255's blog

By 255, history, 5 weeks ago, In English

Hello Codeforces, recently, there was a contest on CSAcademy named "FiiCode 2021 Round 2" and there was a task "Clown Fiesta", in a editorial for the task, there were lines such like:

If we take a sequence, where $$$a_0 = m$$$, $$$a_1 = \varphi (a_0)$$$, $$$a_2 = \varphi (a_1)$$$, $$$...$$$, $$$a_{k-1} = \varphi (a_{k-2}) \neq 1$$$, $$$a_k = \varphi (a_{k-1}) = 1$$$ and $$$m$$$ is prime number less than $$$10^9$$$, then $$$k$$$ will be not greater than $$$log_2(m)$$$.

Can someone prove it?

P.S. link to problem.

Read more »

 
 
 
 
  • Vote: I like it
  • +26
  • Vote: I do not like it

By 255, 4 months ago, In English

Hello, Codeforces. Today I solved problems in problemset and found interesting thing. Well known that when you create problems in polygon you can set custom output to tests in statements. It is used in many problems where you must output algorithm to solve. But, when you submit your code, you can see your output to test and jury's answer. The custom output on examples is used so that the participant does not understand the algorithm for solving by examples, but the jury's answers can lead the participant to the correct algorithm. For example, lets see second test from problem 1479C - Continuous City.

The output in statements:

Spoiler

The output in submission:

Spoiler

As we can see, outputs differ. I think this is serious bug, which can lead participants to jury's algorithm, and this should be fixed asap

Read more »

 
 
 
 
  • Vote: I like it
  • +94
  • Vote: I do not like it

By 255, history, 17 months ago, In English

MikeMirzayanov It's time to make year++ in CodeForces code :))

upd: it`s fixed now!

Read more »

 
 
 
 
  • Vote: I like it
  • +118
  • Vote: I do not like it