CompSci 105 SS 2005 Principles of Computer Science

CompSci 105 SS 2005 Principles of Computer Science Lecture 11: Linked Lists

The Wall ADT Operations Program that uses the ADT ADT Implementation

public class AreaCircle implements Circle { private float x, y, radius, area; public void setRadius( float newR ) { radius = newRadius; area = Math.PI * radius * radius ); } public void getArea() { return ( area ); } }

public class AreaCircle implements Circle { private float x, y, radius; public void setRadius( float newR ) { radius = newRadius; } public void getArea() { return (Math.PI * radius * radius ); } }

public class AreaCircle implements Circle { public void setRadius( float newR ) { } public void getArea() { return (Math.PI * Math.random()*50 ); } }

Lists What is a list?

List ADT • createList() • isEmpty() • size() • add( index, item) • remove(index) • removeAll() • get(index) • Milk • Eggs • Butter • Apples • Bread • Chicken

A few list ADT operations • list.get(3)

A few list ADT operations • list.get(3) • list.remove(3)

A few list ADT operations • list.get(3) • list.remove(3) • list.add(3, butter)

A few list ADT operations • list.get(3) • list.remove(3) • list.add(3, butter) • list.add(3, beer)

Resizable Arrays 0 1 2 3 1 3 7 8 myArray:

Resizable Arrays 0 1 2 3 1 3 7 8 myArray: tempArray: 0 1 2 3 4 5 6 7

Resizable Arrays 0 1 2 3 1 3 7 8 myArray: 0 1 2 3 4 5 6 7 1 3 7 8 tempArray:

Advantages/Disadvantagesof Using Arrays??How could we do this “better”?

Linked Lists The Node class Lists as Recursive Structures Displaying a Linked List Inserting and Deleting Elements Implementing the ADT List

List ADT • createList() • isEmpty() • size() • add( index, item) • remove(index) • removeAll() • get(index)

A few list ADT operations • list.get(int itemNum) • list.get(3); • list.remove(int itemNum) • list.remove(3); • list.add(int itemNum, Object data) • list.add(3, “beer”);

We know already that an ArrayList works this way. • What other ways could we satisfy this Abstract implementation?

A Node Data Structure public class Node { private Object item; private Node next; } Beer Wine

Recursive Definition • Milk • Eggs • Butter • Apples • Bread • Chicken A List is the first item, followed by a List

Terminology Head Node Node Node Beer Milk Wine

ListReferenceBased Class public class ListReferenceBased { private Node head; private int numItems; } Beer Milk Wine 3

Node class public class Node { private Object item; private Node next; public Object getItem() {return item;} public Node getNext() {return next;} public void setItem(Object i) {item=i;} public void setNext(Node n) {next=n;} } Beer

public void printList( ) { Node curr = head; while (curr != null ) { System.out.println( curr.getItem() ); curr = curr.getNext(); } } Beer Milk Wine head

How would we insert and delete an element from an ArrayList??

Deleting the First Node Beer Milk Wine head

Deleting the First Node public void deleteFirstNode() if ( head == null ) // Handle error condition else head = head.getNext(); } Beer Milk Wine head

Inserting at Front Milk Wine head

Inserting at Front public void insertAtFront( Object item ) Node temp = head; head = new Node(); head.setItem( item ); head.setNext( temp ); } Milk Wine head

public void remove(int index) Node prev = null; Node curr = head; while ( index > 1 ) { prev = curr; curr = curr.getNext(); index = index-1; } prev.setNext( curr.getNext() ); } prev curr Beer Milk Wine head

What does this list look like? • Node n5 = new Node(15); • Node n6 = new Node(34); • Node n7 = new Node(12); • Node n8 = new Node(84); • n6.next = n5; • n7.next = n8; • n8.next = n6; • n5.next = null;

Other Types of List • Doubly Linked Lists • Circular Linked Lists • ...more to come later

Doubly Linked Lists Beer Milk Wine head

Circular Linked Lists Beer Milk Wine head

How would we add/remove in this scenario?

CompSci 105 SS 2005 Principles of Computer Science