Let's discuss problems.

How to solve the geography problem?

Hey guys! Hello IOI 2018 contestants. How's everything at Japan?

Let's use this thread to get updates and discuss problems. Day 1 contest is a few hours away. Anyone who has a mirror link / live ranklist link please post in comments.

Hope everyone has a wonderful time!

We all have been waiting for this, a clean readable text version of Looking for a Challenge! My man Bar-B-Q informed me of it being finally out.

So without further adieu, here goes the link: https://www.nras.org.uk/data/events%20flyer%20front%20and%20back.pdf

Enjoy and leave a thanks for my man Bar-B-Q here. ^_^

Link: https://toph.co/p/breaking-math

The task is simple. Given n, k you gotta print

where ω(j) is the number of distinct prime factors of j.

Constraints: 1 ≤ k ≤ 10,  1 ≤ n ≤ 10¹¹.

TL is fuckin' big, 15 seconds. Wut do?

Problem: 351E - Jeff and Permutation

Abridged statement: given n ≤ 2000 integers, we can multiply some of them by  - 1. Goal is to minimize number of inversions (pairs (i, j) such that i < j and a_i > a_j). Print the minimum number of inversions.

Solution: 30244905

This solution replaces all numbers with its absolute value first. Then for each index i this solution adds min(L, R) to answer where L =  number of smaller elements to left, R =  number of smaller elements to right. Why does it work?

Why don't the IOI committee publish shortlisted problems and solutions like IMO does? It would be a great source of practice and countries could use the problems in their selection tests.