Divisible subarrays

#1

in this ques , why we put pre[0]=1 , while making the pre sum array

#2

because initially the sum is 0

can in case we encounter sum 0 then the count increases to 2.

if we are not putting pre[0] = 1 then we are not considering the case when initially the sum is 0

in that situation we are missing out on pairing of indexes which fetches us sum = 0

try working out for example i/p:
3 1 -3 -1

#3

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