Identifying reversal subproblem

Some problems may consist of smaller subproblems that can be solved using the reversal technique. Solving these subproblems may either partially or fully solve the original problem. These are usually medium or hard problems, as breaking down a problem into subproblems may not be obvious and may require some critical observation. These problems are also implementation-heavy, meaning the solution code is often big and complex, which makes it error-prone.

Asking yourself the following questions will help you determine whether a problem is a reversal subproblem pattern problem or not.

Example

Let's consider an example problem and see how to break it down into smaller subproblems that can be solved using the reversal algorithm to understand it better.

Problem statement: Given a doubly linked list, reverse the list in groups of K in-place. If the last group in the list does not have K nodes, don't reverse it.