Javascript Program To Delete Alternate Nodes Of A Linked List

Last Updated : 01 Sep, 2022

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.

Javascript

<script>
// Javascript program to delete alternate
// nodes of a linked list
 
// Head of list
var head; 
 
// 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 code
/* 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 is contributed by gauravrajput1 
</script>

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.

Auxiliary Space: O(1) because it is using constant space

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.

Javascript

<script>
/* Deletes alternate nodes of a list
   starting with head */
function deleteAlt(head) 
{ 
    if (head == null) 
        return; 
 
    var node = head.next; 
 
    if (node == null) 
        return; 
 
    // Change the next link of head    
    /* Recursively call for the new 
       next of head */
    head.next = node.next;    
    head.next = deleteAlt(head.next); 
} 
// This code contributed by aashish1995 
</script>