ECE 242 Data Structures Lecture 6 Linked Lists September 21, 2009 - PDF document

ECE 242 Data Structures Lecture 6 Linked Lists September 21, 2009 ECE242 L6: Linked Lists Overview ° Problem: Can we implement data structures using something other than arrays? • Individual objects can be more flexible • Use references to find “neighbors” ° Iterators will be important tools for linked lists • Search through the list ° Easier to implement than arrays. A little harder to visualize conceptually September 21, 2009 ECE242 L6: Linked Lists

ArrayList Implementation - Delete An Item Operation: delete(2) maxsize-1 maxsize-1 Count=5 Count=4 4 E Remove an item D E 3 3 pos=2 pos at position 2 2 C 2 D 1 B 1 B 0 A 0 A Implementation is slow and costly Need to know max size of array September 21, 2009 ECE242 L6: Linked Lists Another Implementation of List ° Linked List a b c null ° Take as much memory as needed • no more and no less • allocate the memory dynamically if needed ° No need to move items around September 21, 2009 ECE242 L6: Linked Lists

Advantage of Linked List ° Nodes can be located anywhere in the memory. ° Getting from one node to another by storing the reference of the next node ° Insertion/removal does not require moving other items Object a b c d e null September 21, 2009 ECE242 L6: Linked Lists Simple Linked List ° Singly Linked List (SLList) • A sequence of nodes ° Each node contains two fields • Item • Reference to next node a b c null head Node: its value is “a”, this node also has a link which points to its succeeding node September 21, 2009 ECE242 L6: Linked Lists

Node Definition ° Define an abstract object Node: private class Node { private Object item; Node next; } ° Example for Employee Node: private class Node { Employee e; Node next; } September 21, 2009 ECE242 L6: Linked Lists Singly Linked List --- head/tail ° Important variables in Singly Linked List • head Indicates the beginning of the List • tail Indicates the end of the List tail head node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists

Search() Method In Listed Link ° For an empty list, return empty list ° For a nonempty list • Search for the wantedNode from head, print the record if matched tail head wantedNode node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists Size() Method In Listed Link ° For an empty list, return size 0 ° For a nonempty list • count the total number of nodes in the Linked List tail head node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists

Add New Node ° Case 1: for an empty list • set head and tail to newNode head newNode tail ° Case 2: for a non-empty list, find where newNode should be inserted • (a) insert in front of head • (b) insert in the middle of list • (c) insert after tail tail head node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists Add New Node --- Case 2 (a) ° (a) Insert newNode in front of head tail head head newNode node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists

Add New Node --- Case 2 (b) • (b) Insert newNode in the middle of list – Suppose newNode needs to be inserted between node 2 and node 3 tail head node1 node2 node3 node4 September 21, 2009 ECE242 L6: Linked Lists Add New Node --- Case 2 (b) • (b) Insert newNode in the middle of list – Suppose newNode needs to be inserted between node 2 and node 3 tail head node1 node2 node3 node4 newNode September 21, 2009 ECE242 L6: Linked Lists

Add New Node --- Case 2 (b) • (b) Insert newNode in the middle of list – Suppose newNode needs to be inserted between node 2 and node 3 tail head node1 node2 node3 node4 newNode September 21, 2009 ECE242 L6: Linked Lists Add New Node --- Case 2 (b) • (b) Insert newNode in the middle of list – Suppose newNode needs to be inserted between node 2 and node 3 tail head node1 node2 node3 node4 newNode September 21, 2009 ECE242 L6: Linked Lists

Add New Node --- Case 2 (c) ° (c) Insert newNode after tail head tail node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists Add New Node --- Case 2 (c) ° (c) Insert newNode after tail head tail node1 node2 node3 newNode September 21, 2009 ECE242 L6: Linked Lists

Add New Node --- Case 2 (c) ° (c) Insert newNode after tail head tail node1 node2 node3 newNode September 21, 2009 ECE242 L6: Linked Lists Add New Node --- Case 2 (c) ° (c) Insert newNode after tail head tail tail node1 node2 node3 newNode September 21, 2009 ECE242 L6: Linked Lists

Delete Node --- Case 2 (a) ° (a): wantedNode is both head and tail head head=null after deletion node 1 tail tail=null September 21, 2009 ECE242 L6: Linked Lists Delete Method --- Case 2(b) ° (b): wantedNode is head, but not tail • Suppose node 1 needs to be deleted tail head node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists

Delete Method --- Case 2(b) ° (b): wantedNode is head, but not tail • Suppose node 1 needs to be deleted tail head node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists Delete Method --- Case 2(b) ° (b): wantedNode is head, but not tail tail head node2 node3 September 21, 2009 ECE242 L6: Linked Lists

Delete Method --- Case 2(c) ° (c): wantedNode is not head, not tail • Suppose node2 needs to be deleted tail head node1 node2 node3 To be deleted September 21, 2009 ECE242 L6: Linked Lists Delete Method --- Case 2(c) ° (c): wantedNode is not head, not tail • Suppose node2 needs to be deleted tail head node1 node2 node3 To be deleted September 21, 2009 ECE242 L6: Linked Lists

Delete Method --- Case 2(c) ° (c): wantedNode is not head, not tail • Suppose node2 needs to be deleted tail head node1 node3 September 21, 2009 ECE242 L6: Linked Lists Delete Method --- Case 2(d) ° (d): wantedNode is not head, but tail tail head node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists

Delete Method --- Case 2(d) ° (d): wantedNode is not head, but tail tail head node1 node2 node3 September 21, 2009 ECE242 L6: Linked Lists Delete Method --- Case 2(d) ° (d): wantedNode is not head, but tail tail head node1 node2 September 21, 2009 ECE242 L6: Linked Lists

Summary ° Size grows as needed ° Data manipulation is efficient • Add, remove, etc. ° Linked List implementation is more efficient than array ° We will lots more implementations and uses of linked lists in subsequent lectures September 21, 2009 ECE242 L6: Linked Lists