Divisible subarray pigeon hole probelm

#1

i didnt understand how did the freq arr is converted into 3C2 + 2C2.
how did 3C2 ans 2C2 coming ??

#2

the number of times there is an occurence of a number , we take Nc2 of it

#3

why?? beacause in a prefix array whenever a number repeats say the number repeats at l, r then subarray from l to r-1 is a aaray which has 0 total sum%n, therefore we take. all subarrays of suck kind

#4

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