Saturday, July 28, 2018

A too simple week

The Jun 18 - Jun 24 week had Codeforces Round 492 (problems, results, top 5 on the left, analysis). I've also included myself in the standings on the left to highlight the fact that OO0OOO00O0OOO0O00OOO0OO's performance was so amazing that he got all 6 problems accepted before I got any one of those :) Well done!

Right after this round, Scott Wu and Andrew He streamed a post-contest discussion on twitch (CF post). Unfortunately the recording is no longer available, but the concept is exciting and I've enjoyed listening to a part of it.

The round had a few mathy problems, but I'd like to highlight problem E which had a more algorithmic flavor: you are given a prime modulo p up to 109 and two numbers u and v between 0 and p-1. In one step, you can either add one modulo p, subtract one modulo p, or take inverse modulo p. You need to obtain v from u in at most 200 steps (the solution doesn't need to be the shortest). Do you see a way?

Thanks for reading, and check back for more!


  1. That's cool that you got a high place even though you only submitted the first problem so late...

    I tried going over your solution for E and was unable to understand it. Looking forward to you explaining it :)

  2. Hi. I updated my analysis of SRM ratings per the feedback received. if you'd like to look again.
    Thanks for the helpful comments.