Chapter 5 Linked Lists Dr. Youssef Harrath yharrath@uob.edu.bh.

transcript

Chapter 5

Linked Lists

Dr. Youssef Harrath

yharrath@uob.edu.bh

Outline

1. Introduction

2. Properties

3. Insertion and Deletion

4. Building a Linked List

5. Linked List As an ADT

6. Ordered Linked Lists

7. Doubly Linked Lists

8. Linked Lists with Header and Trailer Nodes

9. Circular Linked Lists

2Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

1. Introduction

A linked list is a collection of components, called nodes.

Every node (except the last node) contains the address of the

next node.

Every node has two components: data to store the relevant

information, and link to store the address of the next node.

info link

Structure of a node

struct nodeType

int info;

nodeType *link;

1. Introduction

92 9317 45

head node1 node4node3node2

92 1500 63 360017 2800 45 0head

2000 360015002800

node1 node4node3node2

Memory locations

2. Properties

92 1500 63 360017 2800 45 0

head 2000 360015002800

info linkinfoinfoinfo linklink link

Variable

head->info

head->link

head->link->info

2. Properties

Variable

current

current->info

current->link

current->link->info

nodeType *current;

current = head;

current

92 1500 63 360017 2800 45 0

head 2000 360015002800

2. Properties

current

92 1500 63 360017 2800 45 0

head 2000 360015002800

current

92 1500 63 360017 2800 45 0

head 2000 360015002800

current = current->link;

current 2800

current->info 92

current->link 1500

current->link->info 63

2. Properties

current

92 1500 63 360017 2800 45 0

head 2000 360015002800

head->link->link 1500

head->link->link->info 63

head->link->link->link 3600

head->link->link->link->info 45

current->link->link 3600

current->link->link->info 45

current->link->link->link 0 (that is, NULL)

current->link->link->link->info Does not exist

2. Properties: Traversing a Linked List

The basic operations of a linked list are:

Search the list to determine whether a particular item is in the list.

Insert an item in the list.

Delete an item from the list.

The operations require the list to be traversed.

current = head; // To keep head pointing always the first node.

while(current != NULL)

// Process current

2. Properties: Traversing a Linked List

current = head;

while(current != NULL) // to output the elements of the linked list

cout<<current->info<<" ";

current

92 1500 63 360017 2800 45 0

head 2000 360015002800

3. Insertion And Deletion: Insertion

struct nodeType{int info;nodeType *link;};…nodeType *head, *p, *q, *newNode;

65 3445 76head

pnewNode = new nodeType;

newNode->info = 50;

65 3445 76head

p50newNode

newNode = new nodeType;

newNode->info = 50;

65 3445 76head

p50newNode

newNode->link = p->link;

p->link = newNode;

65 3445 76head

newNode

What happen if we inverse the order of the two statements?

p->link = newNode;

newNode->link = p->link;

65 3445 76head

newNode

p->link = newNode;

Using two pointers, we can simplify the insertion code.

65 3445 76head

newNode

p->link = newNode;

newNodep->link = q ;

The order of the two statements is not important.

p->link = newNode;

newNodep->link = q ;

3. Insertion And Deletion: Deletion

Consider the following linked list. Suppose that the node with

info 34 is to be deleted from the list.

p->link = p->link->link; // the link of the node with info 65 will point the node with info 76

65 3445 76head

pThe node still in memory

3. Insertion And Deletion: Deletion

To delete the node with info 34 from the list and deallocate the

memory occupied by this node:

q = p->link;

p->link = q->link;

delete q;

6545 76head

65 3445 76head

4. Building a Linked List: Forward

nodeType *first, *last, *newNode;int num;first = NULL; // to point the first nodelast = NULL; // to point the last nodecin>>num;newNode = new nodeType; // Fill the newNode fields newNode->info = num;newNode->info = num;newNode->link = NULL;newNode->link = NULL;if(first == NULL) // empty list{first = newNode;first = newNode;last = newNode;last = newNode;}else // to insert a node at the end of the list{last->link = newNode;last->link = newNode;last = newNode;last = newNode;}

Exercise: Write a function named

buildListForward() with no parameter to

build a linked list (with many integers) and

returns a pointer to the first element. Each

new element has to be inserted at the end

of the list.

