Given a non-negative integer represented as a linked list of digits, plus one to the integer. The digits are stored such that the most significant digit is at the head of the list. Example 1: Input: head = [1,2,3] Output: [1,2,4] Example 2: Input: head = [0] Output: [1] Constraints: The number of nodes in the linked list is in the range [1, 100]. 0 <= Node.val <= 9 The number represented by the linked list does not contain leading zeros except for the zero itself.