25. Reverse Nodes in k-Group

How to solve Reverse Nodes in k-Group (LeetCode 25): the approach in brief

The problem

Given the head of a linked list, reverse the nodes of the list k at a time, and return the modified list.

Pattern

Reverse Nodes in k-Group is a Linked List Manipulation Patterns problem, in the In-place Reversal subpattern. The pattern covers in-place reversal, merging sorted lists, reordering, and intersection detection

Master in-place linked list reversal including full reversal, partial reversal, and k-group reversal techniques.

Approach outline

1. Consider the problem as a series of smaller linked list segments of size k that need to be reversed individually.
2. Focus on how to traverse the linked list in chunks of k nodes and identify when you have enough nodes to reverse.
3. Think about reversing each k-sized segment in place by manipulating the next pointers without changing node values.

Complexity

The reference solution runs in O(n) time and O(1) space.

Asked at

Reverse Nodes in k-Group has been reported in interviews at Amazon, Microsoft, Apple, ByteDance, Facebook, Google.