C++ Program to Rotate Linked List block wise

// 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