Regarding Sum OR problem in ICPC 2019 Online Preliminary Round

The Ranklist of online preliminary round of ICPC conducted by CodeChef was modified by removing a question “SUMOR”. Not only our team but many teams from all over India spent their time solving this question and many of them even got AC. But then suddenly they removed the question making the time we spent on that problem useless. That time would have been spent on some other problem which we could have solved. The removal of that problem clearly affected year long practice and time spent. This matter really needs some concern from CodeChef and higher authorities of ICPC India Regionals.
Do you think Codechef Should be more precise in making Problems of ICPC online Preliminary Round??




“Do you think Codechef will be more precise in future in making Problems of ICPC online Preliminary Round??”


Codechef shouldn’t host these Competitions :expressionless:


Will state 4 things here

  • The problem set was the same for everyone. Everyone has been affected
  • You might have “solved” it, but your answer would still be wrong as your solution would not give the optimal answer in every case.
  • If you realised the actual difficulty of the problem by trying to prove the logic of what you planned on doing, you would instantly realise your answer is wrong.
  • And the last point, I bet you agreed on “decision of organisers is final” before signing up. So no point making claims and discussions about the issue. Face the loss and buckle up for the next icpc round (regionals or online round, whichever is relavent)

But your logic was still incorrect. You wasted your time because you thought the problem is easy. But it wasn’t easy. You should have moved to some other problem instead.
This was best solution to this problem after contest.
Before contest ? Yes it could have been better if they did more stress testing.


How can you quantify “easy”? The only measure I can think is the number of submissions. And that told a different story.

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I meant you were trying that question only because it had more number of submissions right ( thinking that it’s easiest in remaining problems) ? Otherwise why would someone not try next problems and waste time in solving this tough ( probably unsolvable) problem.

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Because we didn’t expect an unsolvable problem. If one can’t solve a problem, should he assume that it is unsolvable?


So you mean just because you tried solving an unsolvable problem and your solution matches with author, you should get some points/advantage over other participants ?

(10 chars)

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That’s why I said this was best solution after contest.
Obviously that doesn’t mean it’s totally fair.


@infinitepro Sir,can you kindly tell me why that SUMOR problem is unsolvable?? I came across a solution that solved it in the reverse way…
1)the last number to be remaining will be the greatest number in the array initially
2)check this last number from the mSB. If we encounter a zero,search for the max number that has the bit for that position set.This max number can be precomputed by maintaining heaps for each bit position.
3)Obtain that number,OR it with the previous one,obtain the result and then again check on the result from the position next to where we stopped earlier.
4)The process continues until we find no more number for a particular unset bit in the result or all the numbers in the array have been exhausted.
5)The numbers from the initial array we took in this process will be stored along the way as the previous algorithm proceeds.
6)Now print the sequence in reverse order with the remaining numbers in the array first followed by those numbers that we had stored.
Why will this approach not give optimal results?If you can kindly explain,it will be a help for a beginner like me.
Thanks in advance