Reverse Linked List

Background

Linked list reversal is a fundamental pointer manipulation exercise appearing frequently in technical interviews.

Problem

Write a function that takes the head of a singly linked list and reverses it in place, returning the new head (previously the tail).

Input

The head node of a singly linked list, or null for an empty list.

Output

The new head node of the reversed linked list.

Sample tests

Input: 1 -> 2 -> 3 -> null

Expected: 3 -> 2 -> 1 -> null

Your solution

Learning objective

Master pointer manipulation in linked lists and understand in-place reversal techniques.