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

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.
A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

 
Please complete the following python code precisely:
```python
class Solution:
    def letterCombinations(self, digits: str) -> List[str]:
```