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

You are given an array of unique integers salary where salary[i] is the salary of the ith employee.
Return the average salary of employees excluding the minimum and maximum salary. Answers within 10-5 of the actual answer will be accepted.
 
Please complete the following python code precisely:
```python
class Solution:
    def average(self, salary: List[int]) -> float:
```