Skip to content
Related Articles

Related Articles

C++ Program to Rotate Linked List block wise

View Discussion
Improve Article
Save Article
  • Last Updated : 11 Jan, 2022
View Discussion
Improve Article
Save Article

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!


My Personal Notes arrow_drop_up
Recommended Articles
Page :

Start Your Coding Journey Now!