C Program to Rotate Linked List block wise

// C program to rotate a linked list 
// block wise
#include <stdio.h>
#include <stdlib.h>

// Link list node 
struct Node 
{
    int data;
    struct Node* next;
};

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

    // Rotate Clockwise
    if (d > 0) 
    {
        struct 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
struct Node* rotateByBlocks(struct 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;

    struct 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
    struct 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(struct Node** head_ref, 
          int new_data)
{
    struct 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(struct Node* node)
{
    while (node != NULL) 
{
        printf("%d ", node->data);
        node = node->next;
    }
}

// Driver code
int main()
{
    // Start with the empty list 
    struct 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);

    printf("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);

    printf(
    "Rotated by blocks Linked list ");
    printList(head);

    return (0);
}