The test case input that is used to judge the submission is invalid and should be removed.
The description of the problem is as follows:
You are given two non-empty linked lists representing two non-negative integers.
Thats means that the input, as a whole, needs to resolve to an integer. After reversing input value 2 (because the linked lists represent the value in reverse order), your value is 9999999991. This is not an Integer in Java. Java Language Specification states that the maximum value for an integer is 2147483647. My solution is failing to submit due to this invalid case. This test case should be removed.