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Program to reverse a linked list



/* Program to reverse a linked list */

#include <stdio.h>
#include <conio.h>
#include <alloc.h>

/* structure containing a data part and link part */
struct node
{
int data ;
struct node *link ;
} ;

void addatbeg ( struct node **, int ) ;
void reverse ( struct node ** ) ;
void display ( struct node * ) ;
int count ( struct node * ) ;

void main( )
{
struct node *p ;
p = NULL ; /* empty linked list */

addatbeg ( &p, 7 ) ;
addatbeg ( &p, 43 ) ;
addatbeg ( &p, 17 ) ;
addatbeg ( &p, 3 ) ;
addatbeg ( &p, 23 ) ;
addatbeg ( &p, 5 ) ;

clrscr( ) ;
display ( p ) ;
printf ( "\nNo. of elements in the linked list = %d", count ( p ) ) ;

reverse ( &p ) ;
display ( p ) ;
printf ( "\nNo. of elements in the linked list = %d", count ( p ) ) ;
}

/* adds a new node at the beginning of the linked list */
void addatbeg ( struct node **q, int num )
{
struct node *temp ;

/* add new node */
temp = malloc ( sizeof ( struct node ) ) ;
temp -> data = num ;
temp -> link = *q ;
*q = temp ;
}

void reverse ( struct node **x )
{
struct node *q, *r, *s ;

q = *x ;
r = NULL ;

/* traverse the entire linked list */
while ( q != NULL )
{
s = r ;
r = q ;
q = q -> link ;
r -> link = s ;
}

*x = r ;
}

/* displays the contents of the linked list */
void display ( struct node *q )
{
printf ( "\n" ) ;

/* traverse the entire linked list */
while ( q != NULL )
{
printf ( "%d ", q -> data ) ;
q = q -> link ;
}
}

/* counts the number of nodes present in the linked list */
int count ( struct node * q )
{
int c = 0 ;

/* traverse the entire linked list */
while ( q != NULL )
{
q = q -> link ;
c++ ;
}
return c ;
}



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