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Delete N nodes after M nodes of a linked list

  • Difficulty Level : Easy
  • Last Updated : 22 Oct, 2021

Given a linked list and two integers M and N. Traverse the linked list such that you retain M nodes then delete next N nodes, continue the same till end of the linked list.
Difficulty Level: Rookie 
Examples: 
 

Input:
M = 2, N = 2
Linked List: 1->2->3->4->5->6->7->8
Output:
Linked List: 1->2->5->6

Input:
M = 3, N = 2
Linked List: 1->2->3->4->5->6->7->8->9->10
Output:
Linked List: 1->2->3->6->7->8

Input:
M = 1, N = 1
Linked List: 1->2->3->4->5->6->7->8->9->10
Output:
Linked List: 1->3->5->7->9

 

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The main part of the problem is to maintain proper links between nodes, make sure that all corner cases are handled. Following is C implementation of function skipMdeleteN() that skips M nodes and delete N nodes till end of list. It is assumed that M cannot be 0. 
 

C++




// C++ program to delete N nodes
// after M nodes of a linked list
#include <bits/stdc++.h>
using namespace std;
 
// A linked list node
class Node
{
    public:
    int data;
    Node *next;
};
 
/* Function to insert a node at the beginning */
void push(Node ** head_ref, int new_data)
{
    /* allocate node */
    Node* new_node = new Node();
 
    /* put in the data */
    new_node->data = new_data;
 
    /* link the old list off the new node */
    new_node->next = (*head_ref);
 
    /* move the head to point to the new node */
    (*head_ref) = new_node;
}
 
/* Function to print linked list */
void printList(Node *head)
{
    Node *temp = head;
    while (temp != NULL)
    {
        cout<<temp->data<<" ";
        temp = temp->next;
    }
    cout<<endl;
}
 
// Function to skip M nodes and then
// delete N nodes of the linked list.
void skipMdeleteN(Node *head, int M, int N)
{
    Node *curr = head, *t;
    int count;
 
    // The main loop that traverses
    // through the whole list
    while (curr)
    {
        // Skip M nodes
        for (count = 1; count < M &&
                curr!= NULL; count++)
            curr = curr->next;
 
        // If we reached end of list, then return
        if (curr == NULL)
            return;
 
        // Start from next node and delete N nodes
        t = curr->next;
        for (count = 1; count<=N && t!= NULL; count++)
        {
            Node *temp = t;
            t = t->next;
            free(temp);
        }
         
        // Link the previous list with remaining nodes
        curr->next = t;
 
        // Set current pointer for next iteration
        curr = t;
    }
}
 
// Driver code
int main()
{
    /* Create following linked list
    1->2->3->4->5->6->7->8->9->10 */
    Node* head = NULL;
    int M=2, N=3;
    push(&head, 10);
    push(&head, 9);
    push(&head, 8);
    push(&head, 7);
    push(&head, 6);
    push(&head, 5);
    push(&head, 4);
    push(&head, 3);
    push(&head, 2);
    push(&head, 1);
 
    cout << "M = " << M<< " N = " << N << "\nGiven Linked list is :\n";
    printList(head);
 
    skipMdeleteN(head, M, N);
 
    cout<<"\nLinked list after deletion is :\n";
    printList(head);
 
    return 0;
}
 
// This code is contributed by rathbhupendra

C




// C program to delete N nodes after M nodes of a linked list
#include <stdio.h>
#include <stdlib.h>
 
// A linked list node
struct Node
{
    int data;
    struct Node *next;
};
 
/* Function to insert a node at the beginning */
void push(struct Node ** head_ref, int new_data)
{
    /* allocate node */
    struct Node* new_node = (struct Node*) malloc(sizeof(struct Node));
 
    /* put in the data  */
    new_node->data  = new_data;
 
    /* link the old list off the new node */
    new_node->next = (*head_ref);
 
    /* move the head to point to the new node */
    (*head_ref)  = new_node;
}
 
/* Function to print linked list */
void printList(struct Node *head)
{
    struct Node *temp = head;
    while (temp != NULL)
    {
        printf("%d ", temp->data);
        temp = temp->next;
    }
    printf("\n");
}
 
// Function to skip M nodes and then delete N nodes of the linked list.
void skipMdeleteN(struct Node  *head, int M, int N)
{
    struct Node *curr = head, *t;
    int count;
 
    // The main loop that traverses through the whole list
    while (curr)
    {
        // Skip M nodes
        for (count = 1; count<M && curr!= NULL; count++)
            curr = curr->next;
 
        // If we reached end of list, then return
        if (curr == NULL)
            return;
 
        // Start from next node and delete N nodes
        t = curr->next;
        for (count = 1; count<=N && t!= NULL; count++)
        {
            struct Node *temp = t;
            t = t->next;
            free(temp);
        }
        curr->next = t; // Link the previous list with remaining nodes
 
