## Given a linkedlist and an integer k, write a function to rotate the linked list counter clockwise by k nodes.

### Example

**Current List is :-**

23 ->1 ->50 ->15 ->16 ->6

K = 4

**After rotating the linked list counter clockwise by k nodes**

16 ->6 ->23 ->1 ->50 ->15

In the above example you can see that the list is rotated counter clockwise by 4 nodes. Consider 16, it is moved left(ie counter clockwise) by 4 nodes. Simlarly to other elements.

**Time Complexity : O(n)**

## Algorithm

**1.** Traverse the first k nodes, and store pointer to the Kth node. ie, temp

**2.** Store the Kth node in a KthNode pointer ie, KthNode = temp

**3.** Move temp to the last node

**4.** Change next of last node to head ie, temp->next = head

**5.** Change head to the next of KthNode ie, head = KthNode->next

**6.** Point next of KthNode to NULL ie, KthNode->next = NULL

The above algorithm can be clearly explained in below diagram

## C++ Program

```
#include <bits/stdc++.h>
using namespace std;
struct LLNode{
int data;
LLNode *next;
};
//This funnction will rotate the list counter clockwise by k nodes
void rotate(LLNode** head, int k)
{
LLNode* temp = *head;
int count = 1;
if (k==0)
{
return ;
}
//Pointing temp to the kth node
while(count<k && temp != NULL) {
temp = temp->next;
count++;
}
//If it is NULL then dont rotate
if (temp==NULL)
{
return;
}
//point KthNode to temp
LLNode* KthNode = temp;
//Move temp to the last node
while(temp->next != NULL) {
temp = temp->next;
}
//point next of temp to the head
temp->next = *head;
//change head to the next of Kth node
*head = KthNode->next;
//Point next of KthNode to NULL
KthNode->next = NULL;
}
void insertAtBeginning(LLNode**head,int dataToBeInserted)
{
LLNode*curr=new LLNode;
//make a new node with this data and next pointing to NULL
curr->data=dataToBeInserted;
curr->next=NULL;
if(*head==NULL) //if list is empty then set the current formed node as head of list
*head=curr;
else //make the next of the current node point to the present head and make the current node as the new head
{
curr->next=*head;
*head=curr;
}
//O(1) constant time
}
void display(LLNode**head)
{
LLNode*temp=*head;
while(temp!=NULL) //till the list ends (NULL marks ending of list)
{
if(temp->next!=NULL)
cout<<temp->data<<" ->";
else
cout<<temp->data;
temp=temp->next; //move to next node
}
//O(number of nodes)
cout<<endl;
}
int main()
{
LLNode *head = NULL; //initial list has no elements
int k = 4;
insertAtBeginning(&head,6);
insertAtBeginning(&head,16);
insertAtBeginning(&head,15);
insertAtBeginning(&head,50);
insertAtBeginning(&head,1);
insertAtBeginning(&head,23);
cout<<"\nCurrent List is :-\n";
display(&head);
rotate(&head, k);
cout<<"After rotating the linked list counter clockwise by k nodes"<<endl;
display(&head);
return 0;
}
```

Try It

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