Write a C Program to check linked list is Palindrome or not

By | 08.04.2017

Check linked list is Palindrome or not


Write a C Program to check linked list is Palindrome or not. Here’s simple Program to check linked list is Palindrome or not in C Programming Language.


What is Linked List ?


Linked list is a linear data structure that contains sequence of elements such that each element links to its next element in the sequence. Each link contains a connection to another link.

Following are the important terms to understand the concept of Linked List.

  • Link − Each link of a linked list can store a data called an element.
  • Next − Each link of a linked list contains a link to the next link called Next.

Each element in a linked list is called as “Node”. Each node consists of its own data and the address of the next node and forms a chain. Linked Lists are used to create trees and graphs.


Below is the source code for C Program to check linked list is Palindrome or not which is successfully compiled and run on Windows System to produce desired output as shown below :


SOURCE CODE : :


/* C Program to check linked list is Palindrome or not */

#include<stdio.h>
#include<stdlib.h>

struct node
{
        int info;
        struct node *link;
};

struct node *create_list(struct node *start);
void display(struct node *start);
struct node *addatbeg(struct node *start,int data);
struct node *addatend(struct node *start,int data);
int isIdentical(struct node *p1, struct node *p2);
int isPalindrome(struct node *start);
struct node *reverse(struct node *start);

int main()
{
        struct node *start=NULL;
        start=create_list(start);
        display(start);
        if( isPalindrome(start) )
                printf("\nList is a Palindrome\n");
        else
                printf("\nList is not a Palindrome\n");

        return 0;

}/*End of main()*/

int isPalindrome(struct node *start)
{
        struct node *slowP, *fastP, *prev_slowP, *start_second;
        int result;

        if(start==NULL || start->link==NULL) /*List empty or only one element*/
           return 1;
        prev_slowP = slowP = fastP = start;
        while(fastP->link!=NULL && fastP->link->link!=NULL)
        {
                prev_slowP = slowP;
                slowP=slowP->link;
                fastP=fastP->link->link;
        }
        start_second = slowP->link;
        if(fastP->link == NULL)  /*odd number of elements in the list*/
    {
                start_second = reverse(start_second);  /*reverse the second half*/
                prev_slowP->link = NULL;
                result = isIdentical(start, start_second);/*compare the first half and second half*/
                start_second = reverse(start_second);  /*reverse second half to get the original order*/
                prev_slowP->link = slowP; /*Join first half with the middle element*/
                slowP->link = start_second;/*Join middle element with the second half*/
    }
        else /*even number of elements in the list*/
        {
                start_second = reverse(start_second);  /*reverse the second half*/
                slowP->link = NULL; /*node pointed by slowP is the last node of first half*/
                result = isIdentical(start, start_second);  /*compare the first half and second half*/
                start_second = reverse(start_second);  /*reverse second half to get the original order*/
                slowP->link = start_second; /*Join first half and second half*/
        }
        return result;
}/*End of isPalindrome()*/

struct node *reverse(struct node *start)
{
        struct node *prev, *ptr, *next;
        prev=NULL;
        ptr=start;
        while(ptr!=NULL)
        {
                next=ptr->link;
                ptr->link=prev;
                prev=ptr;
                ptr=next;
        }
        start=prev;
        return start;
}/*End of reverse()*/

int isIdentical(struct node *p1, struct node *p2)
{
        while(1)
        {
                if((p1==NULL)&&(p2==NULL))
                        return 1;
                if((p1==NULL)||(p2==NULL))
                        return 0;
                if(p1->info!=p2->info)
                        return 0;
                p1 = p1->link;
                p2 = p2->link ;
        }
}/*End of Identical()*/

struct node *create_list(struct node *start)
{
        int i,n,data;
        printf("Enter the number of nodes : ");
        scanf("%d",&n);
        start=NULL;
        if(n==0)
                return start;

        printf("\nEnter the element to be inserted : ");
        scanf("%d",&data);
        start=addatbeg(start,data);

        for(i=2;i<=n;i++)
        {
                printf("\nEnter the element to be inserted : ");
                scanf("%d",&data);
                start=addatend(start,data);
        }
        return start;
}/*End of create_list()*/

void display(struct node *start)
{
        struct node *p;
        if(start==NULL)
        {
                printf("\nList is empty\n");
                return;
        }
        p=start;
        printf("\nList is :\n");
        while(p!=NULL)
        {
                printf("%d ",p->info);
                p=p->link;
        }
        printf("\n\n");
}/*End of display() */

struct node *addatbeg(struct node *start,int data)
{
        struct node *tmp;
        tmp=(struct node *)malloc(sizeof(struct node));
        tmp->info=data;
        tmp->link=start;
        start=tmp;
        return start;
}/*End of addatbeg()*/

struct node *addatend(struct node *start,int data)
{
        struct node *p,*tmp;
        tmp=(struct node *)malloc(sizeof(struct node));
        tmp->info=data;
        p=start;
        while(p->link!=NULL)
                p=p->link;
        p->link=tmp;
        tmp->link=NULL;
        return start;
}/*End of addatend()*/

OUTPUT : :


/* C Program to check linked list is Palindrome or not */

************** OUTPUT ****************

Enter the number of nodes : 6

Enter the element to be inserted : 2

Enter the element to be inserted : 4

Enter the element to be inserted : 5

Enter the element to be inserted : 5

Enter the element to be inserted : 4

Enter the element to be inserted : 2

List is :
2 4 5 5 4 2


List is a Palindrome

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