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

A stepping number is an integer such that all of its adjacent digits have an absolute difference of exactly 1.

For example, 321 is a stepping number while 421 is not.

Given two integers low and high, return a sorted list of all the stepping numbers in the inclusive range [low, high].
 
Please complete the following python code precisely:
```python
class Solution:
    def countSteppingNumbers(self, low: int, high: int) -> List[int]:
```