preparation data structures 05 chain linear_list

Data StructuresIterators and Chain Linear List

Andres Mendez-Vazquez

May 6, 2015

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Images/cinvestav-1.jpg

Outline1 Iterators

InterfaceSeparate and Inner Class Iterator

2 IntroductionLinked RepresentationMemory Layout

3 OperationsIsEmpty()size()Get(Index)RemoveAdd

4 Can we simplify the code?

5 Other data structures based in the Linked List

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Iterator Method

ScenarioWe often want to access every item in a data structure or collection inturn...

Example with the array representation1 int listSize = SomeList.size();2 for (int i = 0; i < listSize; i++)3 System.out.println(SomeList.get(i));

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Iterator Method

ScenarioWe often want to access every item in a data structure or collection inturn...

Example with the array representation1 int listSize = SomeList.size();2 for (int i = 0; i < listSize; i++)3 System.out.println(SomeList.get(i));

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Motivation

QuestionWhat if we have a get that is really complex?

For example the get in a Chain ListWe will see that it has complexity O(n)!!!

Previous CodeWhat a waste of time!!! O

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Motivation

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Motivation

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Something NotableIteration is such a common operation that we could include it as part ofthe ADT list.

HoweverWe do not want to add another operation to the ADT each time we thinkof another way to use an iteration.

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Something NotableIteration is such a common operation that we could include it as part ofthe ADT list.

HoweverWe do not want to add another operation to the ADT each time we thinkof another way to use an iteration.

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Outline1 Iterators

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In Java at java.util we have the interface Iterator

Interface

package j a v a . u t i l ;p u b l i c i n t e r f a c e I t e r a t o r <Item> {

p u b l i c boo l ean hasNext ( ) ;

p u b l i c I tem next ( ) ;

// Opt i ona l methodp u b l i c vo i d remove ( ) ;

} // end I t e r a t o r

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Explanation

public boolean hasNext()It detects whether this iterator has completed its traversal and gonebeyond the last entry in the collection of data.It returns true if the iterator has another entry to return.

public T next()It retrieves the next entry in the collection and advances this iteratorby one position.It returns a reference to the next entry in the iteration, if one existsIt throws NoSuchElementException if the iterator had reached theend already, that is, if hasNext() is false.

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Explanation

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Explanation

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Explanation

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Explanation

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Explanation

public void remove()It removes from the collection of data the last entry that next()returned.Precondition: next() has been called, and remove() has not been

called since then.I It throws IllegalStateException if next() has not been

called, or if remove() was called already after the lastcall to next().

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Explanation

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Explanation

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Effect in a list

Before next()Joes Piotor Iterator cursor Jen Jess Marius

After next()Joes Piotor Jen Iterator cursor Jess Marius

Effect of remove()Joes Piotor Iterator cursor Jess Marius

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Effect in a list

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Effect in a list

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NO FREE LUNCH!!!

RemarkSome details of using an iterator depend on the approach used toimplement the iterator methods.

We can do the followingA possible, but not optimal, way to provide an ADT with traversaloperations is to define them as ADT operations.

I For example, if ListInterface extends Iterator, a list object wouldhave iterator methods as well as list methods.

I PROBLEM!!! What if you want to have two or more iterators over theobject list making different things at the same time!!!

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NO FREE LUNCH!!!

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NO FREE LUNCH!!!

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NO FREE LUNCH!!!

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Outline1 Iterators

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Solution

We can haveSeparate class iteratorInner Class Iterator

For separate class iterator, we have stuff like thisIterator<String> nameIterator = newSeparateIterator<String>(nameList);

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Solution

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Solution

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Example

Problem Number of times Any Name Appears in the list

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Multiple Iterators

ThusExternal Iterators provides a solution to multiple iterators

However

Huge ProblemWe can only access the list through the public methods:

What if they are not enough?

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Multiple IteratorsThusExternal Iterators provides a solution to multiple iterators

However

Object Iterator from separate class iterators

Object from class list

LouPegMegME

IteratorCursor

NextPosition2

Huge ProblemWe can only access the list through the public methods:

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Separate Iterator CodeCode

impor t j a v a . u t i l . I t e r a t o r ;impor t j a v a . u t i l . NoSuchElementExcept ion ;

p u b l i c c l a s s S e p a r a t e I t e r a t o r <Item>implements I t e r a t o r <Item> {

p r i v a t e L i n e a r L i s t <Item> l i s t ;// p o s i t i o n o f e n t r y l a s t r e t u r n e d by next ( )p r i v a t e i n t n e x t P o s i t i o n ;// needed by removep r i v a t e boo l ean wasNextCa l l ed ;

p u b l i c S e p a r a t e I t e r a t o r ( L i s t L i s t <Item> aL i s t ) {// A l l t ha t i t i m p l i e s} // end c o n s t r u c t o r

< Imp l ementa t i on s o f the methods hasNext , . . .nex t , and remove go he r e > . . .} // end S e p a r a t e I t e r a t o r

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We need a better solution!!!

