# 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.
