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How to Reverse a Sub-list Inside a Linked List

Learn how to efficiently reverse a sub-list within a linked list while maintaining the original head. This guide breaks down the solution step-by-step. --- This video is based on the question https://stackoverflow.com/q/73995595/ asked by the user 'Krellex' ( https://stackoverflow.com/u/14723580/ ) and on the answer https://stackoverflow.com/a/73996501/ provided by the user 'trincot' ( https://stackoverflow.com/u/5459839/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Reversing a sub-list inside a linked list and re-connecting original head Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Reversing a Sub-list Inside a Linked List: A Comprehensive Guide Working with linked lists can be tricky, especially when it comes to reversing a portion of it. In this post, we’ll explore how to reverse a sub-list within a linked list, focusing on keeping the original head intact. The Problem You might encounter issues when reversing a sub-list in larger linked lists. You might notice that while smaller lists (like those with just 2 elements) reverse seamlessly, larger ones tend to break down. This happens when you struggle to maintain connections to nodes outside the sub-list, leading to nullptr access errors. Example Scenarios Working Example: Input: [3, 5], left = 1, right = 2 Output: [5, 3] Failing Example: Input: [1, 2, 3, 4, 5], left = 2, right = 4 Output: [2, 4, 3, 2, 5] - clearly incorrect. Understanding how to connect nodes before and after the reversed section is key to solving this problem. The Solution Understanding the Code Below is the corrected version of the code to reverse a sub-list, followed by an explanation of the changes made for improvement. [[See Video to Reveal this Text or Code Snippet]] Key Improvements Using Dummy Nodes: The introduction of a dummy node allows for consistency in handling the head of the list when reversing. Maintaining Previous Node: By adjusting how prev is defined, we can ensure that it moves along with current, one step behind. This way, it can accurately point to the previous node of lastKnownParent. Efficient Connection Updates: Directly link the last known parent and the current node after reversing the sub-list. This ensures you aren’t hard-coding values that may not apply universally to any list configuration. Considerations for Robustness Input Validation: Check if the given left and right values lie within the bounds of the list. Edge Cases: Consider what should happen if right < left, or if the list is empty. Code Beautification: Break down functionality into smaller methods such as reversing the entire list or splitting the list into segments for better readability and maintenance. Conclusion Mastering the reversal of a sub-list in a linked list is a crucial skill in programming. By following the provided solution and improvements, you can effectively tackle linked list manipulations while ensuring the integrity of your data structure is maintained. Whether you're preparing for an interview or improving your coding skills, practice makes perfect. Happy coding!