Declare a inner classSo you can have direct access to the protected or private elements in theobject!!!

Actually you have something like this

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We need a better solution!!!

Declare a inner classSo you can have direct access to the protected or private elements in theobject!!!

Actually you have something like this

Object Iterator from Inner class iterators

Object from class array list

Lou Peg Meg ME

nextPosition2

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Inner Class Code

Codeimpor t j a v a . u t i l . I t e r a t o r ;impor t j a v a . u t i l . NoSuchElementExcept ion ;

p u b l i c c l a s s A r r a y L i s t W i t h I t e r a t o r <T>implements L i s t W i t h I t e r a t o r I n t e r f a c e <T> {

// ALL the code f o r a r r a y l i n e a r l i s t

p r i v a t e c l a s s I t e r a t o r F o r A r r a y L i s timp lements I t e r a t o r <T> {

p r i v a t e i n t n e x t I n d e x ;p r i v a t e boo l ean wasNextCa l l ed ;

p r i v a t e I t e r a t o r F o r A r r a y L i s t ( ) {n e x t I n d e x = 0 ;wasNextCa l l ed = f a l s e ;

} // end d e f a u l t c o n s t r u c t o r

< I m p l e m e n t a t i o n s o f the methods i n thei n t e r f a c e I t e r a t o r go he r e > . . . }// end I t e r a t o r F o r A r r a y L i s t

} // end A r r a y L i s t W i t h I t e r a t o r

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So, we have...

AdvantagesIt is a way of logically grouping classes that are only used in one place.It increases encapsulationIt can lead to more readable and maintainable code.

ExampleArrayListWithIterator<Integers> SOME = newArrayListWithIterator<Integers>();ArrayListWithIterator.IteratorForArrayList fl = SOME. newIteratorForArrayList();

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So, we have...

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So, we have...

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So, we have...

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Outline1 Iterators

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Linked Representation

StorageList elements are stored, in memory, in an arbitrary order.

How you move through itExplicit information (called a link) is used to go from one element to thenext.

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Linked Representation

StorageList elements are stored, in memory, in an arbitrary order.

How you move through itExplicit information (called a link) is used to go from one element to thenext.

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Outline1 Iterators

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Memory Layout

We have the following

C A E D B

firstNode

FirstLast pointer (or link) from E is null

ThusYou can use a variable firstNode to get to the first element in the LinkedList.

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Memory Layout

C A E D B

firstNode

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Memory Layout

C A E D B

firstNode

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Normal Way To Draw A Linked List

Example

CA EDB

firstNode

Link or pointer field of node

Data field of node

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Actually, we know this as a Chain

FirstA chain is a linked list in which each node represents one element.

SecondThere is a link or pointer from one element to the next.

ThirdThe last node has a null pointer.

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Code for ChainNode

package L i n e a r L i s t ;// Us ing Gene r i c i n Javac l a s s ChainNode<Item>{

// package data membersp r o t e c t e d Item e lement ;p r o t e c t e d ChainNode next ;// c o n s t r u c t o r s and methods come he r e

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The Constructors for ChainNode

A classic one

package L i n e a r L i s t ;// Us ing Gene r i c i n Javap u b l i c ChainNode ( ){

// Set the next nodet h i s . e l ement = n u l l ;t h i s . nex t = n u l l ;

p u b l i c ChainNode ( Item elem ){// Set e l ementt h i s . e l ement = elem ;t h i s . nex t = n u l l ;

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What about the Class Chain?

/∗∗ l i n k e d imp l ementa t i on o f L i n e a r L i s t ∗/package i n f r a s t r u c t u r e s ;impor t j a v a . u t i l . ∗ ; // has I t e r a t o rp u b l i c c l a s s Chain<Item> implements L i n e a r L i s t <Item>{// data membersp r o t e c t e d ChainNode<Item> f i r s tN o d e ;p r o t e c t e d i n t s i z e ;

// methods o f Chain come he r e}

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In addition!!! Constructors!!!Code

p u b l i c Chain<Item> ( i n t i n i t i a l C a p a c i t y ){

// the d e f a u l t i n i t i a l v a l u e s o f f i r s t N o d e and s i z e// a r e n u l l and 0 , r e s p e c t i v e l y

A simple examplepublic Chain<Item> ()

