Delete every Kth node from circular linked list


Delete every kth Node from a circular linked list until only one node is left. Also print the intermediate lists.

Examples:

Input : n=4, k=2, list = 1->2->3->4
Output : 
1->2->3->4->1
1->2->4->1
2->4->2
2->2

Input : n=9, k=4, list = 1->2->3->4->5->6->7->8->9
Output :
1->2->3->4->5->6->7->8->9->1
1->2->3->4->6->7->8->9->1
1->2->3->4->6->7->8->1
1->2->3->6->7->8->1
2->3->6->7->8->2
2->3->6->8->2
2->3->8->2
2->3->2
2->2

Algorithm
Repeat the following steps until there is only one node left in the list.
Case 1: List is empty.
If the list is empty, simply return.



Case 2: List has only one node.
If the list has only one node left, we will print the list and return as our goal is reached.

Case 3: List has more than one nodes.
Define two pointers curr and prev and initialize the pointer curr with the head node.
Traverse the list using curr pointer by iterating it k times.

  • Node to be deleted is the first node of the list.
    Condition to check this( curr == head && curr->next == head).
    If yes, then move prev until it reaches the last node. After prev reaches the last node, set head = head -> next and prev -> next = head. Delete curr.
  • Node to be deleted is the last node in the list.
    Condition to check this is (curr -> next == head).
    If curr is the last node. Set prev -> next = head and delete the node curr by free(curr).
  • Node to be deleted is neither the first node nor the last node, then set prev -> next = temp -> next and delete curr.

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ program to delete every kth Node from
// circular linked list.
#include <bits/stdc++.h>
using namespace std;
  
/* structure for a Node */
struct Node {
    int data;
    Node* next;
    Node(int x)
    {
        data = x;
        next = NULL;
    }
};
  
/*Utility function to print the circular linked list*/
void printList(Node* head)
{
    if (head == NULL)
        return;
    Node* temp = head;
    do {
        cout << temp->data << "->";
        temp = temp->next;
    } while (temp != head);
    cout << head->data << endl;
}
  
/*Function to delete every kth Node*/
void deleteK(Node** head_ref, int k)
{
    Node* head = *head_ref;
  
    // If list is empty, simply return.
    if (head == NULL)
        return;
  
    // take two pointers - current and previous
    Node *curr = head, *prev;
    while (true) {
  
        // Check if Node is the only Node\
        // If yes, we reached the goal, therefore 
        // return.
        if (curr->next == head && curr == head)
            break;
  
        // Print intermediate list.
        printList(head);
  
        // If more than one Node present in the list,
        // Make previous pointer point to current
        // Iterate current pointer k times,
        // i.e. current Node is to be deleted.
        for (int i = 0; i < k; i++) {
            prev = curr;
            curr = curr->next;
        }
  
        // If Node to be deleted is head
        if (curr == head) {
            prev = head;
            while (prev->next != head)
                prev = prev->next;
            head = curr->next;
            prev->next = head;
            *head_ref = head;
            free(curr);
        }
  
        // If Node to be deleted is last Node.
        else if (curr->next == head) {
            prev->next = head;
            free(curr);
        }
        else {
            prev->next = curr->next;
            free(curr);
        }
    }
}
  
/* Function to insert a Node at the end of 
a Circular linked list */
void insertNode(Node** head_ref, int x)
{
    // Create a new Node
    Node* head = *head_ref;
    Node* temp = new Node(x);
  
    // if the list is empty, make the new Node head
    // Also, it will point to itself.
    if (head == NULL) {
        temp->next = temp;
        *head_ref = temp;
    }
  
    // traverse the list to reach the last Node 
    // and insert the Node
    else {
        Node* temp1 = head;
        while (temp1->next != head)
            temp1 = temp1->next;
        temp1->next = temp;
        temp->next = head;
    }
}
  
/* Driver program to test above functions */
int main()
{
    // insert Nodes in the circular linked list
    struct Node* head = NULL;
    insertNode(&head, 1);
    insertNode(&head, 2);
    insertNode(&head, 3);
    insertNode(&head, 4);
    insertNode(&head, 5);
    insertNode(&head, 6);
    insertNode(&head, 7);
    insertNode(&head, 8);
    insertNode(&head, 9);
  
    int k = 4;
  
    // Delete every kth Node from the
    // circular linked list.
    deleteK(&head, k);
  
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to delete every kth Node from 
// circular linked list. 
class GFG
{
      
/* structure for a Node */
static class Node
    int data; 
    Node next; 
    Node(int x) 
    
        data = x; 
        next = null
    
}; 
  
/*Utility function to print 
the 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); 
    System.out.println(head.data ); 
  
/*Function to delete every kth Node*/
static Node deleteK(Node head_ref, int k) 
    Node head = head_ref; 
  
    // If list is empty, simply return. 
    if (head == null
        return null
  
    // take two pointers - current and previous 
    Node curr = head, prev=null
    while (true
    
  
        // Check if Node is the only Node\ 
        // If yes, we reached the goal, therefore 
        // return. 
        if (curr.next == head && curr == head) 
            break
  
