Inserting a new node after a given node in a doubly linked list requires updating several pointers. Which option correctly performs this insertion after the given node?

• A. Set new.prev = NULL; new.next = node.next; if node.next != NULL, node.next.prev = new; node.next = new.
• B. Set new.next = node.prev; new.prev = node; node.prev.next = new; node = new.
• C. Set new.prev = node; new.next = NULL; node.next = new;
• D. Set new.prev = node; new.next = node.next; if node.next != NULL, node.next.prev = new; node.next = new.

Answer: (D)

The main idea is to maintain both forward and backward links when inserting after a node in a doubly linked list. To insert the new node right after the given node, you must connect the new node between the given node and the node that originally followed it. This means: new.prev should point to the given node, new.next should point to the original next node (node.next). If that original next node exists, its prev must be updated to the new node. Finally, the given node’s next should be updated to reference the new node. This sequence preserves the bidirectional connections for all involved nodes, including the edge case where the given node is the last node (in which case new.next is NULL and the conditional prevents dereferencing NULL).

That’s why the correct approach uses new.prev = node; new.next = node.next; if node.next != NULL, node.next.prev = new; node.next = new. The other options fail by misplacing the new node’s backward link, inserting in the wrong position, or breaking the backward/forward connections.