Given an array of integer nums, and NO TARGET SUM GIVEN
find the number of subArray that sums to the same target

for e.g nums = [1,9,8 10, 2]

[1,9] and [8,2] adds to the same sum. return the count
ans: 2
Explanation: Both (1 and 9), (8 and 2) adds to 10. 

Constraints: 
The subarray must be unique, ie, you cannot have one element in both subarrays.
The subarray must contain only 2 elements

Another e.g [3,3,3,9] 
ans = 1. [3,3] sum up to 6.

[3,3] [3,3] would be invalid. There can't be duplicates of 3 in both sub arrays