Delete alternate nodes of a Linked List in JAVA
JAVA Program to Delete Alternate Nodes of a Singly Linked List
In this page we’ll take a look at a JAVA program in which we’ll delete alternate nodes in a singly Linked List starting fro the second node of the list. We’ll simply have to just change the address stored in the element before the element that is to be deleted and change it to the address of the element that is after the element, to be deleted.
Algorithm
The basic idea is that we keep track of previous of the node to be deleted and change its next link.
- Take two pointers- nm1 and n. nm1 represents the previous of the node to be deleted. n represents the actual node to be deleted.
- Inialize nm1 with head and the nth node with next of the head.
- While nm1 and n are not null, change the next link of previous node (nm1) to next of the node n. Update nm1 with the next of nth node. Also update the nth node if nm1 is not null.
- With the end of while loop in step 4, all alternate nodes would be deleted.
Code in JAVA Programming Language to Delete Alternate Nodes from a Linked List
Run
import java.util.*;
class LinkedList
{
private class Node
{
int data;
Node next;
// Node constructor
// There are two fields in the node- data and address of next node
public Node (int data, Node next)
{
this.data = data;
this.next = next;
}
}
private Node head;
private Node tail;
private int size;
// Linked list constructor
public LinkedList ()
{
this.head = null;
this.tail = null;
this.size = 0;
}
// Function to find the size of linked list
public int size ()
{
return this.size;
}
// Function to check whether linked list is empty or not
public boolean isEmpty ()
{
return this.size () == 0;
}
// Function to traverse and print the linked list
public void display ()
{
Node temp = head;
while (temp != null)
{
System.out.print (temp.data + "-->");
// Set temp to point to the next node
temp = temp.next;
}
System.out.println ("END");
}
// Function to add a node in beginning of linked list
public void addFirst (int item)
{
// Create a temp node which points to head
Node temp = new Node (item, head);
// If linked list is empty, temp is the head and tail node both
if (this.size == 0)
{
this.head = this.tail = temp;
}
// else set the head such that it now points to temp node
else
{
this.head = temp;
}
this.size++;
}
public void deleteAlternateNodes ()
{
this.deleteAlternateNodes (this.head);
}
//Function to delete alternate nodes in linked list
private void deleteAlternateNodes (Node node)
{
//Base case
if (node == null)
{
return;
}
Node nm1 = this.head;
Node n = nm1.next;
while (nm1 != null && n != null)
{
nm1.next = n.next;
nm1 = n.next;
if (nm1 != null)
{
n = nm1.next;
}
}
}
}
public class Main
{
public static void main (String[]args) throws Exception
{
LinkedList ll = new LinkedList ();
ll.addFirst (70);
ll.addFirst (60);
ll.addFirst (50);
ll.addFirst (40);
ll.addFirst (30);
ll.addFirst (20);
ll.addFirst (10);
ll.display ();
ll.deleteAlternateNodes ();
ll.display ();
}
}
10-->20-->30-->40-->50-->60-->70-->END 10-->30-->50-->70-->END
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public void deletealternate(){
node pre=head;
int size=size();
if(size==0){
System.out.println(“invalid deletion”);
}
if(size%2!=0){
while(pre.next!=null){
pre.next=pre.next.next;
pre=pre.next;
}
}
else{
while(pre!=null){
pre.next=pre.next.next;
pre=pre.next;
}
}
}