Linked lists

Prof. B. Majhi, HOD Dept, CSE NIT, Rourkela1

Linked List

Why Linked List• Arrays are fixed-length• To expand them, you create a

new, longer array, and copy the contents of the old array into the new array

• Also problem is there to insert or delete an element from an array

Continue…….• Solution: Attach a pointer to

each item in the array, which points to the next item–This is a linked list–An data item plus its pointer is called a node

Definition of linked listA linked list, or one-way list, is a linear collection of data elements,called nodes, where the linear order is given by means of pointer.

Node representation in a Linked List

infoLinkstruct node

data_type info;

struct node *link;

struct node *ptr;

Diagram Of Linked List

infostart info info NULL

Dynamic Memory Allocation• How can we allocate memory at run-time

instead of compile time?

• ANSI C provides standard functions that helps to allocate memory at run time.

• <alloc.h> is the required header file which must be on your include path to use the standard functions for dynamic memory allocation.

#include <alloc.h >This header file has the following routines used for dynamic memory allocation

•malloc()•calloc()•realloc()•free()

malloc()• malloc() allocates a block of Size bytes

from the memory heap.• malloc() does not assign any value to the

allocated memory space so by default it contains garbage value

• It allows a programmer to allocate memory explicitly as it's needed, and in the exact amounts needed.void *malloc (unsigned long Size);

Static Allocation:{ int a = 10;int *p;p = &a;printf(“%d”, p); printf(“%d”, *p); printf(“%d”, &a); printf(“%d” &p); }

=>2000

Dynamic Allocation with malloc:

{int *p;p = (int *) malloc (sizeof (int));scanf(“%d”, p); printf(“%d”, *p); printf(“%d” &p);}

calloc()• Allocates a memory block for a given

number and size of items• calloc() assign zero value to the

allocated memory space so by default it contains zero

void *calloc (unsigned short NoOfItems, unsigned short SizeOfItems);

Dynamic Allocation with calloc:{int n,i,*p, sum=0;printf(“Enter the size of array:”);scanf(“%d”,n);p = (int *) calloc (n,sizeof (int));for(i=0; i<n; i++)scanf(“%d”, (p+i));

Continuing…

for(i=0; i<n; i++){sum + = *(p+i); printf(“%d Element of array is :”,i,*(p+i) );}

printf(“Sum of elements in the array: %d” , sum);}

realloc()• Reallocates allocated memory.

• realloc() attempts to shrink or expand the previously allocated block to NewSize bytes.

void *realloc (void *Ptr, unsigned longNewSize);

Dynamic Allocation with realloc:

{char *ptr;int n;printf("\nEnter the size of the string");scanf("%d",&n);ptr=(char *) calloc(n,sizeof(char));printf("\n Enter the string");scanf("%s",ptr);

Continuing…

printf("\n Enter the size of new string");scanf("%d",&n);ptr=(char *)realloc(ptr,n);printf("\n Enter the string");scanf("%s",ptr);printf("\n%s",ptr);}

Assignments: dynamic memory allocation

1. Merging of two arrays 2. Find the followings

a) Sum of elements in an arrayb) Max and min elements in an arrayc) Reverse the elements in an array

free()• Frees an allocated block.• free deallocates a memory block allocated

by a previous call by malloc or calloc.

free(p);This pointer may be any type of pointer

variable.

Creation of LIFO Linked List

Rollstart NameRoll Name Roll Name Roll Name Null

Program:#include<alloc.h>#include<stdio.h>#include<conio.h>// Node declarationtypedef struct node{int roll_no;char name[50];struct node *next;}student;

