You are given the heads of two sorted linked lists, list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list.

Given the head of a singly linked list, our task is to reverse the list and return the reversed version. For example, if the input linked list is [1, 2, 3, 4, 5], the reversed list should be [5, 4, 3, 2, 1].