linked list 1. introduction to linked list 2. node class 3. linked list 4. the bag class with linked...

Linked List

1.1. Introduction to Linked ListIntroduction to Linked List

2.2. Node ClassNode Class

3.3. Linked ListLinked List

4.4. The Bag Class with Linked ListThe Bag Class with Linked List

Linked List

Linked ListLinked List Is a series of connected nodes, where each Is a series of connected nodes, where each

node is a data structure with data field and node is a data structure with data field and pointer(s) field.pointer(s) field.

Advantages over array implementationAdvantages over array implementation Can grow and shrink in size, with no upper limitCan grow and shrink in size, with no upper limit Fast insertion and deletionFast insertion and deletion

Ωhead

For this presentation, nodes in a linked list are objects, as shown

here.

data_field

link_field

10

data_field

link_field

15

data_field

link_field

7

null

class node{public: typedef double value_type; ...private value_type data_field; node *link_field;};

DeclarationsDeclarations forfor LinkedLinked ListsLists

typedef Keyword

typedef int age_t;typedef int age_t;typedef int count_t;typedef int count_t;typedef double gpa_t;typedef double gpa_t;……age_t myAge = 21;age_t myAge = 21;count_t numElements = 5;count_t numElements = 5;gpa_t myGPA = 3.8;gpa_t myGPA = 3.8;

void someFunc(age_t age, count_t count);void someFunc(age_t age, count_t count);

is clearer than is clearer than

void someFunct(int age, int count);void someFunct(int age, int count);

Why Use typedef?

Using typedefs can make your code clearer

Using ypedefs can make your code easier to modify

The data_field of each node is a type called value_type, defined by a typedef.

data_field

link_field

10

data_field

link_field

15

data_field

link_field

7

null

class node{public: typedef int value_type; ...private value_type data_field; node *link_field;};


Each node also contains a link_field which is a pointer to another node.

data_field

link_field

10

data_field

link_field

15

data_field

link_field

7

null

class node{public: typedef int value_type; ...private value_type data_field; node *link_field;};


Your Turn

Write the public interface for the Node Write the public interface for the Node class—e.g, Constructors, accessors, class—e.g, Constructors, accessors, modifiers.modifiers.

Solution

class node{public: //CONSTRUCTORS node(); node(const valueType& value, node* ptr); //CONSTANT FUNCTIONS valueType getData(); node* getNext(); //MODIFIER FUNCTIONS void setData(valueType newData); void setLink(node* newLink);

private: valueType data; node* next;};

Declarations for Linked Lists

A program can keep track of the front node by using a pointer variable such as head_ptr in this example.

Notice that head_ptr is not a node -- it is a pointer to a node.

head_ptr

data_field

link_field

10

data_field

link_field

15

data_field

link_field

7

null

Declarations for Linked Lists

A program can keep track of the front node by using a pointer variable such as head_ptr.

Notice that head_ptr is not a node -- it is a pointer to a node.

We represent the empty list by storing null in the head pointer.

head_ptr null

void list_head_insert(node*& head_ptr, const node::value_type& entry);

Inserting a Node at the Front

We want to add a new entry, We want to add a new entry, 13, to the 13, to the frontfront of the linked of the linked list shown here.list shown here.

10

15

7

nullhead_ptr

entry

13


Create a new node, pointed to by a local variable insert_ptr.

10

15

77

nullhead_ptrentry

13

insert_ptr



insert_ptr = new node;

10

15

7

nullhead_ptr

entry

13

insert_ptr



10

15

7

nullhead_ptr

entry

13

insert_ptr13


Place the data in the new node's data_field.



10

15

7

nullhead_ptr

entry

13

insert_ptr

13


Place the data in the new node's data_field.

Connect the new node to the front of the list.



10

15

7

nullhead_ptr

entry

13

insert_ptr13

insert_ptr = new node(entry, head_ptr);

The correct new node can be The correct new node can be completely created in one completely created in one step by calling an appropriate step by calling an appropriate node constructor.node constructor.



10

15

7

nullhead_ptr

entry

13

insert_ptr

13

insert_ptr = new node(entry, head_ptr);Make the old head pointer point to the new node.



10

15

7

nullhead_ptr

entry

13

insert_ptr

13

insert_ptr = new node(entry, head_ptr);head_ptr = insert_ptr;




head_ptr = insert_ptr;

10

15

7

nullhead_ptr

13

When the function returns, thelinked list has a new node at thefront.


void list_head_insert(node*& head_ptr, const node::value_type& entry){ node *insert_ptr;



}






} Does the function work

correctly for the empty list ?

head_ptrentry

13 null


Does the function work

correctly for the empty list ?




}


head_ptrentry

13 null

insert_ptr

13




}

null


head_ptrentry

13

insert_ptr

13

null




}


head_ptr

13

null




}When the function

returns, the linked list has one node.

Caution!

Always make sure that your linked list functions work correctly with an empty list.

Pseudocode for Inserting Nodes

Nodes are often inserted at places other than the front of a linked list.

There is a general pseudocode that you can follow for any insertion function. . .


