Simpler and faster code for reversing list? - c

Question

I wrote the code for reversing a doubly linked list containing words in each node, which works perfectly fine.
My teacher says the algorithm is difficult to understand and the code as a whole could be made more efficient(reducing overhead and memory consumption). What changes can i make to the code/the reversing algorithm?
Also is there a way i could input the sentence without having to ask the number of words in advance? Here is the code:
#include<stdio.h>
#include<conio.h>
#include<string.h>
typedef struct NODE
{
char *item;
struct NODE *next;
struct NODE *prev;
}NODE;
void Insert(char data[],NODE **List)
{
NODE *temp,*last;
last=(*List);
temp=(NODE*)malloc(sizeof(NODE));
temp->item=(char*)malloc(strlen(data));
temp->item=data;
temp->next=NULL;
temp->prev=NULL;
if((*List)->item==NULL)
(*List)=temp;
else
{
while(last->next!=NULL)
last=last->next;
temp->prev=last;
last->next=temp;
last=temp;
}
}
void Reverse(NODE **List)
{
int flag1=0;
NODE *temp,*temp1,*last,*flag;
temp1=(NODE*)malloc(sizeof(NODE));
last=(*List);
while(last->next!=NULL)
last=last->next;
temp=last;
while(temp->prev!=NULL)
{
temp1->item=temp->item;
temp1->next=temp->next;
temp1->prev=temp->prev;
temp->next=temp->prev;
temp->prev=temp1->next;
temp=temp->next;
if(flag1==0)
{
flag1++;
flag=temp;
}
}
temp1->item=temp->item;
temp1->next=temp->next;
temp1->prev=temp->prev;
temp->next=NULL;
temp->prev=temp1->next;
(*List)=flag->prev;
free(temp1);
};
void display(NODE *List)
{
if(List->next==NULL)
{
printf("%s",List->item);
return;
}
NODE *temp;
temp=List;
do
{
printf("%s<-->",temp->item);
temp=temp->next;
}while(temp->next!=NULL);
printf("%s\n",temp->item);
}
int main()
{
int i=0,n;
char s[10][50];
NODE *List;
List=(NODE*)malloc(sizeof(NODE));
List->item=NULL;
List->next=NULL;
List->prev=NULL;
printf("Provide number of words(max 10): ");
scanf("%d",&n);
printf("Enter string of words for the list: ");
while(i<n)
{
scanf("%s",s[i]);
Insert(s[i],&List);
i++;
}
printf("\nOriginal List is: ");
display(List);
Reverse(&List);
printf("\nReversed List is: ");
display(List);
getch();
return 0;
}

Answer 1

Since it's a double-linked list you could just write two traversal functions. One forward and one reverse. Save two anchors for your list in your control structure: one for the first element and one for the last.

Answer 2

You can just swap the next and previous pointers for each node and swap tail and head pointers.

Answer 3

void reverse (struct node *ptr)
{
struct node *tmp, *kid;
if (!ptr) return;
for (kid = ptr->next; kid; kid = kid->prev) {
tmp = kid->prev;
kid->prev = kid->next;
kid->next = tmp;
}
for (kid = ptr->prev; kid; kid = kid->next) {
tmp = kid->prev;
kid->prev = kid->next;
kid->next = tmp;
}
tmp = ptr->prev;
ptr->prev = ptr->next;
ptr->next = tmp;
return;
}
Note: I removed the typedef. I hate typedefs.