Which data structure aids simplicity when deleting the nth node from the end of a singly linked list in one pass?

• A. A dummy tail node
• B. An auxiliary stack
• C. A dummy head node
• D. A sentinel at the end

Answer: (C)

Using a dummy head node gives a fixed predecessor for every node, including the head, so removing the nth node from the end can be done uniformly in one pass. You insert a dummy node before the real head and start two pointers at this dummy. Move one pointer forward by n+1 steps, then move both together until that pointer reaches the end. The other pointer will be right before the node to delete, so you can bypass the target with a simple pointer adjustment (slow.next = slow.next.next). This eliminates the need for a special case when the head itself is the node to delete, making the one-pass approach clean and straightforward. Other options don’t provide this consistent predecessor around the head, and using a stack would add extra space or remove the one-pass simplicity.