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

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Every close bracket has a corresponding open bracket of the same type.

 
Please complete the following python code precisely:
```python
class Solution:
    def isValid(self, s: str) -> bool:
```