Count the most common occurrence of subarray sum.

Constraints:

N <= 1e6; abs(ai) <= 1e6

Ex:

Inp:

5

1 1 2 1 4

Out:

3 (there are 3 subarray with the sum of 4: (1, 1, 2), (1, 2, 1), (4)

This question appears in ones of my friends competition and I have no idea how to solve it. Can someone help? Thanks.