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Why does a hacked solution display as Accepted?
By txingml, history, 4 years ago, In English

I want to learn a fast solution for

Bubble Cup 13 - Finals [Online Mirror, unrated, Div. 1] B Valuable Paper

https://codeforces.net/contest/1423

So I click here.

And sort all accepted solutions by Execution Time.

The fastest one is https://codeforces.net/contest/1423/submission/94770930.

I read it carefully and found it is wrong. Then I noticed that it already has been hacked. https://codeforces.net/contest/1423/hacks/669563

Why does a hacked solution display as Accepted? I think it can mislead users.

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4 years ago, # |
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Auto comment: topic has been updated by txingml (previous revision, new revision, compare).

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4 years ago, # |
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There is a phase after the end of the system testing called "uphacking". During this phase, anyone can hack anyone's solution but this doesn't affect the contest results. So your solution is still accepted during the contest but in fact it is wrong.

UPD: Uphacking lasts a week if I remember correctly and this phase was invented just to make the final test set stronger. And this is not the same as hacking phase after the end of Div. 3 or Educational Round which lasts 12 hours.

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4 years ago, # |
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This is known as uphacking: Div 1 participants can hack practically any solutions in the week after the contest ended.

From that announcement:

If a hacked solution is a practice (i.e. upsolving), then its verdict will change to “hacked” otherwise its verdict will remain unchanged

I think the motivation is that re-judging solutions a week after the contest ends would bring a lot of problems (Do you retest all solutions on these hacks? What about the standings? Would you also recalculate the rating changes? What if there was another rated contest since this one?). Since this submission was from an official contest (even if unrated), its status remains "Accepted".

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