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

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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

SLIDE 1

ECE242 L6: Linked Lists September 21, 2009

ECE 242 Data Structures

Lecture 6

Linked Lists

ECE242 L6: Linked Lists September 21, 2009

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

SLIDE 2

ECE242 L6: Linked Lists September 21, 2009

ArrayList Implementation - Delete An Item

Operation: delete(2)

A 1 2

maxsize-1

3 4 B C D E

Remove an item at position 2

pos A 1 2

maxsize-1

3 B D E

Count=4 pos=2 Count=5

Implementation is slow and costly Need to know max size of array

ECE242 L6: Linked Lists September 21, 2009

Another Implementation of List °Linked List b a 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

SLIDE 3

ECE242 L6: Linked Lists September 21, 2009

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

b a e null c d

Object

ECE242 L6: Linked Lists September 21, 2009

Simple Linked List °Singly Linked List (SLList)

A sequence of nodes

°Each node contains two fields

Item
Reference to next node

b a c null head Node: its value is “a”, this node also has a link which points to its succeeding node

SLIDE 4

ECE242 L6: Linked Lists September 21, 2009

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; }

ECE242 L6: Linked Lists September 21, 2009

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

node1 node2 node3 head tail

SLIDE 5

ECE242 L6: Linked Lists September 21, 2009

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

node1 node2 node3 head tail wantedNode

ECE242 L6: Linked Lists September 21, 2009

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

node1 node2 node3 head tail

SLIDE 6

ECE242 L6: Linked Lists September 21, 2009

Add New Node ° Case 1: for an empty list

set head and tail to newNode

tail newNode head ° 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

node1 node2 node3 head tail

ECE242 L6: Linked Lists September 21, 2009

head node1 node2 node3 tail Add New Node --- Case 2 (a) °(a) Insert newNode in front of head newNode head

SLIDE 7

ECE242 L6: Linked Lists September 21, 2009

Add New Node --- Case 2 (b) node1 node2 node4 tail head node3

(b) Insert newNode in the middle of list

– Suppose newNode needs to be inserted between node 2

and node 3

ECE242 L6: Linked Lists September 21, 2009

Add New Node --- Case 2 (b) newNode node1 node2 node4 tail head node3

(b) Insert newNode in the middle of list

– Suppose newNode needs to be inserted between node 2

and node 3

SLIDE 8

ECE242 L6: Linked Lists September 21, 2009

Add New Node --- Case 2 (b) node1 node2 node4 tail head node3

(b) Insert newNode in the middle of list

– Suppose newNode needs to be inserted between node 2

and node 3 newNode

ECE242 L6: Linked Lists September 21, 2009

Add New Node --- Case 2 (b) node1 node2 node4 tail head node3

(b) Insert newNode in the middle of list

– Suppose newNode needs to be inserted between node 2

and node 3 newNode

SLIDE 9

ECE242 L6: Linked Lists September 21, 2009

Add New Node --- Case 2 (c) °(c) Insert newNode after tail node2 node3 tail node1 head

ECE242 L6: Linked Lists September 21, 2009

newNode Add New Node --- Case 2 (c) °(c) Insert newNode after tail node2 node3 tail node1 head

SLIDE 10

ECE242 L6: Linked Lists September 21, 2009

newNode Add New Node --- Case 2 (c) °(c) Insert newNode after tail node2 node3 tail node1 head

ECE242 L6: Linked Lists September 21, 2009

newNode Add New Node --- Case 2 (c) °(c) Insert newNode after tail node2 node3 tail node1 head tail

SLIDE 11

ECE242 L6: Linked Lists September 21, 2009

Delete Node --- Case 2 (a)

°(a): wantedNode is both head and tail

head node 1 tail head=null tail=null after deletion

ECE242 L6: Linked Lists September 21, 2009

node2 node3 tail head node1 Delete Method --- Case 2(b) °(b): wantedNode is head, but not tail

Suppose node 1 needs to be deleted

SLIDE 12

ECE242 L6: Linked Lists September 21, 2009

Delete Method --- Case 2(b) °(b): wantedNode is head, but not tail

Suppose node 1 needs to be deleted

node2 node3 tail node1 head

ECE242 L6: Linked Lists September 21, 2009

node2 node3 tail Delete Method --- Case 2(b) °(b): wantedNode is head, but not tail head

