Linked List Action

8/13/2019 Linked List Action

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Chapter 5 introduces the often-

used data structure of linked lists.

This presentation shows how toimplement the most common

operations on linked lists.

Linked Lists in Action

CHAPTER 5Data Structures and Other Objects


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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;

};

Declarations for Linked Lists


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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


node *link_field;

};



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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


node *link_field;

};



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A program can keep track of the front

node by using a pointer variable such

as head_ptrin 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


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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

nullin the head pointer.

head_ptr

null


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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, 13,

to the frontof the linked listshown here.

10

15

7

null

head_ptr

entry

13


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Create a new node, pointed to

by a local variable insert_ptr.

10

15

7

null

head_ptr

entry

13

insert_ptr



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insert_ptr = new node;

10

15

7

null

head_ptrentry

13

insert_ptr



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10

15

7

null

head_ptrentry

13

insert_ptr13

insert_ptr = new node;

Place the data in the new node's

data_field.



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10

15

7

null

head_ptrentry

13

insert_ptr13

insert_ptr = new node(entry, head_ptr);

The correct new node

can be completely

created in one step by

calling an appropriatenode constructor.



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10

15

7

null

head_ptrentry

13

insert_ptr13


Make the old head pointer

point to the new node.



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10

15

7

null

head_ptrentry

13

insert_ptr13


head_ptr = insert_ptr;



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10

15

7

null

head_ptr

13

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

front.



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

{

node *insert_ptr;



}



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{

node *insert_ptr;



}Does the function work

correctly for the empty

list ?


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head_ptrentry

13 null


Does the function work

correctly for the empty

list ?


{

node *insert_ptr;



}


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head_ptrentry

13 null

insert_ptr13


{

node *insert_ptr;



}

null


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head_ptr

13

null


{

node *insert_ptr;



}When the function

returns, the linked list

has one node.


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Caution!

Always make sure that

your linked list

functions work

correctly with an

empty list.

EMPTY LIST


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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. . .


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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);


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A pointer

to the

head of

the list


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Otherwise (if the new node will not be first):

Start by setting a pointer named previous_ptrto point to thenode which is just beforethe new node's position.


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15

10

7

null

head_ptr


Start by setting a pointer named previous_ptrto point to thenode which is just beforethe new node's position.

In this example, the

new node will be

the second node

previous_ptr


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15

10

7

null

head_ptr


Start by setting a pointer named previous_ptrto point to thenode which is just before the new node's position

What is the name of

this orange pointer ?

Look at the pointer

which is in the node

*previous_ptr

previous_ptr


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15

10

7

null

head_ptr



This pointer is called

previous_ptr->link_field

(although this name may

be private to the node)

What is the name of

this orange pointer ?

previous_ptr


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15

10

7

null

head_ptr



previous_ptr->link_field

points to the head

of a small linked

list, with 10 and 7

previous_ptr


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15

10

7

null

head_ptr


Start by setting a pointer named previous_ptrto point to thenode which is just before the new node's position.

The new node must

be inserted at the

front of this small

linked list.

13

Write one C++ statement

which will do the insertion.

previous_ptr


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15

10

7

null

head_ptr



13

What might cause this

statement to fail to compile?

previous_ptrlist_head_insert(previous_ptr->link_field, entry);


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15

10

7

null

head_ptr



13

Use a node member function

to get the link field if

needed.

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


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Set a pointer namedprevious_ptrto point to the node

which is just before the new node's position.

Make the function call:list_head_insert(previous_ptr->link( ), entry);


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The process of adding a new node in the middle

of a list can also be incorporated as a separate

function. This function is called list_insert in the

linked list toolkit of Section 5.2.


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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.

Well look at the pseudocode for removing a node

from the front of a linked list.


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Removing the Head Node

10 15 7

nullhead_ptr

13

Start by setting up a temporary pointer named remove_ptrto

the head node.

remove_ptr


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10 15 7

null

head_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.


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10 15 7

nullhead_ptr

13

Set up remove_ptr.


remove_ptr


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Set up remove_ptr.


delete remove_ptr; // Return the node's memory to heap.

10 15 7

nullhead_ptr

13

remove_ptr


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Heres what the linked list looks like after the removal finishes.

10 15 7

nullhead_ptr


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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


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THE END

Presentation copyright 2010, Addison Wesley Longman,

For use withData Structures and Other Objects Using C++

by Michael Main and Walter Savitch.

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Students and instructors who useData Structures and Other Objects Using C++are welcome

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intact.

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