Remove every k-th node of the linked list

Given a singly linked list, Your task is to remove every K-th node of the linked list. Assume that K is always less than or equal to length of Linked List.

Examples :

Input : 1->2->3->4->5->6->7->8  
        k = 3
Output : 1->2->4->5->7->8
As 3 is the k-th node after its deletion list 
would be 1->2->4->5->6->7->8
And now 4 is the starting node then from it, 6 
would be the k-th node. So no other kth node 
could be there.So, final list is:
1->2->4->5->7->8.

Input: 1->2->3->4->5->6  
       k = 1
Output: Empty list 
All nodes need to be deleted

The idea is to traverse the list from the beginning and keep track of nodes visited after the last deletion. Whenever count becomes k, delete the current node and reset the count as 0.

(1) Traverse list and do following
   (a) Count node before deletion.
   (b) If (count == k) that means current 
        node is to be deleted.
      (i)  Delete current node i.e. do

          //  assign address of next node of 
          // current node to the previous node
          // of the current node.
          prev->next = ptr->next i.e.

       (ii) Reset count as 0, i.e., do count = 0.
   (c) Update prev node if count != 0 and if
       count is 0 that means that node is a
       starting point.
   (d) Update ptr and continue until all 
       k-th node gets deleted.

Below is the implementation. 

C++

// C++ program to delete every k-th Node of
// a singly linked list.
#include<bits/stdc++.h>
using namespace std;

/* Linked list Node */
struct Node
{
    int data;
    struct Node* next;
};

// To remove complete list (Needed for
// case when k is 1)
void freeList(Node *node)
{
    while (node != NULL)
    {
        Node *next = node->next;
        delete (node);
        node  = next;
    }
}

// Deletes every k-th node and returns head
// of modified list.
Node *deleteKthNode(struct Node *head, int k)
{
    // If linked list is empty
    if (head == NULL)
        return NULL;

    if (k == 1)
    {
       freeList(head);
       return NULL;
    }

    // Initialize ptr and prev before starting
    // traversal.
    struct Node *ptr = head, *prev = NULL;

    // Traverse list and delete every k-th node
    int count = 0;
    while (ptr != NULL)
    {
        // increment Node count
        count++;

        // check if count is equal to k
        // if yes, then delete current Node
        if (k == count)
        {
            // put the next of current Node in
            // the next of previous Node
            delete(prev->next);
            prev->next = ptr->next;

            // set count = 0 to reach further
            // k-th Node
            count = 0;
        }

        // update prev if count is not 0
        if (count != 0)
            prev = ptr;

        ptr = prev->next;
    }

    return head;
}

/* Function to print linked list */
void displayList(struct Node *head)
{
    struct Node *temp = head;
    while (temp != NULL)
    {
        cout<<temp->data<<" ";
        temp = temp->next;
    }
}

// Utility function to create a new node.
struct Node *newNode(int x)
{
    Node *temp = new Node;
    temp->data = x;
    temp->next = NULL;
    return temp;
}

/* Driver program to test count function*/
int main()
{
    /* Start with the empty list */
    struct Node* head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(3);
    head->next->next->next = newNode(4);
    head->next->next->next->next = newNode(5);
    head->next->next->next->next->next = newNode(6);
    head->next->next->next->next->next->next =
                                        newNode(7);
    head->next->next->next->next->next->next->next =
                                        newNode(8);

    int k = 3;
    head = deleteKthNode(head, k);

    displayList(head);

    return 0;
}

Java

// Java program to delete every k-th Node
// of a singly linked list.
class GFG
{

/* Linked list Node */
static class Node
{
    int data;
    Node next;
}

// To remove complete list (Needed for
// case when k is 1)
static Node freeList(Node node)
{
    while (node != null)
    {
        Node next = node.next;
        node = next;
    }
    return node;
}

