As most of you have probably seen is that no one has been able to get an accepted solution to the challenge problem. This might be because of “Sat Oct 06 , 19:49 The checker for CHEFTAK is incorrect. It will be repaired soon and all submissions will be rejudged, sorry for the inconvenience.”. Maybe it still hasn’t been fixed, but I think that the challenge itself also have some big issues.
Issue 1. Constraints
The problem states 0 \le Z \le 20, but the test generator will with probability roughly 1/5 violate these constraints.
Issue 2. Floating point numbers and rounding
The problem states that “We are rounding all the resulting numbers to 8 significant digits”, but I question what this means. For example what is the smallest amount of coins I can buy? I need much more details about the rounding than just “rounding all the resulting numbers to 8 significant digits”.
Issue 3. Scoring
The problem description isn’t entirely clear about what the total score is. It says that the score for each test case is c-10. It also says that non-positive score will result in WA, whether this refers to the total score or separately for individual test case isn’t clear.
Issue 4. Rand
In the test generation is says “Assume that the function rand(l, r) generates a uniformly random number between l and r (both inclusive).” My guess is that this is discrete uniform (integers), but that isn’t clear.
I think that all of these issues need to be addressed, and I suggest the following fixes:
Fix for issue 1
If during the test generation Z ever becomes <0 or >20, then restart the whole test generator. This allows for roughly the same distribution while keeping 0 \le Z \le 20.
Fix for issue 2
Truncate user input to 8 digits of precision. So if the user tries to buy 9.123456789, it will be interpreted as 9.12345678. Other than this do every calculation exact without ever using floating point numbers. With this there will never be any problems concerning rounding, while still behaving essentially the same as before.
Fix for issue 3
Let the total score be the sum of scores over all the test cases and define AC as having a non-negative score on all test cases.
Fix for issue 4
Just be clear about rand being discrete.
With these issues fixed I think this would be a really interesting challenge problem, but as it stands it is unusable.
The contest has now been extended twice. There was an update on the 16/10/2018 making some fixes for the problem statement (Still missing fixes for issue 2 and some minor errors in the description). The update also stated that “CHEFTAK has been fixed now.” This is in no way true. This time around you can submit solutions and get an “accepted answer” but nothing really works at all. From looking at the scoreboard and reading the forum I understand the following:
Input format is wrong
There are many many solutions with NZEC. From https://discuss.codechef.com/questions/137534/more-issues-with-oct18-challenge-problem-cheftak I understand that this is probably because of the input given not being the same as the one described in the problem description.
Accepted answers aren’t really accepted
Looking at the highscore shows that everyone that got “accepted” only got 0 points. From https://discuss.codechef.com/questions/137534/more-issues-with-oct18-challenge-problem-cheftak, it seems like even printing invalid output like -1 will give accepted answer.
The internal errors
It is possible to get “internal error”. I’m not entirely sure whats causing this. Maybe a bad output can create an internal error or maybe everything is just buggy.
So nothing is working at the moment! I do not understand how the update states “CHEFTAK has been fixed now.”. I understand that there are other competitions around the corner, but this still isn’t acceptable. This is all just a big big mess!
User algmyr https://discuss.codechef.com/questions/137657/oct18-challenge-cheftaks-testcases-confirmed-to-be-completely-broken found out the problem with the input. For some reason Y and Z are both identically equal to “0.000000”, this might be because of an undefined behavior in C++ when using printf("%f",x) with x being an int. With gcc it simply prints “0.000000”.