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Invitation to ICO practice contest 1

Hello, everyone. I would like to invite you to the first contest of the ICO prep series.

Problem Setters: Udit Sanghi, Shashwat Goel, Istasis Mishra
Problem Tester: Udit Sanghi
Editorialist: Shashwat Goel

It will be held on 13th October from 8:00 pm to 11:00 pm IST. Link - Contest

The contest will be unrated. Hope you like the problems. There would be 4 problems and 3 hours to them. The problems difficulty would be around CF Div2 B-C-C-D.

UPD: The editorials have been posted:
RAJAPR0: here
ISTA2001: here
TIDURAT: Pending

List of students to be reimbursed for their ICO Registration:

Agniva Basak
Mohammad Zaid
Archit Boobna
Druhin Lamba
Shashwat Chandra

Above selected students are requested to fill the following form to provide us your bank account details:

Please ask your doubts below.

This question is marked "community wiki".

asked 12 Oct, 16:52

mathecodician's gravatar image

accept rate: 8%

edited 14 Oct, 12:43

ista2000's gravatar image

5★ista2000 ♦


Contest announcements should be compulsarily wikified. Thanks :)

(12 Oct, 17:07) vijju123 ♦5★

Being the setter of problem 4, I think I should have realized that. However this was a 3 hour contest and mostly OI problems do tend to be on the longer side. Moreover, the statement 'looked' long. I say this because, half of the statement was a storyline, a quarter was the formal problem and the remaining quarter was just random explanations to ensure people understood it. Unfortunately my attempt to make it easier to understand by writing more backfired very badly. Also, I wanted to put the problem as an example of how complex statement problems are often the easiest, but again this did not happen :/ We will be posting a simplified problem statement right now for this problem and encourage everyone to try it as the idea used is very common in ZCO. The solution will be posted after 24 hours to allow everyone to interpret it and try to solve it. Hopefully your views of the problem will change slightly. I apologize never the less.


answered 13 Oct, 23:23

harrycoda's gravatar image

accept rate: 0%


Oh! Please don't apologize. You made a really great contest with awesome problems and great tests (my n^4lgn solution failed but only passed with some optimization). The fourth problem was good too it was just we had three problems that were already so good so much time was invested in those problems and less time was left for your problem so some people maybe got tired and didn't read your problem. If there were only 2 problems your problem could have got many submissions but nevertheless the problem was great so was the contest. Keep up the good work :)

(13 Oct, 23:31) vatsalsharma_34★

Moreover, the statement 'looked' long. I say this because, half of the statement was a storyline, a quarter was the formal problem and the remaining quarter was just random explanations

I agree that problem looked long. But 3rd and fourth para could be reworded for better understanding. Dont worry, it was a great job as vatsal said. In case you feel in doubt, its never bad to contact your fellow colleagues or someone to review. You will ALWAYS feel "The statement has no problems."

But what matters is that the reader found it simple :3

(13 Oct, 23:38) vijju123 ♦5★

Don't deny that. Thank you for the suggestions!

(13 Oct, 23:51) harrycoda3★

Great contest! I loved the problems. The last one was a bit long to read and I had less time otherwise all problems were good and of accurate level.


answered 13 Oct, 23:25

vatsalsharma_3's gravatar image

accept rate: 15%

thank you.

(13 Oct, 23:31) mathecodician5★

Problem 4 was great!


answered 13 Oct, 23:38

amit94's gravatar image

accept rate: 33%

Hello everyone. How was the contest? Please give your feedback.


answered 13 Oct, 23:06

mathecodician's gravatar image

accept rate: 8%

Tidu doesnt sound female. And Atsi, lol. I get the references :p .

On a serious note, the statement for "Tidu and Ratings" was too long. The problem with such long statements, all full of details is, it takes time to digest. I remember casually reading it and by the time I reached the end of it, I forgot what the initial part was all about :/

Conciseness is a virtue :D. So yes, try to keep problem statements shorter. All other 3 were excellent in terms of clarity, conciseness and fun, but this last one was kind of off.

PS: Before this poor mod gets jam-packed with requests, please add problems to practice if you have that access as well. :3


answered 13 Oct, 23:16

vijju123's gravatar image

5★vijju123 ♦
accept rate: 18%

edited 13 Oct, 23:18

Tidu female where is it written?

(13 Oct, 23:18) mathecodician5★

Atsi is supposed to be female

(13 Oct, 23:19) mathecodician5★

And I have already asked codechef to add them to practice.

(13 Oct, 23:21) mathecodician5★

I think I can term it comment bombing XDXD

(13 Oct, 23:26) vijju123 ♦5★


(14 Oct, 10:41) ista2000 ♦5★

Tidu and Ratings: So here’s a basic hint to understand the problem: An obvious observation is we need to sort by time, that is just an implementation detail. Now, the problem is reduced. We can’t do a contest until we have done the contest with rating lower than it, before it and after the last contest we attempted. So the next contest we must do from our current position must be one such that no contest in between has a rating in between our current contest and the next contest.

The 70 pt solution is within the scope of ZCO, and is a very commonly tested concept so we encourage you to try the problem. The 100 pt solution requires an optimization on this which is a little beyond the scope of INOI as well, but is quite a handy technique. Also, it is intuitive so once you have the 70/80(first subtask can be handled exclusively)pt solution, try to work on it yourself even if you have never tried such an optimization before ;)

We give solvers one more day to attempt the problem before the editorial comes out, we hope you are better equipped to solve it now. If you have any queries, feel free to ask them here!


answered 13 Oct, 23:56

harrycoda's gravatar image

accept rate: 0%

edited 13 Oct, 23:58

plzz add editorials


answered 14 Oct, 00:05

doramon's gravatar image

accept rate: 12%

We did add all the editorials, they are just not linked in the problems.

(14 Oct, 08:34) ista2000 ♦5★
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question asked: 12 Oct, 16:52

question was seen: 321 times

last updated: 14 Oct, 12:43