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

We define a harmonious array as an array where the difference between its maximum value and its minimum value is exactly 1.
Given an integer array nums, return the length of its longest harmonious subsequence among all its possible subsequences.
 
Please complete the following python code precisely:
```python
class Solution:
    def findLHS(self, nums: List[int]) -> int:
```