Merge Two Sorted Lists

Problem

Given the heads of two sorted linked lists list1 and list2, merge the two lists into one sorted linked list. The new list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list.

Examples

mergeTwoLists([5, 10, 20, 30], [2, 8, 25, 35])
// [2, 5, 8, 10, 20, 25, 30, 35]

mergeTwoLists([100], [50, 75])
// [50, 75, 100]

mergeTwoLists([], [10, 20, 30, 40])
// [10, 20, 30, 40]