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

Given two strings a and b, return the length of the longest uncommon subsequence between a and b. If no such uncommon subsequence exists, return -1.
An uncommon subsequence between two strings is a string that is a subsequence of exactly one of them.
 
Please complete the following python code precisely:
```python
class Solution:
    def findLUSlength(self, a: str, b: str) -> int:
```