Delete alternate nodes of a Linked List
Last Updated :
29 Apr, 2024
Given a Singly Linked List, starting from the second node delete all alternate nodes of it. For example, if the given linked list is 1->2->3->4->5 then your function should convert it to 1->3->5, and if the given linked list is 1->2->3->4 then convert it to 1->3.
Method 1 (Iterative)
Keep track of previous of the node to be deleted. First, change the next link of the previous node and iteratively move to the next node.
C++
// C++ program to remove alternate
// nodes of a linked list
#include <bits/stdc++.h>
using namespace std;
/* A linked list node */
class Node
{
public:
int data;
Node *next;
};
/* deletes alternate nodes
of a list starting with head */
void deleteAlt(Node *head)
{
if (head == NULL)
return;
/* Initialize prev and node to be deleted */
Node *prev = head;
Node *node = head->next;
while (prev != NULL && node != NULL)
{
/* Change next link of previous node */
prev->next = node->next;
delete(node); // delete the node
/* Update prev and node */
prev = prev->next;
if (prev != NULL)
node = prev->next;
}
}
/* UTILITY FUNCTIONS TO TEST fun1() and fun2() */
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
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 of the new node */
new_node->next = (*head_ref);
/* move the head to point to the new node */
(*head_ref) = new_node;
}
/* Function to print nodes in a given 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;
/* Using push() to construct below list
1->2->3->4->5 */
push(&head, 5);
push(&head, 4);
push(&head, 3);
push(&head, 2);
push(&head, 1);
cout<<"List before calling deleteAlt() \n";
printList(head);
deleteAlt(head);
cout<<"\nList after calling deleteAlt() \n";
printList(head);
return 0;
}
// This code is contributed by rathbhupendra
C
// C program to remove alternate nodes of a linked list
#include<stdio.h>
#include<stdlib.h>
/* A linked list node */
struct Node
{
int data;
struct Node *next;
};
/* deletes alternate nodes of a list starting with head */
void deleteAlt(struct Node *head)
{
if (head == NULL)
return;
/* Initialize prev and node to be deleted */
struct Node *prev = head;
struct Node *node = head->next;
while (prev != NULL && node != NULL)
{
/* Change next link of previous node */
prev->next = node->next;
/* Free memory */
free(node);
/* Update prev and node */
prev = prev->next;
if (prev != NULL)
node = prev->next;
}
}
/* UTILITY FUNCTIONS TO TEST fun1() and fun2() */
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
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 of the new node */
new_node->next = (*head_ref);
/* move the head to point to the new node */
(*head_ref) = new_node;
}
/* Function to print nodes in a given linked list */
void printList(struct Node *node)
{
while (node != NULL)
{
printf("%d ", node->data);
node = node->next;
}
}
/* Driver program to test above functions */
int main()
{
/* Start with the empty list */
struct Node* head = NULL;
/* Using push() to construct below list
1->2->3->4->5 */
push(&head, 5);
push(&head, 4);
push(&head, 3);
push(&head, 2);
push(&head, 1);
printf("\nList before calling deleteAlt() \n");
printList(head);
deleteAlt(head);
printf("\nList after calling deleteAlt() \n");
printList(head);
return 0;
}
Java
// Java program to delete alternate nodes of a linked list
class LinkedList {
Node head; // head of list
/* Linked list Node*/
class Node {
int data;
Node next;
Node(int d)
{
data = d;
next = null;
}
}
void deleteAlt()
{
if (head == null)
return;
Node node = head;
while (node != null && node.next != null) {
/* Change next link of next node */
node.next = node.next.next;
/*Update ref node to new alternate node */
node = node.next;
}
}
/* Utility functions */
/* Inserts a new Node at front of the list. */
public void push(int new_data)
{
/* 1 & 2: Allocate the Node &
Put in the data*/
Node new_node = new Node(new_data);
/* 3. Make next of new Node as head */
new_node.next = head;
/* 4. Move the head to point to new Node */
head = new_node;
}
/* Function to print linked list */
void printList()
{
Node temp = head;
while (temp != null) {
System.out.print(temp.data + " ");
temp = temp.next;
}
System.out.println();
}
/* Driver program to test above functions */
public static void main(String args[])
{
LinkedList llist = new LinkedList();
/* Constructed Linked List is 1->2->3->4->5->null */
llist.push(5);
llist.push(4);
llist.push(3);
llist.push(2);
llist.push(1);
System.out.println(
"Linked List before calling deleteAlt() ");
llist.printList();
llist.deleteAlt();
System.out.println(
