Reverse Singly Linked List

Problem

Given the head of a singly linked list, reverse the list in place and return the new head. Each node contains an integer value and a next pointer. If the list is empty, return None.

Constraints

• 0 <= n <= 5000, where n is the number of nodes
• -5000 <= Node.val <= 5000
• The list is singly linked
• The solution should run in linear time