{this.firstNode = new ChainNode<Item>();this.size = 0;

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In addition!!! Constructors!!!Code

p u b l i c Chain<Item> ( i n t i n i t i a l C a p a c i t y ){

// the d e f a u l t i n i t i a l v a l u e s o f f i r s t N o d e and s i z e// a r e n u l l and 0 , r e s p e c t i v e l y

A simple examplepublic Chain<Item> ()

{this.firstNode = new ChainNode<Item>();this.size = 0;

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Outline1 Iterators

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IsEmpty()

Really Simple Code

/∗∗ @re tu rn t r u e i f f l i s t i s empty ∗/p u b l i c boo l ean isEmpty ( )

{ r e t u r n s i z e == 0 ;}

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Outline1 Iterators

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size()

Really Simple Code

/∗∗ @re tu rn c u r r e n t number o f e l ement s i n l i s t ∗/p u b l i c i n t s i z e ( )

{ r e t u r n s i z e ; }

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Outline1 Iterators

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Operations: Get

Example

CA EDB

firstNode

Data field of node

What to do to implement Get1 Check Index2 Move to the correct position

I For example: TempNode = firstNode.next.next.next.I You actually use a loop.

3 return TempNode.element

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Operations: Get

Example

CA EDB

firstNode

Data field of node

What to do to implement Get1 Check Index2 Move to the correct position

I For example: TempNode = firstNode.next.next.next.I You actually use a loop.

3 return TempNode.element

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Process

Check Index

0 ≤ index ≤ size − 1 (1)

Negate the statement to use itHow?

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Process

Check Index

0 ≤ index ≤ size − 1 (1)

Negate the statement to use itHow?

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Move to the correct place

CA EDB

firstNode NULL

TempNode=firstNode

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Index == 2

CA EDB

firstNode NULL

TempNode=firstNode

index==2

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Index == 2

CA EDB

firstNode NULL

TempNode=TempNode.next

index==2

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Index == 2

CA EDB

firstNode NULL

TempNode=TempNode.next

index==2

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Index == 2

CA EDB

firstNode NULL

return TempNode.element

index==2

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Here is the method

p u b l i c <Item> get ( i n t i nd ex ){ChainNode<Item> TempNode ;// Check a lwaysi f ( t h i s . s i z e == 0) r e t u r n n u l l ;i f ( index <0 | | index>t h i s . s i z e −1){

System . out . p r i n t l n ( " I ndex ␣ out ␣ o f ␣bound " ) ;System . e x i t ( 0 ) ;

}//Move to the c o r r e c t p o s i t i o nTempNode = t h i s . f i r s t N o d e ;f o r ( i n t i=0 ; i<i ndex ; i ++){

TempNode = TempNode . nex t ;}r e t u r n TempNode . e l ement ;

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Outline1 Iterators

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Now, Remove

We have two casesAny ideas?

Case IRemoving from the beginning.

Case IIRemove from the middle.

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Now, Remove

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Now, Remove

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Case I: Remove(0)

Process1 if index == 0 do

1 TempNode = firstNode2 firstNode=firstNode.next3 TempNode.next=NULL4 return TempNode.element

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Case I: Remove(0)

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Case I: Remove(0)

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Case I: Remove(0)

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Case I: Remove(0)

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Process

TempNode=firstNode

CA EDB

firstNode NULL

TempNode=firstNode

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Process

firstNode=firstNode.next

CA EDB

firstNode NULL

TempNode

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Process

TempNode.next=NULL

CA EDB

firstNode NULL

TempNode NULL

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Process

return TempNode.element

CA EDB

firstNode NULL

return TempNode.elementNULL

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Case II: Remove(2)

Process1 Check Index2 Starting at the first node3 TempNode=firstNode;4 Loop doing

1 beforeNode=TempNode;2 TempNode=TempNode.next;

5 before.next = TempNode.next6 TempNode.next = NULL7 return TempNode.element

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Case II: Remove(2)

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Case II: Remove(2)

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Case II: Remove(2)

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Case II: Remove(2)

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Case II: Remove(2)

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Case II: Remove(2)

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Case II: Remove(2)

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Case II: Remove(2)

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Process

TempNode=firstNode

CA EDB

firstNode NULL

TempNode=firstNode

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Process: index == 2

beforeNode=TempNode;TempNode=TempNode.next;

CA EDB

firstNode NULL

beforeNode=TempNode TempNode=TempNode.next

index==2

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Process: index == 2

beforeNode=TempNode;TempNode=TempNode.next;

CA EDB

firstNode NULL

beforeNode=TempNode TempNode=TempNode.next

index==2

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Process: index == 2

before.next = TempNode.next

CA EDB

firstNode NULL

beforeNode.next=TempNode.next

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Process: index == 2

TempNode.next = NULL

CA EDB

firstNode NULL

TempNode=TempNode.nextNULL

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Process: index == 2

TempNode.next = NULL

CA EDB

firstNode NULL

return TempNode.elementNULL

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Outline1 Iterators

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Now, Add

We have four casesAny ideas?

