public class Queue {
  private Node head = null, tail = null;

  private class Node {
    public String data;
    public Node   next;
    public Node(String d, Node n) {
      data = d;
      next = n;
    }
  }

  public void enqueue(String s) {
    if( head == null ) {
      head = tail = new Node(s, null);
    } else {
      tail.next = new Node(s, null);
      tail      = tail.next;
    }
  }

  public String dequeue() {
    Node t = head;

    head = head.next;
    if( head == null )
      tail = null;

    return t.data;
  }

  public boolean empty() {
    return head == null;
  }

  public String[] toArray() {
    // Assumes at least one node exists.
    // (a dumb way to do it, but don't change this).
    Node t = head;
    int n = 1;
    while( t.next != null ) {
      t = t.next;
      n++;
    }
      
    // Create array and return it.
    String[] arr = new String[n];
    int i = 0;
    for( t = head; t != null; t = t.next )
      arr[i++] = t.data;
    return arr;
  }
}