// SolutionnodeType * buildListForward()

nodeType *first, *last, *newNode;

int num;

cout<<"Enter a list of integers ending by -1: ";

cin>>num;

first = NULL; // to point the first node

// here a loop to read many elements terminated by -1

return first;

while(num != -1) // the loop{newNode = new nodeType;assert(newNode != NULL);newNode->info = num;newNode->link = NULL;if(first == NULL) // empty list{first = newNode;last = newNode;}else // to insert a node at the end of the list{last->link = newNode;last = newNode;}cin>>num;} // end while

4. Building a Linked List: Backwards

Algorithm to insert a new node at the beginning of linked list:

1.Initialize first to NULL.

2.For each item in the list:

A. Create the new node, newNode.

B. Store the item in newNode ().

C. Inset newNode before first.

D. Update the value of the pointer first

Question: convert the above algorithm to C++ code.

4. Building a Linked List: Backwards

// Solution

nodeType* buildListBackward(){

nodeType *first, *newNode;int num;cout<<"Enter a list of integers ending by -1: ";cin>>num;first = NULL; // to point the first node

while(num != -1){

newNode = new nodeType;assert(newNode != NULL);newNode->info = num;newNode->link = first;first = newNode;cin>>num;

} // end whilereturn first;

Starting from this section, the linked lists will be treated as an ADT by the

use of templates (general type will be used for the info field).

The basic operations on linked lists are:

1. Initialize the list7. Retrieve the info contained in the last node

2. Check whether the list is empty 8. Search the list for a given item

3.Output the list 9. Insert an item in the list

4. Find the length of the list 10. Delete an item from the list

5. Destroy the list 11. Make a copy of the linked list

6. Retrieve the info contained in the first node

template<class Type> // Part Istruct nodeType{

Type info;nodeType<Type> *link;

};template<class Type>class linkedListType{

friend ostream& operator<<(ostream&, const linkedListType<Type>&);public:

const linkedListType<Type>& operator=(const linkedListType<Type>&);void initializeList();bool isEmtyList();int length();

void destroyList(); // Part IIType front();Type back();bool serach(const Type& searchItem);void insertFirst(const Type& newItem);void insertLast(const Type& newItem);void deleteNode(const Type& deleteItem);linkedListType();linkedListType(const linkedListType<Type>& otherList);~linkedListType();

protected:int count;nodeType<Type> *first;nodeType<Type> *last;

private:void copyList(const linkedListType<Type> otherList);

info link info link info link

linkedListType<Type> list;

node1 node2 nodecount

nodeType<Type> objects

5. Linked List As an ADT: Remarks

The data members of the class linkedListType are protected , not private,

because other classes will be derived from this class.

The function copyList is declared private because we use this function

only to implement the copy constructor and the function to overload the

assignment operator.

The definition of the class linkedListType includes a member function to

overload the assignment operator. This must be done for every class

including pointer data members.

For the same reason, the class linkedListType includes a copy

constructor.

5. Linked List As an ADT: isEmptyList() and default Constructor

template<class Type>

bool linkedListType<Type>::isEmtyList()

return(first == NULL);

linkedListType<Type>::linkedListType()

first = NULL;

last = NULL;

count = 0;

5. Linked List As an ADT: destroyList()

65 3445 76first

temp last

65 3445 76first

temp last

65 34 76first

5. Linked List As an ADT: destroyList()

void linkedListType<Type>::destroyList()

nodeType<Type> *temp;

while(first != NULL)

temp = first;

first = first->link;

delete temp;

last = NULL;

count = 0;

5. Linked List As an ADT: initializeList()

void linkedListType<Type>::initializeList()

destroyList();

5. Linked List As an ADT: << operator

ostream& operator<<(ostream& osObject, const linkedListType<Type>& list)

nodeType<Type> *current; // pointer to traverse the list

current = list.first;

osObject<<current->info<<" ";

return osObject;

5. Linked List As an ADT: length() and front()

int linkedListType<Type>::length()

return count;

Type linkedListType<Type>::front()

assert(last != NULL);

return first->info;

5. Linked List As an ADT: back()

Type linkedListType<Type>::back()

assert(last != NULL);

return last->info;

5. Linked List As an ADT: searchItem()

Algorithm

The member function search searches for a given item. If the item is

found, it returns true. The search must start from the first node.

1. Compare the search item with the current node in the list. If

the info of the current node is the same as the search item,

stop the search; otherwise, make the next node the current

2. Repeat step 1 until either the item is found or no more data is

left in the list to compare with the search item.