        // Set current pointer for next iteration
        curr = t;
    }
}
 
// Driver program to test above functions
int main()
{
    /* Create following linked list
      1->2->3->4->5->6->7->8->9->10 */
    struct Node* head = NULL;
    int M=2, N=3;
    push(&head, 10);
    push(&head, 9);
    push(&head, 8);
    push(&head, 7);
    push(&head, 6);
    push(&head, 5);
    push(&head, 4);
    push(&head, 3);
    push(&head, 2);
    push(&head, 1);
 
    printf("M = %d, N = %d \nGiven Linked list is :\n", M, N);
    printList(head);
 
    skipMdeleteN(head, M, N);
 
    printf("\nLinked list after deletion is :\n");
    printList(head);
 
    return 0;
}

Java




// Java program to delete N nodes
// after M nodes of a linked list
import java.util.*;
 
class GFG
{
 
// A linked list node
static class Node
{
    int data;
    Node next;
};
 
/* Function to insert a node at the beginning */
static Node push( Node head_ref, int new_data)
{
    /* allocate node */
    Node new_node = new Node();
 
    /* put in the data */
    new_node.data = new_data;
 
    /* link the old list off the new node */
    new_node.next = (head_ref);
 
    /* move the head to point to the new node */
    (head_ref) = new_node;
     
    return head_ref;
}
 
/* Function to print linked list */
static void printList( Node head)
{
    Node temp = head;
    while (temp != null)
    {
        System.out.printf("%d ", temp.data);
        temp = temp.next;
    }
    System.out.printf("\n");
}
 
// Function to skip M nodes and then
// delete N nodes of the linked list.
static void skipMdeleteN( Node head, int M, int N)
{
    Node curr = head, t;
    int count;
 
    // The main loop that traverses
    // through the whole list
    while (curr!=null)
    {
        // Skip M nodes
        for (count = 1; count < M && curr != null; count++)
            curr = curr.next;
 
        // If we reached end of list, then return
        if (curr == null)
            return;
 
        // Start from next node and delete N nodes
        t = curr.next;
        for (count = 1; count <= N && t != null; count++)
        {
            Node temp = t;
            t = t.next;
        }
         
        // Link the previous list with remaining nodes
        curr.next = t;
 
        // Set current pointer for next iteration
        curr = t;
    }
}
 
// Driver code
public static void main(String args[])
{
    /* Create following linked list
    1.2.3.4.5.6.7.8.9.10 */
    Node head = null;
    int M=2, N=3;
    head=push(head, 10);
    head=push(head, 9);
    head=push(head, 8);
    head=push(head, 7);
    head=push(head, 6);
    head=push(head, 5);
    head=push(head, 4);
    head=push(head, 3);
    head=push(head, 2);
    head=push(head, 1);
 
    System.out.printf("M = %d, N = %d \nGiven" +
                        "Linked list is :\n", M, N);
    printList(head);
 
    skipMdeleteN(head, M, N);
 
    System.out.printf("\nLinked list after deletion is :\n");
    printList(head);
}
}
 
// This code is contributed by Arnab Kundu

Python




# Python program to delete M nodes after N nodes
 
# Node class
class Node:
 
    # Constructor to initialize the node object
    def __init__(self, data):
        self.data = data
        self.next = None
 
class LinkedList:
 
    # Function to initialize head
    def __init__(self):
        self.head = None
 
    # Function to insert a new node at the beginning
    def push(self, new_data):
        new_node = Node(new_data)
        new_node.next = self.head
        self.head = new_node
 
    # Utility function to print the linked LinkedList
    def printList(self):
        temp = self.head
        while(temp):
            print temp.data,
            temp = temp.next
 
    def skipMdeleteN(self, M, N):
        curr = self.head
         
        # The main loop that traverses through the
        # whole list
        while(curr):
            # Skip M nodes
            for count in range(1, M):
                if curr is None:
                    return
                curr = curr.next
                     
            if curr is None :
                return
 
            # Start from next node and delete N nodes
            t = curr.next
            for count in range(1, N+1):
                if t is None:
                    break
                t = t.next
     
            # Link the previous list with remaining nodes
            curr.next = t
            # Set Current pointer for next iteration
            curr = t
 
# Driver program to test above function
 
# Create following linked list
# 1->2->3->4->5->6->7->8->9->10
llist = LinkedList()
M = 2
N = 3
llist.push(10)
llist.push(9)
llist.push(8)
llist.push(7)
llist.push(6)
llist.push(5)
llist.push(4)
llist.push(3)
llist.push(2)
llist.push(1)
 
print "M = %d, N = %d\nGiven Linked List is:" %(M, N)
llist.printList()
print
 
llist.skipMdeleteN(M, N)
 
print "\nLinked list after deletion is"
llist.printList()
 
