CSC153, Class 48: Linear Structures

Overview:
* Deletion in linked lists
* Overview of linear structures
* Stacks
* Queues
* Implementation notes

Notes:
* Reminder: CSC151 has cool project presentations
  Monday at 2:15
* Read more of Bailey
* Sorry, exams not graded yet
* Food: Dried fruit, chocolate

Reminder: Linked lists implement lists a lot like Scheme
does, with "Nodes" that contain a value and a successor

----------------------------------------

Lists are comparatively complex collections

We often want simpler collections with only a few operations:
* add something to the collection
* get something from the collection, removing it after
  getting it
* check if the collection is empty
* check if the collection is full

Someone decided that we should define an ADT called the
"Linear Structure" that supports these operations

What policy for get?
* "Random"
* "Easiest for programmer"
* "Most recently added" LIFO, "Stack"
* "Least recently added", FIFO "Queue" 
* "Most important", "Priority Queue"
* "Least important", "Priority Queue"

Other possible methods that don't overly complicate 
the structures?

* peek, like get but no removal
* size

Note:

Once we've defined Linear we can write

public interface Queue
  extends Linear
{
} // interface Queue

Why bother?
* So that people can say "I want a queue" when they want a
  queue and not "I want a linear structure" and hope to get
  a queue.

To a traditional computer scientist, the primary Queue methods
are enqueue and dequeue

"When you write queue ten thousand times, it starts to get freaky."

To a traditional computer scientist, the primary Stack methods
are push and pop.

How can you implement queues, stacks, and other linear structures?
* Use Nodes (without previous)
* Use an array
* Use a list

public class BriansQueue
  implements Queue
{
  // Fields
  Node first;
  Node last;
 
  public Object get()
    throws EmptyStructureExcepction 
  {
    if (this.first == null)
      throw new EmptyStructureException;
    Object tmp = this.first.value;
    this.first = this.first.next;
    return tmp;
  }
  
  public void add(Object value)
  {
    this.last.next = new Node(value);
    this.last = this.last.next;
  } // add(Object)

} // class BriansQueue

FOR MONDAY, FIGURE OUT WHAT'S WRONG WITH EACH

1. Think about empty queues

ENJOY WALTZ.  BEHAVE RESPONSIBLY.