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

You are given a string allowed consisting of distinct characters and an array of strings words. A string is consistent if all characters in the string appear in the string allowed.
Return the number of consistent strings in the array words.
 
Please complete the following python code precisely:
```python
class Solution:
    def countConsistentStrings(self, allowed: str, words: List[str]) -> int:
```