"Linked List after calling deleteAlt() ");
llist.printList();
}
}
/* This code is contributed by Rajat Mishra */
Python3
# Python3 program to remove alternate
# nodes of a linked list
import math
# A linked list node
class Node:
def __init__(self, data):
self.data = data
self.next = None
# deletes alternate nodes
# of a list starting with head
def deleteAlt(head):
if (head == None):
return
# Initialize prev and node to be deleted
prev = head
now = head.next
while (prev != None and now != None):
# Change next link of previous node
prev.next = now.next
# Free memory
now = None
# Update prev and node
prev = prev.next
if (prev != None):
now = prev.next
# UTILITY FUNCTIONS TO TEST fun1() and fun2()
# Given a reference (pointer to pointer) to the head
# of a list and an , push a new node on the front
# of the list.
def push(head_ref, new_data):
# allocate node
new_node = Node(new_data)
# put in the data
new_node.data = new_data
# link the old list of 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 nodes in a given linked list
def printList(node):
while (node != None):
print(node.data, end = " ")
node = node.next
# Driver code
if __name__=='__main__':
# Start with the empty list
head = None
# Using head=push() to construct below list
# 1.2.3.4.5
head = push(head, 5)
head = push(head, 4)
head = push(head, 3)
head = push(head, 2)
head = push(head, 1)
print("List before calling deleteAlt() ")
printList(head)
deleteAlt(head)
print("\nList after calling deleteAlt() ")
printList(head)
# This code is contributed by Srathore
C#
// C# program to delete alternate
// nodes of a linked list
using System;
public class LinkedList
{
Node head; // head of list
/* Linked list Node*/
public class Node
{
public int data;
public Node next;
public Node(int d)
{
data = d; next = null;
}
}
void deleteAlt()
{
if (head == null)
return;
Node prev = head;
Node now = head.next;
while (prev != null && now != null)
{
/* Change next link of previous node */
prev.next = now.next;
/* Free node */
now = null;
/*Update prev and now */
prev = prev.next;
if (prev != null)
now = prev.next;
}
}
/* Utility functions */
/* Inserts a new Node at front of the list. */
public void push(int new_data)
{
/* 1 & 2: Allocate the Node &
Put in the data*/
Node new_node = new Node(new_data);
/* 3. Make next of new Node as head */
new_node.next = head;
/* 4. Move the head to point to new Node */
head = new_node;
}
/* Function to print linked list */
void printList()
{
Node temp = head;
while(temp != null)
{
Console.Write(temp.data+" ");
temp = temp.next;
}
Console.WriteLine();
}
/* Driver code*/
public static void Main(String []args)
{
LinkedList llist = new LinkedList();
/* Constructed Linked List is
1->2->3->4->5->null */
llist.push(5);
llist.push(4);
llist.push(3);
llist.push(2);
llist.push(1);
Console.WriteLine("Linked List before" +
"calling deleteAlt() ");
llist.printList();
llist.deleteAlt();
Console.WriteLine("Linked List after" +
"calling deleteAlt() ");
llist.printList();
}
}
// This code has been contributed
// by 29AjayKumar
JavaScript
<script>
// Javascript program to delete alternate
// nodes of a linked list
var head; // head of list
/* Linked list Node */
class Node {
constructor(val) {
this.data = val;
this.next = null;
}
}
function deleteAlt() {
if (head == null)
return;
var prev = head;
var now = head.next;
while (prev != null && now != null) {
/* Change next link of previous node */
prev.next = now.next;
/* Free node */
now = null;
/* Update prev and now */
prev = prev.next;
if (prev != null)
now = prev.next;
}
}
/* Utility functions */
/* Inserts a new Node at front of the list. */
function push(new_data) {
/*
* 1 & 2: Allocate the Node & Put in the data
*/
var new_node = new Node(new_data);
/* 3. Make next of new Node as head */
new_node.next = head;
/* 4. Move the head to point to new Node */
head = new_node;
}
/* Function to print linked list */
function printList() {
var temp = head;
while (temp != null) {
document.write(temp.data + " ");
temp = temp.next;
}
document.write("<br/>");
}
/* Driver program to test above functions */
/* Constructed Linked List is
1->2->3->4->5->null */
push(5);
push(4);
push(3);
push(2);
push(1);
document.write(
"Linked List before calling deleteAlt() <br/>"
);
printList();
deleteAlt();
document.write(
"Linked List after calling deleteAlt()<br/> "
);
printList();
// This code contributed by gauravrajput1
</script>
OutputList before calling deleteAlt()
1 2 3 4 5
List after calling deleteAlt()
1 3 5
Time Complexity: O(n)
where n is the number of nodes in the given Linked List.
