Question

I am preparing for a technical interview and I am stuck at writing this program to reverse every k nodes of a linked list.

For example

1->2->3->4->5->6 //Linked List
2->1->4->3->6->5 //Output for k=2

EDIT:

Here is my code. I get only 6->5 as output.

struct node* recrev(struct node* noode,int c)
{
 struct node* root=noode,*temp,*final,*prev=NULL;
 int count=0;
 while(root!=NULL && count<c)
 {
  count++;
  temp=root->link;
  root->link=prev;
  prev=root;
  root=temp;
 }
 if(temp!=NULL)
   noode->link=recrev(temp,c);
 else
   return prev;

}

Any help is appreciated. Thanks.

EDIT: I tried to implement Eran Zimmerman’s Algorithm as below.

struct node* rev(struct node* root,int c)
{
 struct node* first=root,*prev,*remaining=NULL;
 int count=0;
 while(first!=NULL && count<c)
 {

    count++;
    prev=first->link;
    first->link=remaining;
    remaining=first;
    first=prev;
 }
 return remaining;
}
struct node* recc(struct node* root,int c)
{
 struct node* final,*temp,*n=root,*t;
 int count=0;
 while(n!=NULL)
 {
       count=0;
       temp=rev(n,c);
       final=temp;


    while(n!=NULL && count<c)
    {   
     printf("inside while: %c\n",n->data);  // This gets printed only once
     if(n->link==NULL) printf("NULL");    //During first iteration itself NULL gets printed
        n=n->link;
        final=final->link;
        count++;
    }

 }
 final->link=NULL;
 return final;
}

Answer 1

I like you recursion, although it may be not the best solution. I can see from your code that you think it deep when you design it. You’re just one step away from the answer.

Cause: You forget to return the new root node in your recursion case.

if(temp!=NULL)
   noode->link=recrev(temp,c);
   // You need return the new root node here
   // which in this case is prev:
   // return prev;
 else
   return prev;