Linked Lists Objects->Connected->by->Pointers. What is a Linked List? List: a collection Linked: any...

Linked ListsObjects->Connected->by->Pointers

What is a Linked List?List: a collectionLinked: any individual item points

to another item to connect themLinked List:

◦A collection of objects (data + functions)

◦Data includes items of the same data type(s)

◦A way of implementing a container class

List OperationsCreate itself (initialize)Insert an itemDelete an itemPrint itselfKnow the number of items it

contains

Linked List Container ClassImplementation of the container

class is based on the concept of a node

Node: holds two important components◦The item that the user wants (private

data and public functions)◦A pointer to the next node in the list

(next)

Anatomy of a Node

Pointer to the head of the list

Tux Penquin data

Pointer to next node

Node

Null pointerAt the end of the list

How to Code a Node

class node{ public:

typedef double value_type;…

private:value_type penquin;node *next;

};

What Else Does a Node Need?Data is private Accessor MethodMutator Method

From a Node to a ListCreate a pointer to a node object

◦Remember the pointer to a dynamic array? Create an add function to add a new

node and link it to a list (and other useful functions)◦Textbook creates these functions as non-

member functions in the linked list toolkit◦You can also create another class to hold all

of these useful functions Bonus: node is more easily accessible if it is a

member of the same class as the functions that manipulate it!

From a Node to a ListNon-Member functions in a Linked List Toolkit

Begin with a “head” pointer to a node

This pointer must be declared in mainmain {

node *head;}

From a Node to a ListMember Functions in a Linked List Class

Begin with a pointer to a node This pointer must be declared in the

private section of your linked list class:

class myList { … private: node *head;};

Class Functions versus Non-Member Functions

main

{

node *head;

}

class myList { … private: node *head;

};

From a Node to a List: How To Initialize a Node to Add to a ListSo far, we have a pointer for a node object,

but where does it point?Remember how to make a dynamic array grow?Create a function to add nodes to the list

◦1. Declare a node object◦2. Use the new operator to initialize it in the

heap◦3. Initialize the data to a valid state (put some

data in it)◦4. Get the original “head” pointer to point to it

Which end of the list do we add a new node?

From a Node to a List: Where To Add a NodeThe first node should be at the

head of the listWhere should the second node

go?◦Head of the list◦Tail of the list

How do we know where the head of the list is? Do we know where the tail is?

From a Node to a List: The Add Function◦ 1. Declare a node

object◦ 2. Use the new

operator to initialize it in the heap

Node *newOne = new Node;

From a Node to a List: Member Add Function versus Non-Member Add FunctionNode * myList::AddNode(value_type myData)

{


…

}

void AddNode(node*& head, value_type myData)

{


…

}

From a Node to a List: 1. Declare a node

object2. Use the new


3. Initialize the data to a valid state (put some data in it)

4. Get the original “head” pointer to point to it

newOne->set_data(“Joe”);


{

Node newOne = new Node;


return newOne;

}


{



head = newOne;

}


From a Node to a List: What about Joe’s Next pointer?

Joe

newOne

head_ptr

From a Node to a List: Adding to the Head of a List that Isn’t Empty


head_ptr

newOne

From a Node to a List: One MORE Thing…

◦1. Declare a node object◦2. Use the new operator to initialize

it in the heap◦3. Initialize the data to a valid state

(put some data in it)◦3b. Set the node’s next pointer to

point to the head of the list◦4. Get the original “head” pointer to

point to it

From a Node to a List: 1. Declare a node

object2. Use the new


3. Initialize the data to a valid state (put some data in it)

3b. Set the node’s next pointer to point to the head of the list


newOne->set_next(head);


{




return newOne;

}


{




head = newOne;

}

3a. Set the node’s next pointer to point to the head of the list

From a Node to a List: Adding to the Head of a List that Isn’t Empty


head_ptr

newOne

From a Node to a List: Does it Work for an Empty List?What will the new node’s next

pointer point to if the list is empty?


Joe

newOne

head_ptr???

What if you initialize head_ptr as NULL?

Removing a Node From a ListNodes often need to be removed

from a linked listFrom front of the listFrom another location in the list

◦Two operations are needed Search for node to remove Remove node

Removing the node at the head of a list


head_ptr

Is this OK?delete head_ptr;



head_ptr

doomedWhat if I create a new pointer and point it to the head of the list …



head_ptr

doomed

…and then point the head pointer to the next node…



head_ptr

Can I delete doomed now?

doomed

Member Function Code

Node *doomed = list;list = list->get_next();delete doomed;

Does This Work For Removing ANY Node?This method works because we

know where the head node isWhat of the node is in the middle

or the end? Do we know where it is?◦Our find function can locate the node◦But what about all of the nodes in

front of that node?

Does This Work For Removing ANY Node?


head_ptr

doomed

Does this work? And what about the penguin in the green hat?

???



head_ptr

previous

What if I remember where the previous node is…and then I redirect that nodes’ next pointer instead?



head_ptr

previous …but what if I

need to delete the last node?


Redirect Which Pointer?

Redirect Where?

Deleting 1st Node Head pointer to point to

Head pointer’s->next

Deleting Middle Node

Previous pointer to point to

Previous pointer’s -> next

Deleting Last Node Previous pointer to point to

NULL

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