Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an integer array nums that does not contain any zeros, find the largest positive integer k such that -k also exists in the array.
Return the positive integer k. If there is no such integer, return -1.
 
Please complete the following python code precisely:
```python
class Solution:
    def findMaxK(self, nums: List[int]) -> int:
```