What is the need of the frequency array ? and why are we finding Mc2?

#1

why we care about 2 values in same bucket, why don’t we just find (b-a)%n==0 ?

#2

hello @premang
please check this video tutorial by prateek bhaiya->


here he has covered everthing
#3

this is the same video in cb i dont understand anything.

#4

see if we are getting same modulo in prefix sum i,e

…a . . . … … . . a …

then that means sum of elements between those two same modulo is divisible by n.
becuase then only
(a+something) %n = a%n
implies something%n=0

so let say we have
…a … a…a…a…
now here if i pick any two a then sum in between them will always be divisible by n.

so if p is the frequency of a in prefix sum array then p*(p-1)/2 such subarray will be there.

#5

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