Singly Linked List – Get Length Operation

Get Length Operation in Singly Linked List

Calculating the number of nodes in a singly linked list.

To get the length of a singly linked list, we traverse the list from the head and count each node until we reach the end of the list (null).

This operation does not require random access or indexing; we simply move forward using the next pointers while incrementing a counter.

Visual Example

Suppose we have a singly linked list with the following values:

We want to calculate the length of the list by traversing it node by node and counting.

Step-by-Step Length Calculation

1. Start at the head node (value 5), count = 1.
2. Move to node with value 15, count = 2.
3. Move to node with value 25, count = 3.
4. Move to node with value 35, count = 4.
5. Move to node with value 45, count = 5.

We reach the end of the list. Total count = 5. This is the length of the singly linked list.

Complete Pseudocode: Get Length of Singly Linked List

This pseudocode shows how to calculate the length of a singly linked list by traversing it from start to end and counting the nodes.

function getLength(head):
    curr = head
    length = 0

    while curr != null:
        length += 1
        curr = curr.next

    return length

Let’s understand each part of the code step by step.

function getLength(head):
    curr = head
    length = 0

Explanation: We define the function and initialize two variables — curr to traverse the list and length to count nodes.

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    while curr != null:
        length += 1
        curr = curr.next

Explanation: We loop through the list, incrementing length for every node we visit and moving curr forward.

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    return length

Explanation: Once the loop finishes (i.e., we've visited every node), we return the total length of the list.

Singly Linked List Get Length Operation Examples

The following examples demonstrate how to calculate the length of a singly linked list.

Initial List	Length	Explanation
[10, 20, 30, 40, 50]	5	Start from the head and count each node until reaching null.
[5, 15, 25]	3	Three nodes are present in the list. Traverse and increment count by one for each.
[1]	1	Single node present. Length is 1.
[]	0	List is empty. Head is null, so the length is 0.

Time Complexity of Singly Linked List Get Length Operation

Length Calculation Case	Time Complexity	Explanation
Empty List	O(1)	We immediately check if the head is null and return 0.
Non-Empty List	O(n)	We traverse each node once from head to tail to count the total number of nodes.

Space Complexity of Singly Linked List Get Length Operation

Length Calculation	Space Complexity	Explanation
Get Length	O(1)	We use a single counter and a pointer variable to traverse the list. No additional space is required, regardless of the list size.

Key Takeaways

• The length of a singly linked list is calculated by traversing the list from head to tail.
• Each node is visited exactly once, making the operation linear in time.
• Only one pointer and one counter are needed, so space complexity remains constant.
• This operation does not modify the list structure — it’s a read-only traversal.
• Useful when the list does not maintain a length property and dynamic size checks are required.