CS 307 Fundamentals of Computer Science 1 Linked Lists many slides taken from Mike Scott, UT Austin

CS 307 Fundamentals of Computer Science 2 Recursive Data Structures  Linked Lists are dynamic data structures –They grow and shrink one element at a time, normally without some of the inefficiencies of arrays  Big O of Array Manipulations –Access the kth element –Add or delete an element in the middle of the array while maintaining relative order –adding element at the end of array? space avail? no space avail? –add element at beginning of an array  If accesses are all at beginning or end of list, a linked structure offers improvements  Linked Lists could be used as the underlying storage container for higher level ADTs (stack, queue)

CS 307 Fundamentals of Computer Science 3 Nodes and Lists  A different way of implementing a list  Each element of a Linked List is a separate Node object.  Each Node tracks a single piece of data plus a reference (pointer) to the next  Create a new Node every time we add something to the List  Remove nodes when item removed from list and allow garbage collector to reclaim that memory

CS 307 Fundamentals of Computer Science 4 Elements of Linked Lists public class Node {private Object myData; private Node myNext; public Node() {myData = null; myNext = null;} public Node(Object data, Node next) {myData = data;myNext = next; } public Object getData() {return myData;} public Node getNext() {return myNext;} public void setData(Object data) {myData = data;} public void setNext(Node next) {myNext = next;} }

CS 307 Fundamentals of Computer Science 5 One Implementation of a Linked List  The Nodes shown on the previous slide are singly linked –a node refers only to the next node in the structure –it is also possible to have doubly linked nodes. –The node has a reference to the next node in the structure and the previous node in the structure as well  How is the end of the list indicated –myNext = null for last node –a separate dummy node class / object

CS 307 Fundamentals of Computer Science 6 A Simple List Interface public interface IList { void add(Object item); void add(Object item, int pos); Object set(Object item, int pos); void add(List other); Object get(int pos); Object remove(int pos); int size(); }

CS 307 Fundamentals of Computer Science 7 A Linked List Implementation public class LinkedList implements Ilist {private Node myHead; private Node myTail; private int iMySize; public LinkedList() {myHead = null; myTail = null; iMySize = 0; } LinkedList list = new LinkedList(); LinkedList myHead iMySize myTail null 0

CS 307 Fundamentals of Computer Science 8 Add Element - List Empty (Before) myHeadmyTailiMySize null 0 Object item

CS 307 Fundamentals of Computer Science 9 Add Element - List Empty (After) myHeadmyTailiMySize 1 Object Node myDatamyNext null

CS 307 Fundamentals of Computer Science 10 Add Element - List Not Empty (Before) 1 Object Node myDatamyNext null myHeadmyTailiMySize Object item

CS 307 Fundamentals of Computer Science 11 Add Element - List Not Empty (After) 2 Object Node myDatamyNext myHeadmyTailiMySize Object Node myDatamyNext null

CS 307 Fundamentals of Computer Science 12 Code for default add  public void add(Object item)

CS 307 Fundamentals of Computer Science 13 Code for arbitrary add  public void add(Object item, int pos)

CS 307 Fundamentals of Computer Science 14 Code for get  public Object get(int pos)

CS 307 Fundamentals of Computer Science 15 Code for remove  public Object remove(int pos)

CS 307 Fundamentals of Computer Science 16 Why Linked List  Are any operations with a Linked List faster than the version from ArrayList?  What about this:  public void addFront(Object item)  Big O? Array version Big O?  Fast performance for removeFront as well?

CS 307 Fundamentals of Computer Science 17 Remove Back Method  public Object removeBack()  Big O?

CS 307 Fundamentals of Computer Science 18 Other Possible Features of Linked Lists  Doubly Linked  Circular  Dummy Nodes for first and last node in list public class DLNode {private Object myData; private DLNode myNext; private DLNode myPrevious; }

CS 307 Fundamentals of Computer Science 19 Default add for Doubly Linked List  public void add(Object item)

CS 307 Fundamentals of Computer Science 20 Code for arbitrary add - Doubly Linked List  public void remove(Object item, int pos)

CS 307 Fundamentals of Computer Science 21 Code for remove Doubly Linked List  public Object remove(int pos)