        // Print intermediate list. 
        printList(head); 
  
        // If more than one Node present in the list, 
        // Make previous pointer point to current 
        // Iterate current pointer k times, 
        // i.e. current Node is to be deleted. 
        for (int i = 0; i < k; i++) 
        
            prev = curr; 
            curr = curr.next; 
        
  
        // If Node to be deleted is head 
        if (curr == head) 
        
            prev = head; 
            while (prev.next != head) 
                prev = prev.next; 
            head = curr.next; 
            prev.next = head; 
            head_ref = head; 
        
  
        // If Node to be deleted is last Node. 
        else if (curr.next == head) 
        
            prev.next = head; 
        
        else
        
            prev.next = curr.next; 
        
    
    return head;
  
/* Function to insert a Node at the end of 
a Circular linked list */
static Node insertNode(Node head_ref, int x) 
    // Create a new Node 
    Node head = head_ref; 
    Node temp = new Node(x); 
  
    // if the list is empty, make the new Node head 
    // Also, it will point to itself. 
    if (head == null
    
        temp.next = temp; 
        head_ref = temp; 
        return head_ref;
    
  
    // traverse the list to reach the last Node 
    // and insert the Node 
    else 
    
        Node temp1 = head; 
        while (temp1.next != head) 
            temp1 = temp1.next; 
        temp1.next = temp; 
        temp.next = head; 
    
    return head;
  
/* Driver code */
public static void main(String args[])
    // insert Nodes in the circular linked list 
    Node head = null
    head = insertNode(head, 1); 
    head = insertNode(head, 2); 
    head = insertNode(head, 3); 
    head = insertNode(head, 4); 
    head = insertNode(head, 5); 
    head = insertNode(head, 6); 
    head = insertNode(head, 7); 
    head = insertNode(head, 8); 
    head = insertNode(head, 9); 
  
    int k = 4
  
    // Delete every kth Node from the 
    // circular linked list. 
    head = deleteK(head, k); 
}
  
// This code is contributed by Arnab Kundu

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program to delete every kth Node from 
// circular linked list.
using System;
  
class GFG
{
      
/* structure for a Node */
public class Node
    public int data; 
    public Node next; 
    public Node(int x) 
    
        data = x; 
        next = null
    
}; 
  
/*Utility function to print 
the 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); 
    Console.WriteLine(head.data ); 
  
/*Function to delete every kth Node*/
static Node deleteK(Node head_ref, int k) 
    Node head = head_ref; 
  
    // If list is empty, simply return. 
    if (head == null
        return null
  
    // take two pointers - current and previous 
    Node curr = head, prev = null
    while (true
    
  
        // Check if Node is the only Node\ 
        // If yes, we reached the goal, therefore 
        // return. 
        if (curr.next == head && curr == head) 
            break
  
        // Print intermediate list. 
        printList(head); 
  
        // If more than one Node present in the list, 
        // Make previous pointer point to current 
        // Iterate current pointer k times, 
        // i.e. current Node is to be deleted. 
        for (int i = 0; i < k; i++) 
        
            prev = curr; 
            curr = curr.next; 
        
  
        // If Node to be deleted is head 
        if (curr == head) 
        
            prev = head; 
            while (prev.next != head) 
                prev = prev.next; 
            head = curr.next; 
            prev.next = head; 
            head_ref = head; 
        
  
        // If Node to be deleted is last Node. 
        else if (curr.next == head) 
        
            prev.next = head; 
        
        else
        
            prev.next = curr.next; 
        
    
    return head;
  
/* Function to insert a Node at the end of 
a Circular linked list */
static Node insertNode(Node head_ref, int x) 
    // Create a new Node 
    Node head = head_ref; 
    Node temp = new Node(x); 
  
    // if the list is empty, make the new Node head 
    // Also, it will point to itself. 
    if (head == null
    
        temp.next = temp; 
        head_ref = temp; 
        return head_ref;
    
  
    // traverse the list to reach the last Node 
    // and insert the Node 
    else
    
        Node temp1 = head; 
        while (temp1.next != head) 
            temp1 = temp1.next; 
        temp1.next = temp; 
        temp.next = head; 
    
    return head;
  
/* Driver code */
public static void Main(String []args)
    // insert Nodes in the circular linked list 
    Node head = null
    head = insertNode(head, 1); 
    head = insertNode(head, 2); 
    head = insertNode(head, 3); 
    head = insertNode(head, 4); 
    head = insertNode(head, 5); 
    head = insertNode(head, 6); 
    head = insertNode(head, 7); 
    head = insertNode(head, 8); 
    head = insertNode(head, 9); 
  
    int k = 4; 
  
    // Delete every kth Node from the 
    // circular linked list. 
    head = deleteK(head, k); 
}
  
// This code has been contributed by 29AjayKumar

chevron_right


Output:

1->2->3->4->5->6->7->8->9->1
1->2->3->4->6->7->8->9->1
1->2->3->4->6->7->8->1
1->2->3->6->7->8->1
2->3->6->7->8->2
2->3->6->8->2
2->3->8->2
2->3->2
2->2


My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.



Improved By : andrew1234, 29AjayKumar