Rating changes for the last round are temporarily rolled back. They will be returned soon. ×

djm03178's blog

By djm03178, history, 6 weeks ago, In English,

1304A — Two Rabbits

Tutorial
Solution

1304B — Longest Palindrome

Tutorial
Solution

1304C — Air Conditioner

Tutorial
Solution

1304D — Shortest and Longest LIS

Tutorial
Solution

1304E — 1-Trees and Queries

Tutorial
Solution

1304F1 — Animal Observation (easy version)

Tutorial
Solution

1304F2 — Animal Observation (hard version)

Tutorial
Solution: O(nmlogm)
Solution: O(nm)

Read more »

 
 
 
 
  • Vote: I like it
  • +205
  • Vote: I do not like it

By djm03178, history, 6 weeks ago, In English,

안녕하세요, 코드포스! (Hello, Codeforces!)

I'm glad to invite you to Codeforces Round #620 (Div. 2). The contest will start at 15.02.2020 16:05 (Московское время), and it is rated for all participants with ratings under 2100.

You will be given 6 problems and one of the problems has 2 subtasks. The contest duration is 2 hours. The score distribution will be announced later.

All problems are prepared by me, with huge help from the testers with developing great solutions.

I'll be on the community Discord server after the contest to share my thoughts and get feedback about the problems.

Thanks to 79brue, molamola., FlowerOfSorrow, evenharder, cs71107, Justice_Hui, rkm0959, chpark1111, imeimi, alswhp, gaelim, jh05013 (Good tester), yuto0518, N_jara, aryanc403, SnowGoose, --Someone--, surung9898, and ko_osaga for testing the round. I would also like to thank 300iq for round coordination, and MikeMirzayanov for the great Codeforces and Polygon system.

Hope you enjoy the problems!

UPD: The scoring distribution is 500 — 1000 — 1500 — 1750 — 2000 — (2000 + 1000)

UPD2: The contest is finished! Thanks so much for your participation! The editorial is here.

UPD3: Congratulations to the winners!

Div. 2

1: ltst

2: COVID-19

3: cosplay

4: sincerity

5: ChitandaEru

Unofficial Div. 1

1: wucstdio

2: ksun48

3: jiangly

4: uwi

5: teapotd

Read more »

 
 
 
 
  • Vote: I like it
  • +530
  • Vote: I do not like it

By djm03178, history, 8 months ago, In English,

The problems with Gildong (B, D, F) are by me, and Amugae (A, C, E) are by hyunuk.

Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...

Read more »

 
 
 
 
  • Vote: I like it
  • +157
  • Vote: I do not like it

By djm03178, 8 months ago, In English,

안녕하세요, 코드포스! (Hello, Codeforces!)

We're glad to introduce you to Codeforces Round #578 (Div. 2), which will start at Aug/11/2019 15:35 (Moscow time). The round is rated for Div. 2 participants.

You will be given 6 problems and 2 hours to solve them. The score distribution will be announced later.

The problems are prepared by hyunuk and me.

Thanks to pllk, Learner99, Rox, mohammedehab2002, cheetose, jh05013, rkm0959, edenooo, and alex9801 for testing the round. We would also like to specially thank to KAN and arsijo for coordinating the round, and of course, MikeMirzayanov for Codeforces and Polygon platform.

This is our very first round, so I hope you enjoy it a lot!

UPD: The scoring distribution is 500 — 1000 — 1250 — 2000 — 2000 — 2500

UPD2: The contest is finished. Thanks for joining us! Here's the editorial.

UPD3: Congratulations to the winners!

Div. 2

1: gamegamewillwinioi2020

2: oliviahye

3: ccf_n0i

4: 2om_neek

5: Tropical_maid

Unofficial Div. 1

1: kcm1700

2: uwi

3: square1001

4: kmjp

5: KrK

Read more »

 
 
 
 
  • Vote: I like it
  • +583
  • Vote: I do not like it

By djm03178, 15 months ago, In English,

Currently, any successful hacks on any problem provide exactly 100 points. For problem A and B it seems quite reasonable, but I find it barely motivating to lock harder problems and try to hack (unless it's known that the pretests are exceptionally weak), since:

  • You risk losing a lot of points on system test. Even if you realize mistakes in your code after lock, you can't do anything.
  • There are (usually) not many solutions to look into in your room in the first place.
  • Harder problems (usually) require hard techniques and longer implementation, so reading each solution takes a lot of time.
  • Even if you successfully hack, 100 points don't affect your rank too much.

Rewarding more points for hacking solutions for harder problems would make the system more interesting and balanced. My suggestion is to reward 1/10 of the problem's score for successful hacks. i.e. 50 points for hacking a solution of a 500-point problem, and 200 points for hacking a 2000-point problem.

Here are some reasons for the suggestion:

  • Hacking solutions of a hard problem requires you to understand the hard problem itself, high-level logic behind the codes, and complicated implementations.
  • There are usually more pretests on harder problems, so the chance of passing all pretests on harder problems with a wrong solution is already low.
  • Currently hacks are mostly only for easier problems. If people would be motivated to lock harder problems too, that would make the use of hacks more balanced.
  • It may seem that 300 points for hacking one solution is too much. But this implies that the contestant has solved (or at least, passed pretests) a 3000-point problem. For example in Codeforces Round #509 (Div. 2), if you solved all problems and have 7700 points, you would be at rank 33. Even if you successfully hack a solution on F, you would be only at rank 25. On the other hand, if you solved problem A only and have 450 points, then you hack a solution on A, your rank will be: 4410 -> 4062.
  • For easier problems you usually read a lot of solutions written by people new to problem solving. Solutions for harder problems are mostly written by good coders and reading them itself helps you study as well.
  • It can be seen as an additional reward for passing pretests of a hard problem.

Of course, this is just my opinion and I know it has a lot of disadvantages as well, but I just want to share ideas and imagine how codeforces contests would be with a different hack system. Any other opinions are appreciated.

Read more »

 
 
 
 
  • Vote: I like it
  • +240
  • Vote: I do not like it