Invitation to CodeChef January Lunchtime 2020

I invite you to experience 3 hours of uninterrupted coding experience at the January Lunchtime. This 3-hour contest will offer 5 challenging problems to solve. A showdown to reach the top spot. So sharpen your coding skills and get ready to pack your Lunchtime with a box of Code.

The problem statements of the contest will be available in English, Hindi, Bengali, Russian, Mandarin, and Vietnamese. Also, if you have some original and engaging problem ideas, and you’re interested in them being used in the CodeChef’s contests, you can share them here: Problem Idea Submission | CodeChef.

I hope you will join your fellow programmers and enjoy the contest problems. Joining me on the problem setting panel are:

-Setters: infinitepro (Adithya Dsilva), kingofnumbers (Hasan Jaddouh), farhod_farmon (Farkhod), noobie27 (Ashish Lal), kharyusuf (Yusuf Kharodawala)

  • Tester: teja349 (Teja Vardhan Reddy)

  • Editorialist: taran_1407 (Taranpreet Singh)

  • Statement Verifier: xellos0 (Jakub Safin)

  • Mandarin Translator: sam__2 (Qingchuan Zhang)

  • Vietnamese Translator: songuku95 (Team VNOI)

  • Russian Translator: gomelfk (Fedor Korobeinikov)

  • Bengali Translator: solaimanope (Mohammad Solaiman)

  • Hindi Translator: devils_code (Akash Srivastava)

I hope you will enjoy solving them. Please give your feedback on the problem set in the comments below, after the contest.

#Contest Details:

Time: 25th January 2020 (1930 hrs) to 25th January 2020 (2230 hrs). (Indian Standard Time — +5:30 GMT) — Check your timezone.

Contest link:

Registration: You just need to have a CodeChef handle to participate. For all those who are interested and do not have a CodeChef handle, are requested to register in order to participate.


Top 10 Indian and top 10 Global school students from ranklist will receive certificates and CodeChef laddus, with which they can claim cool CodeChef goodies. Know more here.

Good Luck!

Hope to see you participating!!

Happy Programming !!


Hope to be 5 star this lunchtime, idk hopefully :joy:

Excited , wishing everyone high ratings


I’ll probably do another post-contest stream


@infinitepro you are one of the setters? :slight_smile:
I hope the questions are fun to solve this time :smiley:


Yes, I am one of the setters! :smile:
A set of problems were made by me and my friend for an icoprep contest, which unfortunately never took off. Hence, the problems were proposed for a LTIME so that the community would benefit from it.
Watch out for the story line in all my problems to be used in this (and subsequent) LTIME(s)! They are a major give away on the difficulty level of the problems…


Here it is given only top 5 school students will get prizes ??

The link you’ve posted does not mention anything about prizes, so I’ll just assume you’re talking about Div2. Div2 has only 5 prizes, but @kingofnumbers is talking about Div1 where there are 10 prizes.

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Why 7:30 IST? Doesn’t it usually start at 9:30 IST? Plus it being a Saturday, that time would be more suitable to many.

there is a lot of variance between diff submissions in the tunnel question

all my c++ codes are getting wa on second subtaks where my python one passed easily…the logic is exact same.this led to me wasting a lot of time on this and then finally decided to do it again in python and I got ac…can anybody help on why the cpp one is giving wa?


Lol, I tried debugging it myself (yes, I was stalking your submissions), but it’s not clear to me on why your code fails. Let me try it locally and get back to you!


I thought python mein tle karega so did first in c++…the exact opposite what happens in usual scenario

if this has not happened I might have done subtasks of the last 3 questions and maybe the third question completely



I thought lunchtime only measures rank by the score. I wasn’t sure, that it has panelty with wrong submission and re submition, i got Rank somewhat 2300+ very disappointed from my self. I f***ed up!

There is no penalty - but the time taken to reach the score matters.

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Cook-off is at 9:30 on sunday
Lunchtime is at 7:30 on saturday.
I too agree with you that 9 to 12 would have been better. But maybe for school students 7:30 to 10:30 is better. Idk I am just guessing why codechef keeps it at 7:30.

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Oh i didn’t knew lunchtime had a syllabus ! But anyways tough problems are always better if you want to improve

There is no penalty with resubmission afaik.
Read rules below contest page.
They break ties by time taken to get AC.

so ioi problems are easier than standard/trivial matrix expo problems just wow.

do try the real ioi problems once and you will understand the difference.

u should not get disappointed by ur rank…

u should get disappointed by ur performance instead…

the penalty is cos u are late to reach score 200

first 2 were easy…i had very less time today and decided to spend 15 mins for contest

I’m so confused :sweat_smile: i have no idea about ioi, but that meme implied that