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

Strings s1 and s2 are k-similar (for some non-negative integer k) if we can swap the positions of two letters in s1 exactly k times so that the resulting string equals s2.
Given two anagrams s1 and s2, return the smallest k for which s1 and s2 are k-similar.
 
Please complete the following python code precisely:
```python
class Solution:
    def kSimilarity(self, s1: str, s2: str) -> int:
```