Help with explanation

#1

prob: https://atcoder.jp/contests/abc194/tasks/abc194_c

Not able to understand the editorial please explain

#2

hello @raghav007

note following things
a) if we brute force the given formula then time complexity will be O(n^2) (a tle solutiom)
b) what forumla is doing ? it is just calculating square of all possible pairs right?
so if any number a occurs A times and a number b occurs B times in an array then what will be there overall contribution in the answer.
it will be (b-a) * (b-a) * A * B right?
so u have to do the same thing.
first prepare a frequency array and then use above formula among every possible pair to get ur answer.
c) Ai < = 200 that measn possible pairs will be less than 200 * 200
so this solutio will work

#3

ohh okay to come with this formula is there a specific thing I need to study or this too comes with practice

#4

with practice, and bit of pnc knowledge

#5

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