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

Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper, return the researcher's h-index.
According to the definition of h-index on Wikipedia: The h-index is defined as the maximum value of h such that the given researcher has published at least h papers that have each been cited at least h times.
 
Please complete the following python code precisely:
```python
class Solution:
    def hIndex(self, citations: List[int]) -> int:
```