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

C#




// C# program to delete N nodes
// after M nodes of a linked list
using System;
 
class GFG
{
 
// A linked list node
public class Node
{
    public int data;
    public Node next;
};
 
/* Function to insert a node at the beginning */
static Node push( Node head_ref, int new_data)
{
    /* allocate node */
    Node new_node = new Node();
 
    /* put in the data */
    new_node.data = new_data;
 
    /* link the old list off the new node */
    new_node.next = (head_ref);
 
    /* move the head to point to the new node */
    (head_ref) = new_node;
     
    return head_ref;
}
 
/* Function to print linked list */
static void printList( Node head)
{
    Node temp = head;
    while (temp != null)
    {
        Console.Write("{0} ", temp.data);
        temp = temp.next;
    }
    Console.Write("\n");
}
 
// Function to skip M nodes and then
// delete N nodes of the linked list.
static void skipMdeleteN( Node head, int M, int N)
{
    Node curr = head, t;
    int count;
 
    // The main loop that traverses
    // through the whole list
    while (curr!=null)
    {
        // Skip M nodes
        for (count = 1; count < M &&
                curr != null; count++)
            curr = curr.next;
 
        // If we reached end of list, then return
        if (curr == null)
            return;
 
        // Start from next node and delete N nodes
        t = curr.next;
        for (count = 1; count <= N && t != null; count++)
        {
            Node temp = t;
            t = t.next;
        }
         
        // Link the previous list with remaining nodes
        curr.next = t;
 
        // Set current pointer for next iteration
        curr = t;
    }
}
 
// Driver code
public static void Main(String []args)
{
    /* Create following linked list
    1.2.3.4.5.6.7.8.9.10 */
    Node head = null;
    int M=2, N=3;
    head=push(head, 10);
    head=push(head, 9);
    head=push(head, 8);
    head=push(head, 7);
    head=push(head, 6);
    head=push(head, 5);
    head=push(head, 4);
    head=push(head, 3);
    head=push(head, 2);
    head=push(head, 1);
 
    Console.Write("M = {0}, N = {1} \nGiven" +
                        "Linked list is :\n", M, N);
    printList(head);
 
    skipMdeleteN(head, M, N);
 
    Console.Write("\nLinked list after deletion is :\n");
    printList(head);
}
}
 
// This code contributed by Rajput-Ji

Javascript




<script>
 
// Javascript program to delete N nodes
// after M nodes of a linked list
 
    // A linked list node
class Node {
    constructor() {
        this.data = 0;
        this.next = null;
    }
}
 
    /* Function to insert a node at the beginning */
    function push(head_ref , new_data) {
        /* allocate node */
var new_node = new Node();
 
        /* put in the data */
        new_node.data = new_data;
 
        /* link the old list off the new node */
        new_node.next = (head_ref);
 
        /* move the head to point to the new node */
        (head_ref) = new_node;
 
        return head_ref;
    }
 
    /* Function to print linked list */
    function printList(head) {
var temp = head;
        while (temp != null) {
            document.write(temp.data+" ");
            temp = temp.next;
        }
        document.write("<br/>");
    }
 
    // Function to skip M nodes and then
    // delete N nodes of the linked list.
    function skipMdeleteN(head , M , N) {
var curr = head, t;
        var count;
 
        // The main loop that traverses
        // through the whole list
        while (curr != null) {
            // Skip M nodes
            for (count = 1; count < M && curr != null;
            count++)
                curr = curr.next;
 
            // If we reached end of list, then return
            if (curr == null)
                return;
 
            // Start from next node and delete N nodes
            t = curr.next;
            for (count = 1; count <= N && t != null;
            count++)
            {
        var temp = t;
                t = t.next;
            }
 
            // Link the previous list with remaining nodes
            curr.next = t;
 
            // Set current pointer for next iteration
            curr = t;
        }
    }
 
    // Driver code
     
        /*
          Create following linked list
         1.2.3.4.5.6.7.8.9.10
         */
var head = null;
        var M = 2, N = 3;
        head = push(head, 10);
        head = push(head, 9);
        head = push(head, 8);
        head = push(head, 7);
        head = push(head, 6);
        head = push(head, 5);
        head = push(head, 4);
        head = push(head, 3);
        head = push(head, 2);
        head = push(head, 1);
 
        document.write(
        "M = "+M+", N = "+N+"<br/>Given Linked list is :<br/>"
        );
        printList(head);
 
        skipMdeleteN(head, M, N);
 
        document.write(
        "<br/>Linked list after deletion is :<br/>"
        );
        printList(head);
 
// This code contributed by gauravrajput1
 
</script>

Output: 



M = 2, N = 3
Given Linked list is :
1 2 3 4 5 6 7 8 9 10

Linked list after deletion is :
1 2 6 7

Time Complexity: O(n) where n is number of nodes in linked list. 
 

This article is contributed by Chandra Prakash. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above
 




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