Anas_Da's blog

about cheating on last div 4
By Anas_Da, history, 5 months ago, In English

Hello codeforces

yesterday there was a div4

at the middle of the contest

I noticed that a large amount of coders came up with the solution of problem E at the same time

so (as I am unrated for div4 contest)

I did some search on internet

and found a live stream that is currently solving the problems

so I see the code of problem E

and I would say that it is very familiar to a lot of codes that get AC here at the time that it published

now a lot might say why would i care about div4

a lot of people waits div4 for positive delta

and I know coders that was getting around +100 rating

but because of that they got negative delta because they didn't come up with problem E

I will add some photos

youtube code
some codes from codeforces

my point is

cheating is bad for you

but if you don't care

just don't ruin contest for other people

  • Vote: I like it
  • +110
  • Vote: I do not like it

»
5 months ago, # |
← Rev. 2   Vote: I like it +16 Vote: I do not like it

Thanks Anas!!

This is really a serious issue

→ Reply
»
5 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Thank you very much; I couldn't solve problem E either. Still, I don't find much sense in 'hacking' the solution; you don't end up learning anything.

→ Reply
  • »
    »
    5 months ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    By hacking solutions one learns about how to come up with testcases which can break a solution and its a very important skill for both, problem creation and solving.

    → Reply
»
5 months ago, # |
← Rev. 2   Vote: I like it +15 Vote: I do not like it

not defending the cheaters, but the problem is pretty standard and the solution is obviously very likely to coincide so you $$$might've$$$ gotten the wrong people ? idk.

→ Reply
»
5 months ago, # |
  Vote: I like it +29 Vote: I do not like it

Such a beautiful poem.

Each line has a very profound meaning

I wish I could

Write a beautiful poem like this

→ Reply
»
5 months ago, # |
  Vote: I like it 0 Vote: I do not like it

It may get hacked later due to an unordered map ;)

→ Reply
  • »
    »
    5 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Can someone please explain why does the std::unordered_map gets hacked, but the std::map doesn't? Isn't the unordered one faster than the normal?

    → Reply
    • »
      »
      »
      5 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      unordered is linear at worst

      → Reply
    • »
      »
      »
      5 months ago, # ^ |
        Vote: I like it +1 Vote: I do not like it

      "collisions"

      → Reply
    • »
      »
      »
      5 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Unordered map uses hashing to store and retrieve elements, and a common problem in hashing is 'collisions' which will lead to complexity of O(n) in worst case for each operation done on the map while the normal map uses binary trees (Not sure), so the complexity will remain log(n) whatever values it has.

      → Reply
»
5 months ago, # |
  Vote: I like it -8 Vote: I do not like it

Thanks Anas_Da, people like you keeping people like us motivated by exposing cheating. In recent times rejudgement of previous rounds are great for me.

→ Reply
»
5 months ago, # |
  Vote: I like it +3 Vote: I do not like it

Oh, unordered map without safe hash, is there any blog on how to hack such unordered maps?

→ Reply
»
5 months ago, # |
← Rev. 2   Vote: I like it +12 Vote: I do not like it

This might explain the inf unordered_map hacks in the last div 4

→ Reply
»
5 months ago, # |
  Vote: I like it +15 Vote: I do not like it

last christmas, i gave you my code

but the very next day, you just got skipped

this year, to save me from -ve

i'll give it to someone with cheating skills

→ Reply
»
5 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I suggest not allowing people to comment on tha main blog of the contest during it, as they always hike people from there .

→ Reply
»
5 months ago, # |
  Vote: I like it +7 Vote: I do not like it

Thank you for trying to expose cheaters and I wish that Codeforces act soon so we can make this platform a better place for CP-ers

→ Reply
»
5 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I see that the solution uses an unordered map and according to my experience with unordered maps mostly there is a case that takes o(n) time rather than o(logn) so the solutions must've already been hacked by other coders. I don't think there is any reason to worry over the petty code codeforces will surely adjust the ratings after removing the cheaters.

→ Reply
»
5 months ago, # |
  Vote: I like it +5 Vote: I do not like it

They got the hacks they deserve.. I guess it was leaked on purpose to do more hacks. xD

→ Reply
»
5 months ago, # |
  Vote: I like it 0 Vote: I do not like it

https://codeforces.com/contest/1915/submission/239288878

I didnt watch the youtube video you are talking about and still have similar code to those you have refered to. The problem was just typical.

→ Reply