// Deletes every k-th node and
// returns head of modified list.
static Node deleteKthNode(Node head, int k)
{
    // If linked list is empty
    if (head == null)
        return null;

    if (k == 1)
    {
        head = freeList(head);
        return null;
    }

    // Initialize ptr and prev before
    // starting traversal.
    Node ptr = head, prev = null;

    // Traverse list and delete
    // every k-th node
    int count = 0;
    while (ptr != null)
    {
        // increment Node count
        count++;

        // check if count is equal to k
        // if yes, then delete current Node
        if (k == count)
        {
            // put the next of current Node in
            // the next of previous Node
            prev.next = ptr.next;

            // set count = 0 to reach further
            // k-th Node
            count = 0;
        }

        // update prev if count is not 0
        if (count != 0)
            prev = ptr;

        ptr = prev.next;
    }
    return head;
}

/* Function to print linked list */
static void displayList(Node head)
{
    Node temp = head;
    while (temp != null)
    {
        System.out.print(temp.data + " ");
        temp = temp.next;
    }
}

// Utility function to create a new node.
static Node newNode(int x)
{
    Node temp = new Node();
    temp.data = x;
    temp.next = null;
    return temp;
}

// Driver Code
public static void main(String args[])
{
    /* Start with the empty list */
    Node head = newNode(1);
    head.next = newNode(2);
    head.next.next = newNode(3);
    head.next.next.next = newNode(4);
    head.next.next.next.next = newNode(5);
    head.next.next.next.next.next = newNode(6);
    head.next.next.next.next.next.next =
                                        newNode(7);
    head.next.next.next.next.next.next.next =
                                        newNode(8);

    int k = 3;
    head = deleteKthNode(head, k);

    displayList(head);
}
}

// This code is contributed by Arnab Kundu

Python3

# Python3 program to delete every k-th Node
# of a singly linked list.
import math

# Linked list Node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

# To remove complete list (Needed for
# case when k is 1)
def freeList(node):
    while (node != None):
        next = node.next
        node = next
    return node

# Deletes every k-th node and
# returns head of modified list.
def deleteKthNode(head, k):

    # If linked list is empty
    if (head == None):
        return None

    if (k == 1):
        freeList(head)
        return None

    # Initialize ptr and prev before
    # starting traversal.
    ptr = head
    prev = None

    # Traverse list and delete every k-th node
    count = 0
    while (ptr != None):

        # increment Node count
        count = count + 1

        # check if count is equal to k
        # if yes, then delete current Node
        if (k == count):

            # put the next of current Node in
            # the next of previous Node
            # delete(prev.next)
            prev.next = ptr.next

            # set count = 0 to reach further
            # k-th Node
            count = 0

        # update prev if count is not 0
        if (count != 0):
            prev = ptr

        ptr = prev.next

    return head

# Function to print linked list
def displayList(head):
    temp = head
    while (temp != None):
        print(temp.data, end = ' ')
        temp = temp.next

# Utility function to create a new node.
def newNode( x):
    temp = Node(x)
    temp.data = x
    temp.next = None
    return temp

# Driver Code
if __name__=='__main__':

    # Start with the empty list
    head = newNode(1)
    head.next = newNode(2)
    head.next.next = newNode(3)
    head.next.next.next = newNode(4)
    head.next.next.next.next = newNode(5)
    head.next.next.next.next.next = newNode(6)
    head.next.next.next.next.next.next = newNode(7)
    head.next.next.next.next.next.next.next = newNode(8)

    k = 3
    head = deleteKthNode(head, k)

    displayList(head)

# This code is contributed by Srathore

C#

// C# program to delete every k-th Node
// of a singly linked list.
using System;

class GFG
{

/* Linked list Node */
public class Node
{
    public int data;
    public Node next;
}

// To remove complete list (Needed for
// case when k is 1)
static Node freeList(Node node)
{
    while (node != null)
    {
        Node next = node.next;
        node = next;
    }
    return node;
}

