Merge Sorted Linked Lists

Given the heads of two sorted linked lists, merge them into one sorted linked list and return the head of the merged list.

The merged list must preserve sorted order and should reuse the existing nodes rather than creating a separate sorted array.

Examples
Input: [[1,2,4],[1,3,4]]
Output: [1,1,2,3,4,4]
Hints
Related Problems

Merge Sorted Linked Lists

Given the heads of two sorted linked lists, merge them into one sorted linked list and return the head of the merged list.