Sunday, February 13, 2022

A global week

Codeforces Global Round 19 was the only round of this week (problems, results, top 5 on the left, analysis). tourist and Um_nik were pretty close, but Um_nik's two wrong attempts on E have set him back both in terms of points and in terms of contest time, so tourist came out on top. Congratulations!

Also well done to Maksim1744 for being the only other contestant to solve all problems. I have solved problem G at roughly the same time as him, but have more or less given up on solving H in the remaining time, while he persevered and was rewarded with the third place.

I think problem F, while a bit standard, was quite educational, so I encourage you to check it out as a good practice opportnity. However, since the last problem I described in this blog was also of this kind, let me instead focus on the very original problem G: you are given a single integer n. You start with a sequence of numbers 1, 2, 3, ..., n. In one step, you can take any two numbers x and y, and replace them with x+y and |x-y|. Your goal is to make all numbers equal, and you also need to make those equal final numbers as small as possible, and you need to do all this in at most 20n steps. Can you see a way? At least for me, it was quite helpful to experiment on a computer instead of just solving on paper.

Thanks for reading, and check back next week!


  1. maksim is my discord friend. Thank you. i am proud

  2. Great! Summarizes the CF Global 19 well. CP-Hall Of Fame ( has been a new one for me, hoping to get a listing there someday :)