Auxiliary Space: O(1)
As constant extra space is used.
Method 2 (Recursive)
Recursive code uses the same approach as method 1. The recursive code is simple and short but causes O(n) recursive function calls for a linked list of size n.
C++
#include <iostream>
using namespace std;
// Define a structure for the linked list node
struct Node {
int data;
Node* next;
Node(int value) : data(value), next(nullptr) {}
};
// Function to delete alternate nodes using recursion
void deleteAlt(Node* node) {
if (node == nullptr || node->next == nullptr) {
return;
}
Node* temp = node->next;
node->next = temp->next;
delete temp;
deleteAlt(node->next);
}
// Function to print the linked list
void printList(Node* head) {
while (head != nullptr) {
cout << head->data << " ";
head = head->next;
}
cout << endl;
}
int main() {
// Create the linked list with the given input: 1, 2, 3, 4, 5
Node* head = new Node(1);
head->next = new Node(2);
head->next->next = new Node(3);
head->next->next->next = new Node(4);
head->next->next->next->next = new Node(5);
cout << "Original linked list: ";
printList(head);
// Call the function to delete alternate nodes
deleteAlt(head);
cout << "Modified linked list after deleting alternate nodes: ";
printList(head);
// Free memory
Node* current = head;
while (current != nullptr) {
Node* next = current->next;
delete current;
current = next;
}
return 0;
}
C
#include <stdio.h>
#include <stdlib.h>
// Define a structure for the linked list node
struct Node {
int data;
struct Node* next;
};
// Function to delete alternate nodes using recursion
void deleteAlt(struct Node* node) {
if (node == NULL || node->next == NULL) {
return;
}
struct Node* temp = node->next;
node->next = temp->next;
free(temp);
deleteAlt(node->next);
}
// Function to print the linked list
void printList(struct Node* head) {
while (head != NULL) {
printf("%d ", head->data);
head = head->next;
}
printf("\n");
}
int main() {
// Create the linked list with the given input: 1, 2, 3, 4, 5
struct Node* head = (struct Node*)malloc(sizeof(struct Node));
head->data = 1;
head->next = (struct Node*)malloc(sizeof(struct Node));
head->next->data = 2;
head->next->next = (struct Node*)malloc(sizeof(struct Node));
head->next->next->data = 3;
head->next->next->next = (struct Node*)malloc(sizeof(struct Node));
head->next->next->next->data = 4;
head->next->next->next->next = (struct Node*)malloc(sizeof(struct Node));
head->next->next->next->next->data = 5;
head->next->next->next->next->next = NULL;
printf("Original linked list: ");
printList(head);
// Call the function to delete alternate nodes
deleteAlt(head);
printf("Modified linked list after deleting alternate nodes: ");
printList(head);
// Free memory
struct Node* current = head;
while (current != NULL) {
struct Node* next = current->next;
free(current);
current = next;
}
return 0;
}
Java
class LinkedList {
static class Node {
int data;
Node next;
Node(int value) {
data = value;
next = null;
}
}
// Function to delete alternate nodes using recursion
static void deleteAlt(Node node) {
if (node == null || node.next == null) {
return;
}
Node temp = node.next;
node.next = temp.next;
temp = null;
deleteAlt(node.next);
}
// Function to print the linked list
static void printList(Node head) {
while (head != null) {
System.out.print(head.data + " ");
head = head.next;
}
System.out.println();
}
public static void main(String[] args) {
// Create the linked list with the given input: 1, 2, 3, 4, 5