Case IThe Chain is Empty

Case IIAdd at the beginning.

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Now, Add

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Now, Add

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Now, Add

Case IIIAdd at the middle.

Case IVAdd at the end.

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Now, Add

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Now, Add

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Think About it!!!Remember you have a sequential access.

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Add at an empty list

Steps1 Create a node to store the element, NewNode2 Then assign firstNode = NewNode

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firstNode

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Add At the Beginning

Steps1 Create a node to store the element, NewNode2 Do NewNode.next = firstNode3 Then reassign firstNode = NewNode4 Then, size = size +1

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CA EDB

firstNode

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What about the other case?

Do you have an idea?Add at the Middle.Add at the end.

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What about the other methods?

Linear ListAbstractDataType LinearList{

instancesordered finite collections of zero or more elements

operationsisEmpty(): return true iff the list is empty, false otherwisesize(): return the list size (i.e., number of elements in the list)get(index): return the element with the “index” indexindexOf(x): return the index of the first occurrence of x in the list, return -1

if x is not in the listremove(index): remove and return the indexth element, elements with higher

index have their index reduced by 1add(theIndex, x): insert x as the index of th element, elements with

theIndex ≥ index have their index increased by 1output(): output the list elements from left to right

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Complexity of Linked List

We haveDynamic Array Linked List

Amortized AnalysisIndexing O (1) O (n)Search O (n) O (n)

Add/Remove at the beginning O (n) O (1)Add/Remove at the middle O (n) Search Time

+O (1)Space Complexity O (n) O (n)

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Average Performance with Each Implementation on a SlowMachine!!!

40,000 Operations each type on a 350Mhz PCOperation FastArrayLinearList Chainaverage get 5.6 ms 157 secaverage adds 5.8 sec 115 sec

average removes 5.8 sec 157 sec

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Can we simplify the code?

How?We would like to simplify the code.... How?

What about

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How?We would like to simplify the code.... How?

What about

CA EDBheaderNode NULL

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Then, the empty list looks likeheaderNode

ThusThis simplify a lot the code because everything is a middle node

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Then, the empty list looks likeheaderNode

ThusThis simplify a lot the code because everything is a middle node

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Circular List

CA EDB

firstNode lastNode

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Here, we need to have the following changes

We need to add the following to the class

/∗∗ l i n k e d imp l ementa t i on o f L i n e a r L i s t ∗/package i n f r a s t r u c t u r e s ;impor t j a v a . u t i l . ∗ ; // has I t e r a t o rp u b l i c c l a s s Chain<Item> implements L i n e a r L i s t <Item>{// data membersp r o t e c t e d ChainNode<Item> f i r s tN o d e ;p r o t e c t e d ChainNode<Item> la s tNode ;p r o t e c t e d i n t s i z e ;

// methods o f Chain come he r e}

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Example of add(index) at the end

ProcessCheck if (index==size-1)

NextMake the lastNode.next = TempNode

ThenTempNode.next = firstNode

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FinallylastNode = TempNode

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Circular List

Add at the end

CA EDB

firstNode lastNode

lastNode.next = TempNode

TempNode

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Circular List

Add at the end

CA EDB

firstNode

lastNode

TempNode.next = firstNode TempNode

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Circular List

Add at the end

CA EDB

firstNode

lastNode=TempNode

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We have other representations for the lists

Doubly Linked ListYou have two chain list going through the nodes.It has a firstNodeIt has a lastNode

Doubly Linked Circular ListYou have two chain list going through the nodes.It has a firstNode

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We have other representations for the lists

Doubly Linked ListYou have two chain list going through the nodes.It has a firstNodeIt has a lastNode

Doubly Linked Circular ListYou have two chain list going through the nodes.It has a firstNode

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Doubly Linked List

CA EDB

firstNode lastNode

What about the changes here

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Doubly Linked Circular List

CA EDB

firstNode

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Where does Java has all these things?

Packagejava.util.LinkedList

There you haveIt has the Linked implementation of a linear list.It has the doubly linked circular list with header node.It Has all methods of LinearList plus many more.

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preparation data structures 05 chain linear_list

Education

i c item

i c void

c e i t e r

i c i n t e r f

chain list

linked list

adt list

i c boolean hasnext