SLIDE 13

ECE242 L6: Linked Lists September 21, 2009

Delete Method --- Case 2(c) °(c): wantedNode is not head, not tail

Suppose node2 needs to be deleted

node1 node2 node3 head tail To be deleted

ECE242 L6: Linked Lists September 21, 2009

Delete Method --- Case 2(c) °(c): wantedNode is not head, not tail

Suppose node2 needs to be deleted

node1 node2 node3 head tail To be deleted

SLIDE 14

ECE242 L6: Linked Lists September 21, 2009

Delete Method --- Case 2(c) °(c): wantedNode is not head, not tail

Suppose node2 needs to be deleted

node1 node3 head tail

ECE242 L6: Linked Lists September 21, 2009

node2 node3 tail Delete Method --- Case 2(d) °(d): wantedNode is not head, but tail head node1

SLIDE 15

ECE242 L6: Linked Lists September 21, 2009

node2 node3 tail Delete Method --- Case 2(d) °(d): wantedNode is not head, but tail head node1

ECE242 L6: Linked Lists September 21, 2009

node2 tail Delete Method --- Case 2(d) °(d): wantedNode is not head, but tail head node1

SLIDE 16

ECE242 L6: Linked Lists September 21, 2009

Summary °Size grows as needed °Data manipulation is efficient

Add, remove, etc.

ECE 242 Data Structures

Lecture 6

Linked Lists

Overview °Problem: Can we implement data structures using something other than arrays?

°Iterators will be important tools for linked lists

°Easier to implement than arrays. A little harder to visualize conceptually

ArrayList Implementation - Delete An Item

Operation: delete(2)

A 1 2

maxsize-1

3 4 B C D E

Remove an item at position 2

pos A 1 2

maxsize-1

3 B D E

Count=4 pos=2 Count=5

Implementation is slow and costly Need to know max size of array

Another Implementation of List °Linked List b a c null °Take as much memory as needed

°No need to move items around

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

b a e null c d

Object

Simple Linked List °Singly Linked List (SLList)

°Each node contains two fields

b a c null head Node: its value is “a”, this node also has a link which points to its succeeding node

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; }

Singly Linked List --- head/tail °Important variables in Singly Linked List

Indicates the beginning of the List

Indicates the end of the List

node1 node2 node3 head tail

Search() Method In Listed Link ° For an empty list, return empty list ° For a nonempty list

node1 node2 node3 head tail wantedNode

Size() Method In Listed Link ° For an empty list, return size 0 ° For a nonempty list

node1 node2 node3 head tail

Add New Node ° Case 1: for an empty list

tail newNode head ° Case 2: for a non-empty list, find where newNode should be inserted

node1 node2 node3 head tail

head node1 node2 node3 tail Add New Node --- Case 2 (a) °(a) Insert newNode in front of head newNode head

Add New Node --- Case 2 (b) node1 node2 node4 tail head node3

– Suppose newNode needs to be inserted between node 2

and node 3

Add New Node --- Case 2 (b) newNode node1 node2 node4 tail head node3

– Suppose newNode needs to be inserted between node 2

and node 3

Add New Node --- Case 2 (b) node1 node2 node4 tail head node3

– Suppose newNode needs to be inserted between node 2

and node 3 newNode

Add New Node --- Case 2 (b) node1 node2 node4 tail head node3

– Suppose newNode needs to be inserted between node 2

and node 3 newNode

Add New Node --- Case 2 (c) °(c) Insert newNode after tail node2 node3 tail node1 head

newNode Add New Node --- Case 2 (c) °(c) Insert newNode after tail node2 node3 tail node1 head

newNode Add New Node --- Case 2 (c) °(c) Insert newNode after tail node2 node3 tail node1 head

newNode Add New Node --- Case 2 (c) °(c) Insert newNode after tail node2 node3 tail node1 head tail

Delete Node --- Case 2 (a)

°(a): wantedNode is both head and tail

head node 1 tail head=null tail=null after deletion

node2 node3 tail head node1 Delete Method --- Case 2(b) °(b): wantedNode is head, but not tail

Delete Method --- Case 2(b) °(b): wantedNode is head, but not tail

node2 node3 tail node1 head

node2 node3 tail Delete Method --- Case 2(b) °(b): wantedNode is head, but not tail head

Delete Method --- Case 2(c) °(c): wantedNode is not head, not tail

node1 node2 node3 head tail To be deleted

Delete Method --- Case 2(c) °(c): wantedNode is not head, not tail

node1 node2 node3 head tail To be deleted

Delete Method --- Case 2(c) °(c): wantedNode is not head, not tail

node1 node3 head tail

node2 node3 tail Delete Method --- Case 2(d) °(d): wantedNode is not head, but tail head node1

node2 node3 tail Delete Method --- Case 2(d) °(d): wantedNode is not head, but tail head node1

node2 tail Delete Method --- Case 2(d) °(d): wantedNode is not head, but tail head node1

Summary °Size grows as needed °Data manipulation is efficient

°Linked List implementation is more efficient than array °We will lots more implementations and uses of linked lists in subsequent lectures