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

Given 2 integers n and start. Your task is return any permutation p of (0,1,2.....,2^n -1) such that :

p[0] = start
p[i] and p[i+1] differ by only one bit in their binary representation.
p[0] and p[2^n -1] must also differ by only one bit in their binary representation.

 
Please complete the following python code precisely:
```python
class Solution:
    def circularPermutation(self, n: int, start: int) -> List[int]:
```