndirectedGraphNode, (int)value>
     * @param node an Undirected graph node
     * @param target an integer
     * @return the a node
     */
    public UndirectedGraphNode searchNode(ArrayList<UndirectedGraphNode> graph,
                                          Map<UndirectedGraphNode, Integer> values,
                                          UndirectedGraphNode node,
                                          int target) {
        // Write your code here
        Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        Set<UndirectedGraphNode> hash = new HashSet<UndirectedGraphNode>();

        queue.offer(node);
        hash.add(node);

        while (!queue.isEmpty()) {
            UndirectedGraphNode head = queue.poll();
            if (values.get(head) == target) {
                return head;
            }
            for (UndirectedGraphNode nei : head.neighbors) {
                if (!hash.contains(nei)){
                    queue.offer(nei);
                    hash.add(nei);
                }
            }
        }
        return null;
    }
}