Linked Lists

1. Linked Lists CSC 172 SPRING 2004 LECTURE 6

2. ANNOUNCEMENTS • Project 2 due Wed, Feb 18th, 5PM, CSB • Read Weiss Chapter 17 • Department T shirts available $10 • Get some paper out

3. Self-referential data types class Node { private Object data; // the “data” private Node next; // the “link” }

4. Linked List • A linked list “has-a” reference to a node • The “head” of the list • The ending node has “null” for the next head

5. Basic Linked List

6. Exercise 1 Implement a method public static void printList(Node front){} That traverses and prints the list

7. public static void printList(Node front) { while (front != null) { System.out.println(front.toString()); front = front.next; } }

8. public static void printList(Node front) { if (front == null) return; else { System.out.println(front.toString()); printList(front.next); } }

9. Exercise 2 Implement a method public static void printList(Node front){} That traverses and prints the list in reverse

10. public static void printList(Node front) { if (front == null) return; else { printList(front.next); System.out.println(front.toString()); } }

11. Exercise 3 Implement a method public static Object lookup(Node front, Comparable searchobj){ // return null if not found }

12. Adding a first node public void addFirst(Obj obj)

13. Adding a first node public void addFirst(Object obj){ Link newLink = new Link(); newLink.data = obj; newLink.next = first; first = newLink; }

14. Deleting a first node public Object removeFirst() {}

15. Deleting a first node public Object removeFirst(){ if (first == null) throw new NoSuchElementException(); Object obj = first.data; first = first.next; return obj; }

16. Doubly Linked List Ex 4 : Write the “DoubleNode” class

17. An empty Doubly Linked List How does this (the existence of head & tail) change traverse & print?

18. Deletion Ex 6: Write a method to delete from doubly linked list assume comparable Objects public void delete(Comparable obj)

19. public void delete (Comparable obj) { Node current = head; while (current != tail) { if (obj.equals(current.data)) { (current.next).prev = current.prev; (current.prev).next = current.next; return; } current = current.next; } }

20. Insertion Ex 6: Write a method to insert from doubly linked list public void insertAfter(Node n, Comparable obj)

21. public void insertAfter(Node n, Object obj){ Node newNode = new DoubleNode(); newNode.data = obj; newNode.prev = n; newNode.next = n.next; (newNode.prev).next = newNode; (newNode.next).prev = newNode; }

22. A List Iterator

23. Iterator Functionality

24. Iterator next public Object next() { if (position == null){ position = first; return getFirst(); } else { if (position.next == null) throw new NoSuchElementException(); previous = position; // remember for remove position = position.next; return position.data; } }

25. Adding to middle

26. Adding to middle public void add(Object obj){ if (position == null) addFirst(obj); else { Link newLink = new Link(); newLink.data = obj; newLink.next = position.next; position.next = newLink; position = newLink; previous = null; } }

27. Removing from middle

28. Removing from middle public void remove(){ if (position == first) removeFirst(); else{ if (previous == null) throw new IllegalStateException(); previous.next = position.next; position = previous; } previous = null; } }