Determine whether the new node will be the first node in the linked list. If so, then there is only one step:

list_head_insert(head_ptr, entry);


Determine whether the new node will be the first node Determine whether the new node will be the first node in the linked list. If so, then there is only one step:in the linked list. If so, then there is only one step:

The

func

tion

we

alre

ady

wro

te





A pointerto the

head ofthe list




The data to put

in the new node


Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the

node which is just before the new node's position.


15

10

7

nullhead_ptr



In this example, thenew node will bethe second node

previous_ptr


15

10

7

nullhead_ptr


node which is just before the new node's position

What is the name of this orange pointer ?

Look at the pointerwhich is in the node

*previous_ptr

previous_ptr


15

10

7

nullhead_ptr



This pointer is calledprevious_ptr->link_field(although this name maybe private to the node)

What is the name of What is the name of this orange pointer ?this orange pointer ?

previous_ptr


15

10

7

nullhead_ptr



previous_ptr->link_fieldpoints to the headof a small linkedlist, with 10 and 7

previous_ptr


15

10

7

nullhead_ptr



The new node mustbe inserted at thefront of this small

linked list.

13

Write one C++ statement which will do the insertion.

previous_ptr


15

10

7

nullhead_ptr


node which is just before the new node's position.13

What might cause this statement to fail to compile?

previous_ptr

list_head_insert(previous_ptr->link_field, entry);


15

10

7

nullhead_ptr


node which is just before the new node's position.13

Use a node member function to get the link field if needed.

previous_ptr

list_head_insert(previous_ptr->link( ), entry);




Otherwise (if the new node will not be first): Set a pointer named previous_ptr to point to the node

which is just before the new node's position. Make the function call:

list_head_insert(previous_ptr->link( ), entry);


The process of adding a new node in the The process of adding a new node in the middle of a list can also be incorporated as a middle of a list can also be incorporated as a separate function. This function is called separate function. This function is called list_insert in the linked list toolkit of Section list_insert in the linked list toolkit of Section 5.2.5.2.

Pseudocode for Removing Nodes

Nodes often need to be removed from a linked list.

As with insertion, there is a technique for removing a node from the front of a list, and a technique for removing a node from elsewhere.

We’ll look at the pseudocode for removing a node from the front of a linked list.

Removing the Head Node

10 15 7

nullhead_ptr

13

Start by setting up a temporary pointer named remove_ptr to the head node.

remove_ptr


10 15 7

nullhead_ptr

13

Set up remove_ptr. head_ptr = remove_ptr->link( );

remove_ptr

Draw the change that this statement will make to the linked list.


10 15 7

nullhead_ptr

13

Set up remove_ptr. head_ptr = remove_ptr->link( );

remove_ptr


Set up remove_ptr. head_ptr = remove_ptr->link( ); delete remove_ptr; // Return the node's memory to heap.

10 15 7

nullhead_ptr

13

remove_ptr


Here’s what the linked list looks like after the removal finishes.

10 15 7

nullhead_ptr

It is easy to insert a node at the front of a list. The linked list toolkit also provides a function

for inserting a new node elsewhere It is easy to remove a node at the front of a

list. The linked list toolkit also provides a function

for removing a node elsewhere--you should read about this function and the other functions of the toolkit.

Summary

Doubly Linked List

head Ω

class node{ . . .private: elementType data; node* next; node* previous;};

class list{ . . .private: node* head; int count;};

Ω

insertAtFront()

head ΩΩ

newPtr ΩΩ

head Ω

newPtrΩ

insertAtFront()

void list::insertAtFront(valueType item){ node* temp = new node(item, NULL, NULL); if (isEmpty()) head = temp; else { temp->setNext(head); head->setPrevious(temp); head = temp; } count++;}

removeFromFront()

head ΩΩ

head Ω

temp

ΩΩ

removeFromFront()

valueType list::removeFromFront(){ valueType result = NIL;

if (!isEmpty()) { result = head->getData();

node* temp = head; head->setPrevious(NULL); head = head->getNext(); delete temp; count--; } return result;}

insertAtBack()

head ΩΩ

newPtr ΩΩ

headΩ

newPtr Ω

temp

temp

insertAtBack()void list::insertAtBack(valueType item){ node* newPtr = new node(item, NULL, NULL);

// find the last node if (isEmpty()) head = newPtr; else { node* temp = head; while (temp->getNext() != NULL) { temp = temp->getNext(); } temp->setNext(newPtr); newPtr->setPrevious(temp); } count++;}

removeFromBack()

head ΩΩ

head Ω

temp

ΩΩ

removeFromBack()

valueType list::removeFromBack(){ valueType result = NIL;

if (!isEmpty()) { // find last node node* temp = head; while (temp->getNext() != NULL) { temp = temp->getNext(); } // remove last node temp->getPrevious()->setNext(NULL); delete temp; } return result;}

Tail Pointer (to the last node)

head Ω

class node{ . . .private: elementType data; node* next;};

class list{ . . .private: node* head; node* tail; int count;};

tail

linked list 1. introduction to linked list 2. node class 3. linked list 4. the bag class with linked...

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