// Deletes every k-th node and
// returns head of modified list.
static Node deleteKthNode(Node head, int k)
{
    // If linked list is empty
    if (head == null)
        return null;

    if (k == 1)
    {
        head = freeList(head);
        return null;
    }

    // Initialize ptr and prev before
    // starting traversal.
    Node ptr = head, prev = null;

    // Traverse list and delete
    // every k-th node
    int count = 0;
    while (ptr != null)
    {
        // increment Node count
        count++;

        // check if count is equal to k
        // if yes, then delete current Node
        if (k == count)
        {
            // put the next of current Node in
            // the next of previous Node
            prev.next = ptr.next;

            // set count = 0 to reach further
            // k-th Node
            count = 0;
        }

        // update prev if count is not 0
        if (count != 0)
            prev = ptr;

        ptr = prev.next;
    }
    return head;
}

/* Function to print linked list */
static void displayList(Node head)
{
    Node temp = head;
    while (temp != null)
    {
        Console.Write(temp.data + " ");
        temp = temp.next;
    }
}

// Utility function to create a new node.
static Node newNode(int x)
{
    Node temp = new Node();
    temp.data = x;
    temp.next = null;
    return temp;
}

// Driver Code
public static void Main(String []args)
{
    /* Start with the empty list */
    Node head = newNode(1);
    head.next = newNode(2);
    head.next.next = newNode(3);
    head.next.next.next = newNode(4);
    head.next.next.next.next = newNode(5);
    head.next.next.next.next.next = newNode(6);
    head.next.next.next.next.next.next = newNode(7);
    head.next.next.next.next.next.next.next = newNode(8);

    int k = 3;
    head = deleteKthNode(head, k);

    displayList(head);
}
}

// This code is contributed by PrinciRaj1992

Javascript

<script>

// Javascript program to delete every k-th Node
// of a singly linked list.
/* Linked list Node */
class Node {
    constructor() {
        this.data = 0;
        this.next = null;
    }
}


    // To remove complete list (Needed for
    // case when k is 1)
    function freeList( node) {
        while (node != null) {
             next = node.next;
            node = next;
        }
        return node;
    }

    // Deletes every k-th node and
    // returns head of modified list.
    function deleteKthNode( head , k) {
        // If linked list is empty
        if (head == null)
            return null;

        if (k == 1) {
            head = freeList(head);
            return null;
        }

        // Initialize ptr and prev before
        // starting traversal.
        var ptr = head, prev = null;

        // Traverse list and delete
        // every k-th node
        var count = 0;
        while (ptr != null) {
            // increment Node count
            count++;

            // check if count is equal to k
            // if yes, then delete current Node
            if (k == count) {
                // put the next of current Node in
                // the next of previous Node
                prev.next = ptr.next;

                // set count = 0 to reach further
                // k-th Node
                count = 0;
            }

            // update prev if count is not 0
            if (count != 0)
                prev = ptr;

            ptr = prev.next;
        }
        return head;
    }

    /* Function to print linked list */
    function displayList( head) {
         temp = head;
        while (temp != null) {
            document.write(temp.data + " ");
            temp = temp.next;
        }
    }

    // Utility function to create a new node.
    function newNode(x) {
         temp = new Node();
        temp.data = x;
        temp.next = null;
        return temp;
    }

    // Driver Code

        /* Start with the empty list */
         head = newNode(1);
        head.next = newNode(2);
        head.next.next = newNode(3);
        head.next.next.next = newNode(4);
        head.next.next.next.next = newNode(5);
        head.next.next.next.next.next = newNode(6);
        head.next.next.next.next.next.next = newNode(7);
        head.next.next.next.next.next.next.next = newNode(8);

        var k = 3;
        head = deleteKthNode(head, k);

        displayList(head);

// This code contributed by umadevi9616

</script>

Output

1 2 1 

Time Complexity : O(n) 
Auxiliary Space : O(1)

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