In an array A of 0s and 1s, how many non-empty subarrays have sum S?
Example 1:
Input: A = [1,0,1,0,1], S = 2
Output: 4
Explanation:
The 4 subarrays are bolded below:
[1,0,1,0,1]
[1,0,1,0,1]
[1,0,1,0,1]
[1,0,1,0,1]
Note:
A.length <= 30000
0 <= S <= A.length
A[i] is either 0 or 1.