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

Given an array of integers arr.
We want to select three indices i, j and k where (0 <= i < j <= k < arr.length).
Let's define a and b as follows:

a = arr[i] ^ arr[i + 1] ^ ... ^ arr[j - 1]
b = arr[j] ^ arr[j + 1] ^ ... ^ arr[k]

Note that ^ denotes the bitwise-xor operation.
Return the number of triplets (i, j and k) Where a == b.
 
Please complete the following python code precisely:
```python
class Solution:
    def countTriplets(self, arr: List[int]) -> int:
```