What is the purpose of the swap() method in the LList class?

• A. It sorts the elements.
• B. It exchanges the contents of two lists efficiently.
• C. It appends one list to another.
• D. It reverses the order of elements.

Answer: (B)

The main idea being tested is exchanging entire list contents without moving each element. In a linked list, what defines a list is the reference to its first node (the head) and, often, other state like the tail pointer or size. The swap operation accomplishes this by swapping those references between two LList objects, so each list ends up pointing to the other’s sequence of nodes. This happens in constant time because you’re just reassigning pointers, not re-linking or moving every node.

For example, if one list contains 1 → 2 → 3 and another contains 4 → 5, after the swap the first list will contain 4 → 5 and the second will contain 1 → 2 → 3, with no node data touched. If the class keeps extra state such as tail or size, those should be swapped as well to keep internal consistency.

This operation differs from sorting (which rearranges elements), appending (which joins lists end-to-start), or reversing (which changes the order of the existing links).