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

You are given an integer array nums and an integer target.
You want to build an expression out of nums by adding one of the symbols '+' and '-' before each integer in nums and then concatenate all the integers.

For example, if nums = [2, 1], you can add a '+' before 2 and a '-' before 1 and concatenate them to build the expression "+2-1".

Return the number of different expressions that you can build, which evaluates to target.
 
Please complete the following python code precisely:
```python
class Solution:
    def findTargetSumWays(self, nums: List[int], target: int) -> int:
```