Which one of the following statements is TRUE about the time complexity of algorithms that solve the above problem in $O(1)$ space?

A singly linked list with $n$ nodes can be reversed in-place using three pointers (prev, curr, next) in $O(1)$ auxiliary space.

In this iterative algorithm:

• We iterate through each node once from head to tail.

• At each step, the next pointer of the current node is reversed to point to prev.

• A total of $n$ nodes are visited and processed in constant time per node.

Thus, the algorithm runs in $\Theta(n)$ (or $\theta(n)$) time in the worst case using $O(1)$ space. Since every node's pointer must be modified, $\Omega(n)$ is also the lower bound, making $\theta(n)$ the best possible time complexity.

Therefore, option A is the correct statement.