Reverse a circular linked list

Given a circular linked list of size n. The problem is to reverse the given circular linked list by changing links between the nodes.

Examples:
INPUT:
INPUT:

OUTPUT:
OUTPUT:



Approach: The approach is same as followed in reversing a singly linked list. Only here we have to make one more adjustment by linking the last node of the reversed list to the first node.

C++

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// C++ implementation to reverse
// a circular linked list
#include <bits/stdc++.h>
  
using namespace std;
  
// Linked list node
struct Node {
    int data;
    Node* next;
};
  
// function to get a new node
Node* getNode(int data)
{
    // allocate memory for node
    Node* newNode = new Node;
  
    // put in the data
    newNode->data = data;
    newNode->next = NULL;
    return newNode;
}
  
// Function to reverse the circular linked list
void reverse(Node** head_ref)
{
    // if list is empty
    if (*head_ref == NULL)
        return;
  
    // reverse procedure same as reversing a
    // singly linked list
    Node* prev = NULL;
    Node* current = *head_ref;
    Node* next;
    do {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    } while (current != (*head_ref));
  
    // adjutsing the links so as to make the
    // last node point to the first node
    (*head_ref)->next = prev;
    *head_ref = prev;
}
  
// Function to print circular linked list
void printList(Node* head)
{
    if (head == NULL)
        return;
  
    Node* temp = head;
    do {
        cout << temp->data << " ";
        temp = temp->next;
    } while (temp != head);
}
  
// Driver program to test above
int main()
{
    // Create a circular linked list
    // 1->2->3->4->1
    Node* head = getNode(1);
    head->next = getNode(2);
    head->next->next = getNode(3);
    head->next->next->next = getNode(4);
    head->next->next->next->next = head;
  
    cout << "Given circular linked list: ";
    printList(head);
  
    reverse(&head);
  
    cout << "\nReversed circular linked list: ";
    printList(head);
  
    return 0;
}

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Java

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// Java implementation to reverse 
// a circular linked list 
class GFG
{
  
// Linked list node 
static class Node
    int data; 
    Node next; 
}; 
  
// function to get a new node 
static Node getNode(int data) 
    // allocate memory for node 
    Node newNode = new Node(); 
  
    // put in the data 
    newNode.data = data; 
    newNode.next = null
    return newNode; 
  
// Function to reverse the circular linked list 
static Node reverse(Node head_ref) 
    // if list is empty 
    if (head_ref == null
        return null
  
    // reverse procedure same as reversing a 
    // singly linked list 
    Node prev = null
    Node current = head_ref; 
    Node next; 
    do 
    
        next = current.next; 
        current.next = prev; 
        prev = current; 
        current = next; 
    } while (current != (head_ref)); 
  
    // adjutsing the links so as to make the 
    // last node point to the first node 
    (head_ref).next = prev; 
    head_ref = prev; 
    return head_ref;
  
// Function to print circular linked list 
static void printList(Node head) 
    if (head == null
        return
  
    Node temp = head; 
    do
    
        System.out.print( temp.data + " "); 
        temp = temp.next; 
    } while (temp != head); 
  
// Driver code 
public static void main(String args[])
    // Create a circular linked list 
    // 1.2.3.4.1 
    Node head = getNode(1); 
    head.next = getNode(2); 
    head.next.next = getNode(3); 
    head.next.next.next = getNode(4); 
    head.next.next.next.next = head; 
  
    System.out.print("Given circular linked list: "); 
    printList(head); 
  
    head = reverse(head); 
  
    System.out.print("\nReversed circular linked list: "); 
    printList(head); 
  
}
  
// This code is contributed by Arnab Kundu

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C#

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// C# implementation to reverse 
// a circular linked list 
using System;
  
class GFG 
  
    // Linked list node 
    public class Node 
    
        public int data; 
        public Node next; 
    }; 
      
    // function to get a new node 
    static Node getNode(int data) 
    
        // allocate memory for node 
        Node newNode = new Node(); 
      
        // put in the data 
        newNode.data = data; 
        newNode.next = null
        return newNode; 
    
      
    // Function to reverse the circular linked list 
    static Node reverse(Node head_ref) 
    
        // if list is empty 
        if (head_ref == null
            return null
      
        // reverse procedure same as reversing a 
        // singly linked list 
        Node prev = null
        Node current = head_ref; 
        Node next; 
        do
        
            next = current.next; 
            current.next = prev; 
            prev = current; 
            current = next; 
        } while (current != (head_ref)); 
      
        // adjutsing the links so as to make the 
        // last node point to the first node 
        (head_ref).next = prev; 
        head_ref = prev; 
        return head_ref; 
    
      
    // Function to print circular linked list 
    static void printList(Node head) 
    
        if (head == null
            return
      
        Node temp = head; 
        do
        
            Console.Write( temp.data + " "); 
            temp = temp.next; 
        } while (temp != head); 
    
      
    // Driver code 
    public static void Main(String []args) 
    
        // Create a circular linked list 
        // 1.2.3.4.1 
        Node head = getNode(1); 
        head.next = getNode(2); 
        head.next.next = getNode(3); 
        head.next.next.next = getNode(4); 
        head.next.next.next.next = head; 
      
        Console.Write("Given circular linked list: "); 
        printList(head); 
      
        head = reverse(head); 
      
        Console.Write("\nReversed circular linked list: "); 
        printList(head); 
      
    
  
// This code contributed by Rajput-Ji

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Output:

Given circular linked list: 1 2 3 4
Reversed circular linked list: 4 3 2 1

Time Complexity: O(n)

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Improved By : andrew1234, Rajput-Ji



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