Explain why a linked list is not suitable for random access by index in O(1), and what structure could provide fast random access.

• A. You must traverse from the head to reach an index, giving O(n); a dynamic array provides fast O(1) random access.
• B. Linked lists provide O(1) random access with a dedicated index; array is O(n).
• C. Linked lists provide O(log n) access; dynamic arrays are O(1).
• D. Random access is O(n) for both structures.

Answer: (A)

The main idea is how indexing time differs between linked lists and arrays. In a linked list, elements are linked one after another, so to reach a given index you must start at the head and traverse node by node until you reach that position. That makes index-based access take linear time, O(n). A dynamic array stores elements contiguously, so the element at a given index is directly addressable by combining the base address with the index offset, yielding O(1) random access. Therefore, the structure that provides fast random access is a dynamic array (or a regular array). If you need similar behavior with a linked-list-like structure, you’d have to add an auxiliary indexing structure, but the standard fast random access is provided by a dynamic array.