On 13th June there was Codeforces round #649. In problem D during the round, there were only 137 test cases as the main test, so lot of people got AC during the round but afterward, the number of test cases was increased to 142 and many passed solutions were failing in those test cases. and this is not the first time this happened, In Codeforces Round #637 (Div. 2), problem D had only 24 test cases initially which allowed even greedy solutions to GET AC, which was failing in afterward added test cases. So is there any reason for this happening and will it be solved?
Solution That got AC during round But Failed when new test Cases were added:-
2.Codeforces Round #637 (Div. 2) D
(P.S.:- These solutions got AC even after the system test as at that time there were fewer test cases but Now if you submit them, they won't pass as test cases got increased)
Auto comment: topic has been updated by humblefoolboi (previous revision, new revision, compare).
It probably happened because of uphacking.
So it's not a bug, it's a feature. If a hacked solution was submitted during the rated contest, its verdict will not change.
But these questions were missing basic test cases. Won't it be better that every round has 12 hour hacking period afterward so test cases get improved?
I don't think that it will be implented. The rules of standard rounds remain (almost) unchanged for years. And your suggestion is quite a big change.
In addition, one of the reasons to introduce hacks during the round was to add test cases. And since there are no hacks done to catch this incorrect solution, maybe it is not critical to catch it at all?
But this is my opinion, I'm not a part of administration.
Yeah bro I get it, That's why I wrote this blog so someone from codeforces team can see it, cause mising such basic test cases is not good for round i guess.