Organization of data and the Organization of data and the relationship among its members relationship among its members is called as data structureis called as data structure

Data Structure

Why we need Linked List?What are the problems with Arrays?Size is fixedArray Items are stored contiguouslyInsertions and deletion at particular position is complexWhy Linked list ? Size is not fixed Data can be stored at any place Insertions and deletions are simple and faster

What are Linked ListsWhat are Linked Lists

A linked list is a linear data structure.

Nodes make up linked lists.Nodes are structures made

up of data and a pointer to another node.

Usually the pointer is called next.

A linked list consists of:◦ A sequence of nodes

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a b c d

Each node contains a value

and a link (pointer or reference) to some other node

The last node contains a null link

The list may (or may not) have a header

myList

Linked List Types Singly Linked list Doubly linked lists Circular singly linked list Circular doubly linked lists

Each node has only one link part

Each link part contains the address of the next node in the list

Link part of the last node contains NULL value which signifies the end of the node

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200015 NULL20

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Singly Linked ListEach node points the next node . It is

a one way list.First

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Circular Singly Linked ListLast node contains the address of the first node

First

Doubly Linked listContains the address of previous node

and next node

NULL

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First

Circular Doubly Linked listContains the address of first node and

last node

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Operations on Linked ListCreation of the linked listInsertion of nodesTraversal of the linked listSearch a specific node in the linked listDeletion of a node in the linked list

Creation of the linked listCreation of a LL is a special case of insertion, i.e. insertion

into an empty list.If the value of start is null, it implies that there are no nodes in the list.Creation is a two step processa)Creating the new node

b)Storing the address of the new node in the start

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Next

Creation of the Linked ListStart

Info Next

There are three ways to insert a node into the list.

Insertion at the beginning Insertion at the end Insertion after a particular node

There are two steps to be followed:-

a)Make the next pointer of the node point towards the first node of the list

b)Make the start pointer point towards this new node

If the list is empty simply make the start pointer point towards the new node;

Algorithm to Insert an Element from the front INSERT(Start,data)1.Allocate memory to New2. Set NewInfo=data3.NewNext=start4.Start=New5.Return Start

Here we simply need to make the next pointer of the last node point to the new node

Here we again need to do 2 steps :-

Make the next pointer of the node to be inserted point to the next node of the node after which you want to insert the node

Make the next pointer of the node after which the node is to be inserted, point to the node to be inserted

Traversal of a LL means to traverse each node of the list, and visiting each node exactly once.Algorithm:1.Set Ptr to Start.2.Repeat steps 3 and 4 until Ptr is not equal to Null.3.Print the Info part of each node to which Ptr is pointing currently.4.Advance the pointer Ptr so that it points to the next node.5.End

a b c d

start Info

NextPtr

Logic using CTraverse(){Struct node *ptr;Ptr=start;While(ptr){Print(“The current node %s”, ptritem-no);Ptr=ptrnext;}}

Searching involves finding the required element in the list

We can use various techniques of searching like linear search or binary search where binary search is more efficient in case of Arrays

But in case of linked list since random access is not available it would become complex to do binary search in it

We can perform simple linear search traversal

Algorithm1. Set Ptr to start2. Input the item to be searched3. While Ptr!=null do steps 4 and 54. Compare the item with the given value. If

they are same ,exit from the loop and goto step 6, else

5. Set Ptr to next node6. Report that the data found in the

list .Otherwise it doesn’t exist .

In linear search each node is traversed till the data in

the node matches with the required value

void search(int x){ node*temp=start; while(temp!=NULL) { if(temp->data==x) { Print “FOUND ”; break; } temp=temp->next; }}

Deletion of a node is carried out in two steps viz,a)Logical deletion pointer shuffling in order to

remove the linksb)Physical deletion release the memory

occupied using free() functionHere also we have three cases:- Deleting the first node Deleting the last node Deleting the intermediate node

Here we apply 3 steps:- Making the start pointer point towards the 2nd node Free the space associated with first node Operating system collects the free space of the

memory and use it with available free space.The process is given by Temp=start; Start=startnext; Free(temp)

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start

Here we apply 2 steps:-

Traverse the list to find the last node. Deleting the last node via delete keyword

node3 node2 node1

start

Traverse the list to find the node to be deleted.

Search is used for this purpose. Refer that as curr_ptr. Then delete that node by setting the pointers as

Prevnext=curr_ptrnext; Then physical deletion is achieved by free().

node1 node2 node3

To be deleted

The node in DLL may be deleted At the beginning At the end At any desired positionSteps to be followed1. If the list is empty display underflow message2. If a single node exists, set both the pointers as Null. Else if it is the

first node, then delete it and update the pointers.3. Else if, it is the last node, then delete it and update the right

pointer.4. Restore the deleted node to the free list

Generalized list A is a finite sequence of n>=0 elements. A=(α0 ….. α n-1 ), here A name of the list and α0 ….. α n-1

represents the elements. It is either atom or a list. Name is given by capital letter and elements by small case.Ex:1. D=() the null (or) empty list and its length is zero2. A=(a(b,c)) a list of length 23. B=(A,A,()) a list of length 3, the third one is null.4. C=(a,c) a recursive list of length 2, c corresponds to the

infinite list.

Linked stack In linked stack we can easily add a node at

the top or delete a node from the top. It is similar to push and pop the elements. A stack can be accessed only through its

top element,and a linked list can be accessed by using the pointer to its first element.

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Top

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Linked Stack

Linked list representations of queue are easy to handle.

We need two pointers namely Front and Rear.

Front represents the beginning of the queue and rear represents the end of the queue.

Q.Rear=null indicates the queue is empty.

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Front

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Rear

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Linked Queue

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Header Linked List

Header Node

The header for a LL is a pointer variable that locates the beginning of the list

HLL is a LL which always contains a special node called the header node.

Header node is at the beginning of the list. Dummy nodes placed as the first node of a list

which is used to simplify linked list processing. It may or may not contain meaningful

information. It does not represents an item in the list. The info portion of the such a header node

might be unused. It is used to keep the global information about

the entire list.