Iterative List Reversal: When to Use It

Start with the idea

A problem is a good match for Iterative List Reversal when it asks for reverse traversal order and ownership-safe rewiring. Here the concrete task is: Return the node values after reversing the list. The visible input 1->2->3->4 is an example, not a definition of the whole problem. Ask what operations the solution must support and what the input guarantees. Look for tasks where node identity or one-way traversal matters. An indexed vector solution can hide the pointer constraint rather than solve it. The right choice follows from those guarantees, not from a familiar noun in the prompt.

The decisive invariant is: Detach the next link before redirecting the current node toward the reversed prefix. Try to say why it applies to the task without quoting the implementation. Which fact becomes known after one update, and which possible answers remain? A list algorithm changes relationships between nodes, not just values. Draw the next pointers before and after each mutation. If that claim cannot be maintained on a legal input, the pattern is wrong or one of its preconditions is missing. A counterexample is more useful than a vague warning: change one property of the sample, trace the first two steps, and identify the exact claim that fails.

Compare costs before committing. The advertised bound is O(n) time · O(1) links; identify the operation responsible for it and the extra memory it needs.