Invitation to UWCOI 2021 - Rated for All

Hey all!

We would like to invite you all to an online replay contest for UWCOI 2021. UWCOI 2021 is an OI-style contest hosted by the Computing Society of UWCSEA Dover which was used to select members for the UWCSEA Dover team for the Singapore National Olympiad in Informatics for this year. It is also participated-in by several other schools in Singapore. The online replay contest will be held as a round rated for both divisions on CodeChef.

We have also held UWCOI 2020 around a year ago – you can check out the problems here if you wish and get a feel for the contest.

Here are some details:

  • Time: Saturday, 19 December, 2020, 21:00 hrs IST (Indian Standard Time). Please check your local timezone here.
  • Contest Format: 7 OI-style tasks (tasks have subtasks) in 3 hours.
  • There is no time penalty for non-accepted verdicts; however, time will be used as the tiebreak.
  • The contest is rated for both divisions (all ratings).
  • There may or may not be interactive questions.
  • The writers are @smjleo , @astoria and @kimbj0709.
  • The contest is hosted on CodeChef here.

We hope you enjoy the contest!

EDIT: We would like to thank our testers from CodeChef: @akashbhalotia , @aryanag_adm @stevens , @jtnydv25 and @l_returns for helping us out with polishing statements and testdata, as well as giving us valuable feedback. Also, special thanks to @socho for helping us with final contest preparation after participating in the onsite contest.

Thank you for participating! We hope you enjoyed the contest.

A: Hidden Numbers
B: Array Swaps
C: Organisation
D: Efficient Delivery
E: City Mapping 2
F: Binary Puzzle
G: Roman Routing


Hope the questions are interesting for everyone :slight_smile:

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Kindly bother check the time once before you post anything on a public forum.

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Still waiting for last year’s laddus to get credited.
Upd - They got credited.


What takes them so much time for delivering laddus for rated short contests? like for unrated short contests I’ve always received laddus within a week

My bad.

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cool guys

Glad that it was fixed :slight_smile:

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Tomorrows cf round is at 3pm IST

Reminder - Contest starts in 20 minutes!

Thanks for the contest, the problems were really nice! Especially liked the idea behind Efficient Delivery.

Any hints for Binary Puzzle? I feel like it will somehow the use the fact that cnt of numbers in the range [0, 2^n - 1] with odd and even bits are equal, using 0 and 2^n - 1 (only numbers with their bit count) to handle odd length in some manner but can’t get an exact logic.

Knowing that, we should not worried about ratings in contests, just for curiousity, i would like to know, when will be rating of this updated to user profiles, I solved 2 questions but my rating is same as of previous one only…
Thank you in advance.

How to solve D ?

Editorial has already been posted

i am not able to submit my solution as of now, after the contest has ended.

I suggest you to not frame such misleading questions like the “Hidden Numbers” Question because after the contest ended I literally saw some answers being accepted with only 1,number

What’s misleading in it? That’s what you’re supposed to do.

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XD… do even know you know what you are saying :rofl:

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