CareerCup

simple, just to traverse through the list and swap next, prev pointer for each item.

void reverse(NODE **head)
{
    NODE *c = NULL, *temp = NULL;
    if(*head == NULL)
         return;
    while(*head)
    {
         temp = (*head)->next;
         (*head)->next = c;
         (*head)->prev = temp;
         c = *head;
         *head = temp;
     }
     *head = c;
}

void reverse(node *head)
{
node *current,*temp;
temp = NULL;
current = head;
while(current)
{
current->prev = current->next;
current->next=temp;
temp = current;
current = current->prev;
}
*head = temp;
}

//Write a function for reversing a doubly linked list.

#include<stdio.h>

struct node *head;

struct node
{
int val;
struct node *next;
struct node *prev;
};

void insert(int x, struct node *head)
{
struct node *p;
struct node *t = (struct node*) malloc (sizeof(struct node));
t->val = x;
t->next = t->prev = NULL;

p = head;
while(p->next != NULL)
{
p = p->next;
}
t->prev = p;
p->next = t;
}

void reverse(struct node *head)
{
struct node *p,*temp;
p = head;
while(p != NULL)
{
temp = p->prev;
p->prev = p->next;
p->next = temp;
p = p->prev;
}
head = temp->prev;
printf("\nReversed Values in the linked list are :\n");
p = head;
while(p != NULL)
{
printf("%d\t",p->val);
p = p->next;
}
}

void display(struct node *head)
{
struct node *p;
p = head;
while(p != NULL)
{
printf("%d\t",p->val);
p = p->next;
}
}

int main()
{
head = (struct node*) malloc (sizeof(struct node));
head->next = head->prev = NULL;
head->val = 4;
insert(5,head);
insert(6,head);
insert(7,head);
printf("\nValues in the linked list are :\n");
display(head);
reverse(head);
}

#include<stdio.h>
#include<malloc.h>

struct node
{
int data;
struct node *prev;
struct node * next;
};

void append(struct node **,int);
void display(struct node *);
void reverse( struct node **);

int main()
{
struct node *p;
p=NULL;

append(&p,21);
append(&p,31);
append(&p,41);
append(&p,51);
append(&p,61);

display(p);
reverse(&p);
display(p);

return 0;
}

void append(struct node **q, int num)
{
struct node *temp,*r;
if (*q==NULL)
{
temp=(struct node *)malloc(sizeof(struct node*));
temp->data=num;
temp->prev=NULL;
temp->next=NULL;
*q=temp;
}
else
{
temp=*q;

while(temp->next!=NULL)
temp=temp->next;

r=(struct node *)malloc(sizeof(struct node *));
r->data=num;
temp->next=r;
r->next=NULL;
r->prev=temp;
}
}

void display(struct node *q)
{
while(q!=NULL)
{
printf("%d \t",q->data);
q=q->next;
}
printf("\n");
}

void reverse(struct node **q)
{
struct node *temp,*current;
current=*q;
temp=NULL;
while(current!=NULL)
{
current->prev=current->next;
current->next=temp;
temp=current;
current=current->prev;
}
*q=temp;

}

void reverse(node * & start){

if(start==NULL) return;
node *ptr1,*ptr2;
ptr1=start->next;
start->next=NULL;
while(ptr1){
ptr2=ptr1->next;
ptr1->next=ptr1->prev;
ptr1->prev=NULL;
ptr1->next->prev=ptr1;
start=ptr1;
ptr1=ptr2;
}

}

void reverse(node * & start){
	
	if(start==NULL) return;
	node *ptr1,*ptr2;
	ptr1=start->next;
	start->next=NULL;
	while(ptr1){
		ptr2=ptr1->next;
		ptr1->next=ptr1->prev;
		ptr1->prev=NULL;
		ptr1->next->prev=ptr1;
		start=ptr1;
		ptr1=ptr2;
	}

}