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ZCO · 2013 · Zonal Computing Olympiad · ZCO13003

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sorting · two-pointers · pair-counting

The organizer’s problem statement is available at the official source link.

threshold pairs

Count gum pairs below the limit

A valid pair has two distinct types whose hardness sum is strictly smaller than K.

sorted x_i <= x_jx_i + x_j < Kcount valid partner range
  1. 1

    Sort hardness

    Sort hardness values.
  2. 2

    Move two pointers

    For the smallest remaining value, move the right pointer until the sum is below K.
  3. 3

    Count valid pairs

    Count the valid partners, then advance the left boundary without double-counting pairs.
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