5. Linked List As an ADT: searchItem()

bool linkedListType<Type>::search(const Type& searchItem)

nodeType<Type> *current;

bool found;

current = first;

found = false;

while(current != NULL && !found)

if(current->info == searchItem)

found = true;

return found;

5. Linked List As an ADT: insertFirst()

Algorithm

The member function insertFirst inserts the new item at the

beginning of the list. The Algorithm is:

1. Create a new node.

2. If unable to create the node, terminate the program.

3. Store the new item in the new node.

4. Insert the node before first.

5. Increment count by 1.

5. Linked List As an ADT: insertFirst()

void linkedListType<Type>::insertFirst(const Type& newItem)

nodeType<Type> *newNode;

newNode = new nodeType<Type>;

assert(newNode != NULL);

newNode->info = newItem;

newNode->link = first;

first = newNode;

count++;

if(last == NULL)

last = newNode;

5. Linked List As an ADT: insertLast()

template<class Type>void linkedListType<Type>::insertLast(const Type& newItem){

nodeType<Type> *newNode;newNode = new nodeType<Type>;assert(newNode != NULL);newNode->info = newItem;newNode->link = NULL;if(first == NULL){

first = newNode;last = newNode;

}else{

last->link = newNode;last = newNode;

}count++;

5. Linked List As an ADT: deleteNode()

Case1:deleteNode(10)

Case2: deleteNode(10)

count 0

count 3

10 34 76

Case4: deleteNode(10)

count 3

25 34 76

Case3: deleteNode(34) or deleteNode(76)

count 3

10 34 76

5. Linked List As an ADT: deleteNode(): ALGORITHM

if the list is empty

Output(cannot delete from an empty list);

if the first node is the node with the given info,

adjust first, last (if necessary), count, and deallocate the memory;

search the list for the node with the given info

if such a node is found, delete it and adjust the values of last (if necessary),

and count.

5. Linked List As an ADT: deleteNode()

Program

5. Linked List As an ADT: copyList()

Algorithm

• copyList makes an identical copy of a linked list.

• We traverse the list to be copied starting from the first node.

• For each node in the original list, we:

1. Create a new node.

2. Copy the info of the node (in the original list) into the new

3. Insert the new node at the end of the list being created.

5. Linked List As an ADT: copyList()

Program

5. Linked List As an ADT: Destructor and Copy Constructor

linkedListType<Type>::~linkedListType() //destructor

destroyList();

linkedListType<Type>::linkedListType(const linkedList<Type>& otherList)

first = NULL;

copyList(otherList);

5. Linked List As an ADT: Overloading the Assignment Operator

const linkedListType<Type>& linkedListType<Type> ::operator=

(const linkedListType<Type>& otherList)

if(this != &otherList) //avoid self-copy

copyList(otherList);

return *this;

This section discusses how to build ordered linked list

The basic operations on linked lists are:

1. Initialize the list 6. Search the list for a given item

2. Check whether the list is empty 7. Insert an item in the list

3.Output the list 8. Delete an item from the list

4. Output the list 9. Find the length of the list

5. Destroy the list 10. Make a copy of the list

class orderedLinkedListType: public

linkedListType<Type>

public:

bool serach(const Type& searchItem);

void insertNode(const Type& newItem);

void deleteNode(const Type& newItem);

6. Ordered Linked Lists: Remarks

The class orderedLinkedListType is derived from the class

linkedListType.

The elements of the ordered list are to be ordered according to a criteria.

Some functions can be used from the class linkedListType (like

insertFirst and insertLast.

No need for the pointer last (it is set to NULL) because the elements are

ordered.

The function back is not to be used to return the last element because

the pointer last is set to NULL.

6. Ordered Linked Lists: search()

Algorithm

The function search is similar to the search function for general lists.

Here because the list is sorted, we can improve the search

algorithm.

1. Compare the search item with the current node in the list. If

the info of the current node is greater than or equal to the

search item, stop the search; otherwise, make the next node

the current node.

2. Repeat step 1 until either an item in the list is greater than or

equal to the search item is found, or no more data is left in the

list to compare with the search item.

6. Ordered Linked Lists: search()

template<class Type>bool orderedLinkedListType<Type>::search(const Type& searchItem){

bool found;nodeType<Type> *current;found = false;current = first;while(current != NULL && !found)

if(current->info >=searchItem) found = true;else current = current->link;

if(found) found = (current->info == searchItem);return found;

6. Ordered Linked Lists: insertNode()

Case 1: The list is initially empty: insert the new item at the

beginning and increment count by 1.

Case 2: The list is not empty and the new item is smaller than the

smallest in the list: insert the new item at the beginning and

increment count by 1.

Case 3: The list is not empty and the new item is larger than the

first item.

Case 3a: The new item is larger than the last item. Insert the new

item at the end of the list and increment count by 1.

Case 3b: The new item is to be inserted somewhere in the middle.