Node head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);
head.next.next.next = new Node(4);
head.next.next.next.next = new Node(5);
System.out.print("Original linked list: ");
printList(head);
// Call the function to delete alternate nodes
deleteAlt(head);
System.out.print("Modified linked list after deleting alternate nodes: ");
printList(head);
}
}
Python3
class Node:
def __init__(self, value):
self.data = value
self.next = None
# Function to delete alternate nodes using recursion
def delete_Alt(node):
if node is None or node.next is None:
return
temp = node.next
node.next = temp.next
temp = None
delete_Alt(node.next)
# Function to print the linked list
def print_list(head):
while head:
print(head.data, end=" ")
head = head.next
print()
# Create the linked list with the given input: 1, 2, 3, 4, 5
head = Node(1)
head.next = Node(2)
head.next.next = Node(3)
head.next.next.next = Node(4)
head.next.next.next.next = Node(5)
print("Original linked list:", end=" ")
print_list(head)
# Call the function to delete alternate nodes
delete_Alt(head)
print("Modified linked list after deleting alternate nodes:", end=" ")
print_list(head)
C#
using System;
class LinkedList {
class Node {
public int Data;
public Node Next;
public Node(int value) {
Data = value;
Next = null;
}
}
// Function to delete alternate nodes using recursion
static void DeleteAlt(Node node) {
if (node == null || node.Next == null) {
return;
}
Node temp = node.Next;
node.Next = temp.Next;
temp = null;
DeleteAlt(node.Next);
}
// Function to print the linked list
static void PrintList(Node head) {
while (head != null) {
Console.Write(head.Data + " ");
head = head.Next;
}
Console.WriteLine();
}
static void Main(string[] args) {
// Create the linked list with the given input: 1, 2, 3, 4, 5
Node head = new Node(1);
head.Next = new Node(2);
head.Next.Next = new Node(3);
head.Next.Next.Next = new Node(4);
head.Next.Next.Next.Next = new Node(5);
Console.Write("Original linked list: ");
PrintList(head);
// Call the function to delete alternate nodes
DeleteAlt(head);
Console.Write("Modified linked list after deleting alternate nodes: ");
PrintList(head);
}
}
JavaScript
class Node {
constructor(value) {
this.data = value;
this.next = null;
}
}
// Function to delete alternate nodes using recursion
function deleteAlt(node) {
if (node === null || node.next === null) {
return;
}
let temp = node.next;
node.next = temp.next;
temp = null;
deleteAlt(node.next);
}
// Function to print the linked list
function printList(head) {
let current = head;
while (current !== null) {
process.stdout.write(current.data + " ");
current = current.next;
}
console.log();
}
// Create the linked list with the given input: 1, 2, 3, 4, 5
let head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);
head.next.next.next = new Node(4);
head.next.next.next.next = new Node(5);
process.stdout.write("Original linked list: ");
printList(head);
// Call the function to delete alternate nodes
deleteAlt(head);
process.stdout.write("Modified linked list after deleting: ");
printList(head);
OutputOriginal linked list: 1 2 3 4 5
Modified linked list after deleting alternate nodes: 1 3 5
Time Complexity: O(n)
Auxiliary Space: O(1)
As this is a tail recursive function no function call stack is required thus the extra space used is constant.
Please write comments if you find the above code/algorithm incorrect, or find better ways to solve the same problem.
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