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

Given an array of integers arr, return true if and only if it is a valid mountain array.
Recall that arr is a mountain array if and only if:

arr.length >= 3
There exists some i with 0 < i < arr.length - 1 such that:
	
arr[0] < arr[1] < ... < arr[i - 1] < arr[i] 
arr[i] > arr[i + 1] > ... > arr[arr.length - 1]




 
Please complete the following python code precisely:
```python
class Solution:
    def validMountainArray(self, arr: List[int]) -> bool:
```