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#1

I am not getting How to use Fenwick tree Help

#2

@Bhawna hey ,use combinatorics and bit is teeling how many small numbers are there till that time which are inserted , so inserting and calculating together .

#3

I still didn’t understand

#4

@Bhawna hey in which section you are having problem?

#5

I am not getting from start,if possible plz explain step by step not just one line

#7

@Bhawna hey,
lets say we are considering a pair (x,y) of soldiers who communicate
assume x<y, so |x-y| = (y-x)
now we have 2 cases.
Case 1: b >= c
in this case the answer will simply be (y-x)*b, so total cost for this case is
sigma (y(i) - x) b
simplifying further, we get sigma (y) b - x b (number of soldiers having less bombs than current soldier)
To answer this one, we require 2 things:

  1. number of soldiers lying ahead having less bombs
  2. sum of their positions
    this can be answered with segment tree / fenwick tree.

Case 2: b < c
total cost for this case is
sigma [(y(i) - x) * c(i)]
simplifying:
sigma [y(i) c(i)] - sigma [x c(i)]
= sigma [y(i) c(i)] - x (sigma c(i) )
the first term can be found out by precomputing all y(i)*c(i) values, and proceeding in a similar way

#8

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