Insert at Beginning of Circular Linked List in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a circular linked list?

A circular linked list is a linked list where the last node points back to the first node, forming a circle. There is no NULL at the end.

intermediate

Why do we need to update the last node when inserting at the beginning of a circular linked list?

Because the last node points to the first node, when we insert a new node at the beginning, the last node's next pointer must be updated to point to the new first node.

beginner

What happens if the circular linked list is empty and we insert a node at the beginning?

The new node points to itself, making it both the first and last node, forming a single-node circular linked list.

intermediate

Show the steps to insert a new node at the beginning of a non-empty circular linked list.

1. Create new node with data.<br>2. Find the last node (node whose next points to head).<br>3. Set new node's next to head.<br>4. Set last node's next to new node.<br>5. Update head to new node.

intermediate

What is the time complexity of inserting at the beginning of a circular linked list if we do not keep a tail pointer?

O(n), because we need to traverse the list to find the last node before updating its next pointer.

In a circular linked list, what does the last node's next pointer point to?

A The first node

B NULL

C Itself

D The second node

In a circular linked list, the last node points back to the first node to form a circle.

When inserting at the beginning of a circular linked list, which pointer must be updated besides the new node's next?

A The last node's next pointer

B The second node's next pointer

C The head pointer only

D No other pointer

The last node's next pointer must point to the new first node to maintain the circular structure.

If the circular linked list is empty, what should the new node's next pointer point to after insertion at beginning?

A NULL

B Itself

C Head

D Last node

For a single node circular linked list, the node points to itself.

What is the time complexity of inserting at the beginning of a circular linked list without a tail pointer?

A O(1)

B O(log n)

C O(n)

D O(n^2)

Finding the last node requires traversing the list, which takes O(n) time.

Which of the following is true about circular linked lists?

A They are the same as doubly linked lists

B They always have a NULL pointer at the end

C They cannot be empty

D They can be traversed starting from any node

Because the list is circular, you can start traversal from any node and visit all nodes.

Explain how to insert a new node at the beginning of a circular linked list and why updating the last node is necessary.

Think about the circular link from last node to first node.

Describe the difference in insertion steps when the circular linked list is empty versus when it has nodes.

Consider the special case of a single node.