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Java Program To Delete Alternate Nodes Of A Linked List

  • Last Updated : 16 Dec, 2021

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.

Java




// Java program to delete alternate 
// nodes of a linked list
class LinkedList
{
    // Head of list
    Node head;  
   
    // Linked list Node
    class Node
    {
        int data;
        Node next;
        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)
        {
           System.out.print(temp.data + " ");
           temp = temp.next;
        }  
        System.out.println();
    }
  
     // 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);
          
        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 

Output: 

List 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.

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.

Java




/* Deletes alternate nodes of 
   a list starting with head */
static Node deleteAlt(Node head) 
    if (head == null
        return
  
    Node node = head.next; 
  
    if (node == null
        return
  
    // Change the next link of head 
    head.next = node.next; 
  
  
    /* Recursively call for the new 
       next of head */
    head.next = deleteAlt(head.next); 
// This code is contributed by Arnab Kundu

Time Complexity: O(n)

Please refer complete article on Delete alternate nodes of a Linked List for more details!


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