What are common pitfalls when deleting nodes in a doubly linked list?

• A. Forgetting to update both next and prev; not adjusting head and tail; memory leaks.
• B. Only updating next pointers.
• C. Always deleting the head.
• D. Never updating pointers when deleting tail.

Answer: (D)

Deleting a node in a doubly linked list hinges on reconnecting its neighbors correctly and updating the list’s endpoints. The key is to change the neighboring links so the list remains intact in both directions: the previous node’s next should skip over the deleted node and point to its next, while the next node’s prev should point back to the deleted node’s previous. This ensures traversal in either direction stays consistent after the removal.

Edge cases require special care. If you’re removing the head, move the head pointer to the next node and set that node’s prev to null. If you’re removing the tail, move the tail pointer to the previous node and set its next to null. If the list becomes empty, both head and tail must be null. Don’t forget to free the memory of the deleted node to avoid leaks.

Common pitfalls stem from forgetting one of these updates. Updating only the next pointers while neglecting the prev links can leave dangling references and break backward traversal. Failing to adjust head or tail when removing end nodes can disconnect parts of the list or leave invalid endpoints. Handling all cases together—mid-list deletions, head deletions, tail deletions, and single-element lists—keeps the structure valid and prevents subtle bugs.