A 21st century week

Three  international events took place this week: the AWTF, the EGOI and the IMO. I have chosen the AWTF to attend in person (problems, results, top 5 on the left, mirror results, analysis in Japanese, broadcast recording). 6 out of 12 finalists were born in the 20th century, and the highest place the veterans have achieved was place 4. It feels a bit surreal that Andrew and Kevin are the veterans now. The podium places all went to the new generation from China — congratulations on the amazing performance! With rare exceptions, it took the contestants around 2 hours to solve B, C or D, if they could solve one of those at all. Zhou Kangyang, however, collected 2 of those exceptions by solving B and C very fast, and was the only contestant to solve D, so he was in the league of his own on the day.

I want to highlight problem B from the round: you are given n<=100 days and m movies, the i-th movie running from day l_i to day r_i (all pairs (l_i, r_i) are different). Find the sum of the following values: for each of the 2^m sets of movies, what is the maximum amount of different movies from that set one can watch, if one only watches at most one movie per day?

The 5th EGOI took place in Germany (problems and analysis, results, top 5 on the left). The scores were very close starting from place 4, but the first three places were separated quite visibly, even if the differences meant solving just a few more subtasks. Congratulations to Paulina, Anastasiia and Clara on the great results!

Problem C from the first day likely allowed many different approaches, including solving it fully on paper or by writing some helper programs: there are n<=50 players playing bingo. Each player will have a card with exactly 12 numbers, each between 1 and 50. Then, all numbers from 1 to 50 will be read out in some order, and the first player whose all 12 numbers have been read out will be declared the winner. Can you design the contents of the players' cards in such a way that there will never be a tie? This is essentially an output-only problem since there are only 50 fully independent test cases (n=1, n=2, ..., n=50). How many of those can you get? Bonus points if you can meaningfully use a computer to make progress.

The IMO 2025 (problems, results, top 5 on the left) is not typically within the scope of this blog, but there were two independent crossover points this time that made me bring it up. First, the skills required to solve IMO problems and the competitive programming problems (especially the AtCoder flavor), although not the same, are quite related, and strong competitors can often do both and move from one area to the other. Second, both areas are now at the forefront of the AI race, as they provide both nice datasets and objective evaluation opportunities for the general reasoning and general problem solving skills. It is unexpected and cool how what used to be a fun hobby now has the world's attention. Congratulations to the IMO 2025 participants who still hold their own against the AI, and I hope to meet some of you at the competitive programming events one day :)

Finally, Codeforces held Order Capital Round 1 to wrap up the week (problems, results, top 5 on the left, analysis). tourist has shown that the 20th century folk still stand a chance, and regained his first place in the overall ratings as a result. Well done, and thanks!

Thanks for reading, and check back next week.