Invitation to CodeChef October Lunchtime 2020

We invite you to participate in the CodeChef October Lunchtime — the 3-hour contest which offers 5 challenging problems to be solved, next Saturday, October 31st, 19:30 to 22:30 IST.

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.

I hope you will join your fellow programmers and enjoy the contest problems. The members of the problem setting panel are:

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


The 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.

Video Editorials

You will now also be able to solve your doubts with the help of our amazing educators and their helpful video editorials. Don’t forget to check out our YouTube Channel soon after the contest ends. Hit the Subscribe button so you don’t miss out on any video editorials in the future.

Good Luck!
Hope to see you participating!!
Happy Programming!!


Incoming Xor missiles?


Expecting some bitwise or Problems!!!


Codechef already has trend of setting good xor problems in lunchtimes and cookoffs, @mohammed200218 will continue the legacy I think :stuck_out_tongue:

Guess what ? Even the whole problemset can involve xor :stuck_out_tongue:


The video editorials to the problems are uploaded on Youtube



Why I am too slow? XD

Will this logic work for EFLIP when M=N-2 (Last question)

I make a undirected graph using the edges given. Since M=N-2 it is gaurenteed to not be connected. Then I take all nodes from 1 component and direct it to another component. Would this work.

You are right.
It almost did!! :stuck_out_tongue_closed_eyes: :stuck_out_tongue_closed_eyes:

Yes, that’s the intended solution for this subtask.

Thats extremely unfortunate, didn’t get time to completely implement it. Will prolly miss 6 star to that.

Anyways, really nice questions. Loved the set

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