In‐place reversal of LL - rFronteddu/general_wiki GitHub Wiki

Easy: Fundamentals & Prerequisites

These problems build the foundational muscle memory for rewiring pointers and traversing lists without using extra memory.

• Reverse Linked List Master doing this iteratively using three pointers (prev, curr, next) for O(1) space.
• Palindrome Linked List To solve this in O(1) space, you must find the middle and reverse the second half in-place before comparing.
• Middle of the Linked List The essential first step for any partial reversal problem (like palindromes or reordering). Teaches the fast/slow pointer technique.
• Merge Two Sorted Lists purely in-place.
• Intersection of Two Linked Lists

Medium: Sublists & Complex Rewiring

• Reverse Linked List II must reverse nodes strictly from position left to right while keeping the edges connected to the unreversed sections.
• Reorder List You have to find the middle (876), reverse the second half (206), and then interweave the two lists in-place.
• Swap Nodes in Pairs You are effectively reversing sublists of length 2 throughout the entire list.
• Maximum Twin Sum of a Linked List
• Odd Even Linked List You must carefully sever and reconnect alternating nodes into two separate lists, then merge them.
• Reverse Nodes in Even Length Groups
• Copy List with Random Pointer the optimal O(1) space solution is a masterclass in in-place manipulation—requiring you to weave cloned nodes into the original list and then carefully unweave them.

Hard: Advanced Manipulation

Hard linked list problems generally require you to maintain multiple overlapping pointers while performing repeating, complex sub-operations.

• Reverse Nodes in k-Group You must repeatedly reverse sublists of size k while perfectly maintaining the connecting edges for the previous and next groups.
• Merge k Sorted Lists Solving this optimally with Divide and Conquer requires merging lists completely in-place, testing your ability to manage pointers dynamically at scale.
• LFU Cache implementing this optimally requires building and manually wiring a complex 2D Doubly Linked List purely in-place, pushing your pointer tracking to the limit.