Continuing…int main(){student *start,*ptr;char ch;start = (student *) malloc (sizeof(student));ptr=start;printf("\n Enter roll no of the student:::");scanf("%d",&start->roll_no);

continuing…printf("\n Enter name of the student:::");

scanf("%s",start->name);

printf("\n Enter your choice U want to continue or not:::");

scanf("%c",&ch);

continuing…while(ch=='Y'||ch=='y') {ptr->next=(student *) malloc (sizeof(student *));

ptr=ptr->next;printf("\n Enter roll no of the student:::");scanf("%d",&ptr->roll_no);printf("\n Enter name of the student:::");scanf("%s",ptr->name);printf("\n Enter your choice. U want to

continue or not");scanf("%c",&ch); }

continuing…ptr->next=NULL;printf("\n Informations of the students are:");

ptr=start;while(ptr!=NULL){printf("\n Roll no of the student=%d and name =%s",ptr->roll_no, ptr->name);ptr=ptr->next;} }

Types of Linked List• Single Linked List• Circular Linked List• Doubly Linked List

Operations on Linked List• Traversing a List• Insertion of a node into a List• Deletion of a node from a List• Copy a linked list to make a

duplicate• Merging two linked list into a larger

list• Searching for an element in a list

Insertion of a node into a List

• Insert at front (as a first element)

• Insert at end (as a last element)

• Insert at any position.

Insert at front

datastart data data NULL

datanew

Procedure InsertFirst()1.New = Getnode() 2. If(New = NULL) thena. Print “insufficient memory: No insertion”b. Exit

3. Elsea. New.info=datab. New.link=startc. start = New

4. Endif5. Stop

Procedure Getnode(){

struct node

struct node *link;

struct node *ptr = (struct node *) malloc(sizeof(structnode));

return (ptr); }

Insert at end

data data data NULL

datanew NULL

Procedure InsertEnd()1.New = Getnode(Node)2. If(New = NULL) thena. Print “Memory underflow: No insertion”b. Exit

3. Elsea. ptr = start

b. While(ptr.link != NULL) doi. ptr =ptr.link

c. End Whiled. ptr.link=Newe. New.info = dataf. New.link = NULL

4. Endif5. Stop

Insert at any position

data data datastart NULL

datanew

ProcedureInsertIntermediate()1.New = Getnode(Node) 2. If(New = NULL) thena. Print “Memory underflow: No insertion”b. Exit

3. Elsea. ptr = startb. While(ptr.data != key) and (ptr.link != NULL)do

i. ptr =ptr.linkc. End While

d. if(ptr.link=NULL) theni. Print ”Key is not available in the list”ii. Exit

f. Elsei. New.info = dataii. New.link = ptr.linkiii. ptr.link = New

g. Endif4. Endif5. Stop

Deletion of a node from a List

• Delete the first element• Delete the last element• Delete any intermediate

element.

Delete the first element

datastart data data NULL

ProcedureDeleteFirst()1. ptr = start 2. If(ptr.link = NULL) thena. Print “The List is empty: No deletion possible”b. Exit

3. Elsea. ptr=ptr.linkb. start.link=NULLc. start = ptr

4. Endif5. Stop

Delete the end element

info info info NULLNULLstart

ProcedureDeleteEnd()1. ptr = start 2. If(ptr.link = NULL) thena. Print “The List is empty: No deletion

possible”b. Exit

3. Elsea. While(ptr.link != NULL) do

i. ptr1 = ptrii. ptr =ptr.link

b. End Whilec. ptr1.link=NULL4. Endif5. Stop

Delete any intermediate element

infostart info info NULL

ProcedureDeleteIntermediate()1. ptr = start 2. While(ptr.data != key) and (ptr.link !=

NULL)doi. ptr1=ptrii. ptr =ptr.link

3. End While

4. if(ptr.link=Key) thenptr1.link = ptr.link

5. ElsePrint “Node don’t exist : Deletion is unsuccessful”

6. Endif5. Stop

Assignments on Linked List1. Traversing a List2. Insertion of a node into a List3. Deletion of a node from a List4. Copy a linked list to make a

duplicate5. Merging two linked list into a

larger list6. Searching for an element in a list

Applications of Linked Lists

1. Polynomial Representation and operation on PolynomialsEx: 10 X 6 +20 X 3 + 55

2. Sparse Matrix Representation0 0 1122 0 00 0 66

Helpful to save space when large sparse matrices are stored

3. Queue, Stack implementation

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