Merge Two Sorted Lists

You are given the heads of two sorted linked lists list1 and list2. Merge them into one sorted linked list by splicing together the nodes of the two lists, and return the head of the merged list.

Example 1:

Input: list1 = [1,2,4], list2 = [1,3,4]
Output: [1,1,2,3,4,4]

Example 2:

Input: list1 = [], list2 = []
Output: []

Example 3:

Input: list1 = [], list2 = [0]
Output: [0]

Constraints:

• The number of nodes in both lists is in the range [0, 50]
• -100 ≤ Node.val ≤ 100
• Both list1 and list2 are sorted in non-decreasing order