C++ Program to Rotate Linked List block wise

Given a Linked List of length n and block length k rotate in a circular manner towards right/left each block by a number d. If d is positive rotate towards right else rotate towards left.

Examples:

Input: 1->2->3->4->5->6->7->8->9->NULL, 
        k = 3 
        d = 1
Output: 3->1->2->6->4->5->9->7->8->NULL
Explanation: Here blocks of size 3 are
rotated towards right(as d is positive) 
by 1.
 
Input: 1->2->3->4->5->6->7->8->9->10->
               11->12->13->14->15->NULL, 
        k = 4 
        d = -1
Output: 2->3->4->1->6->7->8->5->10->11
             ->12->9->14->15->13->NULL
Explanation: Here, at the end of linked 
list, remaining nodes are less than k, i.e.
only three nodes are left while k is 4. 
Rotate those 3 nodes also by d.

Prerequisite: Rotate a linked list
The idea is if the absolute value of d is greater than the value of k, then rotate the link list by d % k times. If d is 0, no need to rotate the linked list at all. 

C++

// C++ program to rotate a linked list
// block wise
#include<bits/stdc++.h>
using namespace std;

// Link list node
class Node
{
    public:
    int data;
    Node* next;
};

// Recursive function to rotate
// one block
Node* rotateHelper(Node* blockHead,
                   Node* blockTail,
                   int d, Node** tail,
                   int k)
{
    if (d == 0)
        return blockHead;

    // Rotate Clockwise
    if (d > 0)
    {
        Node* temp = blockHead;
        for (int i = 1; temp->next->next &&
                 i < k - 1; i++)
            temp = temp->next;

        blockTail->next = blockHead;
        *tail = temp;
        return rotateHelper(blockTail, temp,
                            d - 1, tail, k);
    }

    // Rotate anti-Clockwise
    if (d < 0)
    {
        blockTail->next = blockHead;
        *tail = blockHead;
        return rotateHelper(blockHead->next,
                            blockHead, d + 1,
                            tail, k);
    }
}

// Function to rotate the linked list
// block wise
Node* rotateByBlocks(Node* head,
                     int k, int d)
{
    // If length is 0 or 1 return head
    if (!head || !head->next)
        return head;

    // if degree of rotation is 0,
    // return head
    if (d == 0)
        return head;

    Node* temp = head, *tail = NULL;

    // Traverse upto last element of
    // this block
    int i;
    for (i = 1; temp->next && i < k; i++)
         temp = temp->next;

    // Storing the first node of next block
    Node* nextBlock = temp->next;

    // If nodes of this block are less than k.
    // Rotate this block also
    if (i < k)
        head = rotateHelper(head, temp,
                            d % k, &tail, i);
    else
        head = rotateHelper(head, temp,
                            d % k, &tail, k);

    // Append the new head of next block to
    // the tail of this block
    tail->next = rotateByBlocks(nextBlock,
                                k, d % k);

    // return head of updated Linked List
    return head;
}

// UTILITY FUNCTIONS
// Function to push a node
void push(Node** head_ref,
          int new_data)
{
    Node* new_node = new Node;
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}

// Function to print linked list
void printList(Node* node)
{
    while (node != NULL)
    {
        cout << node->data << " ";
        node = node->next;
    }
}

// Driver code
int main()
{
    // Start with the empty list
    Node* head = NULL;

    // Create a list 1->2->3->4->5->
    // 6->7->8->9->NULL
    for (int i = 9; i > 0; i -= 1)
        push(&head, i);

    cout <<
    "Given linked list ";
    printList(head);

    // k is block size and d is number
    // of rotations in every block.
    int k = 3, d = 2;
    head = rotateByBlocks(head, k, d);

    cout <<
    "Rotated by blocks Linked list ";
    printList(head);

    return (0);
}
// This is code is contributed by rathbhupendra

Output:

Given linked list 
1 2 3 4 5 6 7 8 9 
Rotated by blocks Linked list 
2 3 1 5 6 4 8 9 7

Please refer complete article on Rotate Linked List block wise for more details!