Javascript Program To Check Whether The Length Of Given Linked List Is Even Or Odd

Given a linked list, the task is to make a function which checks whether the length of the linked list is even or odd. Examples:

Input : 1->2->3->4->NULL
Output : Even

Input : 1->2->3->4->5->NULL
Output : Odd

Method 1: Count the codes linearly
Traverse the entire Linked List and keep counting the number of nodes. As soon as the loop is finished, we can check if the count is even or odd. You may try it yourself.
Method 2: Stepping 2 nodes at a time
Approach:

1. Take a pointer and move that pointer two nodes at a time
2. At the end, if the pointer is NULL then length is Even, else Odd.

Javascript

<script>
// JavaScript program to check length
// of a given linklist
// Defining structure
class Node
{
    constructor()
    {
        this.data = 0;
        this.next = null;
    }
}

// Function to check the length of
// linklist
function LinkedListLength(head)
{
    while (head != null &&
           head.next != null)
    {
        head = head.next.next;
    }
    if (head == null)
        return 0;
    return 1;
}

// Push function
function push(head, info)
{
    // Allocating node
    node = new Node();

    // Info into node
    node.data = info;

    // Next of new node to head
    node.next = (head);

    // head points to new node
    (head) = node;
}

// Driver code
head = null;

// Adding elements to Linked List
push(head, 4);
push(head, 5);
push(head, 7);
push(head, 2);
push(head, 9);
push(head, 6);
push(head, 1);
push(head, 2);
push(head, 0);
push(head, 5);
push(head, 5);
var check = LinkedListLength(head);

// Checking for length of linklist
if (check == 0)
{
    document.write("Odd");
}
else
{
    document.write("Even");
}
// This code is contributed by umadevi9616
</script>

Output:

Odd

Time Complexity: O(n) 
Auxiliary Space: O(1)

Using Recursion

Javascript

<script>
// JavaScript program to check length
// of a given linklist
// Defining structure
class Node
{
    constructor()
    {
        this.data = 0;
        this.next = null;
    }
}

// Recursive Function to check the length of
// linklist
function LinkedListLengthRecursive(head) {
    if (head == null) {
        return 0;
    }
    return 1 + LinkedListLengthRecursive(head.next);
}


// Push function
function push(head, info)
{
    // Allocating node
    node = new Node();

    // Info into node
    node.data = info;

    // Next of new node to head
    node.next = (head);

    // head points to new node
    (head) = node;
}

// Driver code
head = null;

// Adding elements to Linked List
push(head, 4);
push(head, 5);
push(head, 7);
push(head, 2);
push(head, 9);
push(head, 6);
push(head, 1);
push(head, 2);
push(head, 0);
push(head, 5);
push(head, 5);
var check = LinkedListLengthRecursive(head);

// Checking for length of linklist
if (check == 0)
{
    console.log("Odd");
}
else
{
    console.log("Even");
}
// This code is contributed by Vinay Pinjala.
</script>

Output

Odd

Time Complexity: O(n) 
Auxiliary Space: O(1)

Please refer complete article on Check whether the length of given linked list is Even or Odd for more details!