/**
   This class implements queues of integers as linked lists
   from the class {@link IntList IntList}. Insertions are
   made at the rear and deletions at the front. The link
   is from front to rear.

*/
public class IntQueue {
    IntList front = null, rear = null;
    int size = 0;
    /**
       Adds the integer <code>val</code> to the queue.
       @param val an integer.
    */
    public void add(int val) {
	size++;
	if (front == null)
	    front = rear = new IntList(val, null);
	else
	    rear = rear.next = new IntList(val, null);
    }
    /**
       Adds the list <code>l</code> at the rear of the queue.
       @param l a linked list of integers.
    */
    public void add(IntList l) {
	size++;
	l.next = null;
	if (front == null)
	    front = rear = l;
	else
	    rear = rear.next = l;
    }
    /**
       Removes the first element of the queue.
       Returns <code>null</code> if the queue is empty.
       @return the resulting queue.
    */
    public IntList remove() {
	if (front == null) return null;
	IntList result = front;
	if (front == rear)
	    front = rear = null;
	else
	    front = front.next;
	size--;
	return result;
    }
    /**
       Empties the queue.
    */
    public void  removeAll() {
	front = rear = null;
	size = 0;
    }
    /**
       Returns true if the queue is empty.
    */
    public boolean isEmpty() { return front == null; }
    /**
       Returns the size of the queue.
    */
    public int size() { return size; }
    /**
       Returns the last element of the queue.
    */
    public int lastVal() { return rear.val; }
    /**
       Returns the penultimate value.
    */
    public int removeVal() { return remove().val; }
    /**
       Adds all the elements of the queue <code>s</code>
       and empties <code>s</code>.
    */
    public void seizeAll(IntQueue s) {
	if (front == null) 
	    front = s.front; 
	else
	    rear.next = s.front;
	rear = s.rear;
	size += s.size;
	s.removeAll();
    }
    public String toString() {
	return front.toString();
    }
    public String show(String name) {
	return name + " "+ front;
    }
    /**
       Concatenates the current queue and the queue <code>s</code>.
       @return the resulting queue.
    */
    public IntQueue append(IntQueue x) {
	if (x.isEmpty())
	    return this;
	if (this.isEmpty()) {
	    front = x.front; rear = x.rear; size = x.size;
	}
	else {
	    rear.next = x.front;
	    rear = x.rear;
	    size += x.size;
	}
	return this;
    } 
    /**
       A variant of <code>append()</code>.
    */ 
    public IntQueue concat(IntQueue x) {
	while (!x.isEmpty())
	    add(x.removeVal());
	return this;
    }  
		       
} // IntQueue