6. Ordered Linked Lists: insertNode()

Program

6. Ordered Linked Lists: deleteNode()

Case 1: The list is initially empty. We have an error.

Case 2: The item to be deleted is contained in the first node of the

list. We must adjust the head pointer of the list – first .

Case 3: The item to be deleted is somewhere in the list. In this

case, current points to the node containing the item to be deleted,

and trailCurrent points to the node just before the node pointed to

by current.

Case 4: The list is not empty, but the item to be deleted is not in

the list.

After deleting the node, count is decremented by 1.

6. Ordered Linked Lists: deleteNode()

Program

7. Doubly Linked Lists

A doubly linked list is a linked list in which every node has a next

pointer and a back pointer.

15 20 39

7. Doubly Linked Lists: Class Part I

template<class Type>struct nodeType{

Type info;nodeType<Type> *next;nodeType<Type> *back;

template<class Type>class doublyLinkedList{

friend ostream& operator<< (ostream&, const doublyLinkedList<Type>&);public:

const doublyLinkedList<Type>& operator=(const doublyLinkedList<Type>&);void initializeList();bool isEmptyList();void destroy();void reversePrint();int length();

7. Doubly Linked Lists: Class Part II

Type front();

Type back();

bool search(const Type& searchItem);

void insertNode(const Type& insertItem);

void deleteNode(const Type& deleteItem);

doublyLinkedList();

doublyLinkedList(const doublyLinkedList<Type>& otherList);

protected:

int count;

nodeType<Type> *first;

nodeType<Type> *last;

private:

void copyList(const doublyLinkedList<Type>& otherList);

7. Doubly Linked Lists: Default constructor and isEmptyList

template<class Type>doublyLinkedList<Type>::doublyLinkedList(){

first = NULL;last = NULL;count = 0;

doublyLlinkedList<Type>::isEmtyList()

return(first == NULL);

7. Doubly Linked Lists: destroy

void doublyLinkedList<Type>::destroy()

nodeType<Type> *temp;

while(first != NULL)

temp = first;

first = first->next;

delete temp;

last = NULL;

count = 0;

7. Doubly Linked Lists: initializeList and length

void doublyLinkedList<Type>::initializeList()

destroyList();

int doublyLinkedList<Type>::length()

return count;

7. Doubly Linked Lists: operator<<

ostream& operator<<(ostream& osObject, const doublyLinkedList<Type>& list)

nodeType<Type> *current; // pointer to traverse the list

current = list.first;

current = current->next;

return osObject;

7. Doubly Linked Lists: reversePrint

void doublyLinkedList<Type>::reversePrint()

nodeType<Type> *current;

current = last;

current = current->back;

7. Doubly Linked Lists: search

template<class Type>void doublyLinkedList<Type>::search(const Type& searchItem){

bool found = false;nodeType<Type> *current;current = first;while(current != NULL && !found)

if(current->info >= searchItem) found true;else

current = current->next;if (found) found = (current->info == searchItem);return found;

7. Doubly Linked Lists: front and back

void doublyLinkedList<Type>::front()

assert(first != NULL);

return first->info;

void doublyLinkedList<Type>::back()

assert(first != NULL);

return last->info;

7. Doubly Linked Lists: insertNode

Program

7. Doubly Linked Lists: deleteNode

Program

Insertion and deletion of items from a linked list includes special

cases: insertion/deletion at the beginning or in an empty list.

Hint: never insert before the first item or after the last item and

never delete the first node.

In the case of an ordered list, set up two virtual nodes header at

the beginning and trailer at the end.

Afirst zzzzzzzz

A Ahmad Ali Marwafirst zzzzzzzz

The usual operations on a linked list with header and trailer nodes are:

Exercise1.Write the definition of the class that defines a linked list

with header and trailer nodes as an ADT.

2.Write the definitions of the member functions of the

class defined in 1 (you may assume that the elements of

the linked list with header and trailer nodes are sorted in

an ascending order).

3.Write a program to test various operations of the class

defined in 1.

Exercise1.Write the definition of the class that defines a linked list

with header and trailer nodes as an ADT.

class defined in 1 (you may assume that the elements of

the linked list with header and trailer nodes are sorted in

an ascending order).

defined in 1.

A circular linked list is a linked list in which the last node points to the first node.

first 34

34 20 15 -12

The usual operations on a circular linked list are:

Exercise1.Write the definition of the class that defines a sorted

circular linked list as an ADT.

class defined in 1 (you may assume that the elements

are sorted in an ascending order).

defined in 1.

Chapter 5 Linked Lists Dr. Youssef Harrath yharrath@uob.edu.bh.

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