/**
   This class implements queues of pairs of integers
   as linked lists from the class {@link PairIntList PairIntList}. 
   Insertions are made at the rear and deletions at the front. The link
   is from front to rear (i.e. the front is the head of the linked list.
   The queue is represented by two pointers on {@link PairIntList PairIntList}
   objects <code>front</code> and <code>rear</code>. An empty queue
   is a pair <code>(front, rear)</code> such that <code>front</code>
   is null.

*/
public class PairIntQueue {
    PairIntList front = null, rear = null;
    /**
       Returns true if the pair <code>(val, elem)</code> is in the queue.
    */
    public boolean isIn(int val, int elem){
	for(PairIntList l = front; l != null; l = l.next){
	    if(l.val == val && l.elem == elem)
		return true;
	}
	return false;
    }
    /**
       Adds the pair <code>(val, elem)</code> to the queue.
    */
    public void add(int val, int elem) {
	if(!isIn(val, elem))
	    add(new PairIntList(val, elem, null));
    }
    public void addFast(int val, int elem) {
	    add(new PairIntList(val, elem, null));
    }
    /**
       Adds the head of the list <code>l</code> to the queue.
    */
    public void add(PairIntList l) {
	l.next = null;
	if (front == null)
	    front = rear = l;
	else
	    rear = rear.next = l;
    }
    /**
       Removes the first element of the queue.
       @return the resulting queue (<code>null</code> if the queue
       is empty).
    */
    public PairIntList remove() {
	if (front == null) return null;
	PairIntList result = front;
	if (front == rear)
	    front = rear = null;
	else
	    front = front.next;
	return result;
    }
    /**
       Returns the first element of the queue and removes it.
    */
    public PairInt removeHead() {
	if (front == null) return null;
	PairIntList result = front;
	if (front == rear)
	    front = rear = null;
	else
	    front = front.next;
	return new PairInt(result);
    }
    /**
       Returns <code>true</code> if the queue is empty, which means
       that <code>front</code> is <code>null</code>
    */
    public boolean isEmpty() { return front == null; }
    public String showAI(String name, Alphabet a) {
	return name + " " + PairIntList.showAI(front, a);
    }
    public String showAI(Alphabet a) { return showAI("", a); }
    public String show(String name, Alphabet a) {
	return name + " " + front.show(a);
    }
    public String show(Alphabet a) { return show("", a); }
    
    public static void main(String[] args){
	Alphabet a = new Alphabet(2);
	PairIntQueue q = new PairIntQueue();
	q.add(a.toShort('a'),7);
	System.out.println(q.showAI(a));
    }

} // PairIntQueue.java