Waiting for next round, let's take some time and look at hacks in Codeforces Round 278 (Div. 1). That was really good round for hackers :)
Previous posts (including post for Div. 2.) can be found here.
Stats
Yeah, everyone saw that there were plenty of hacks for problem A. How many exactly?
Problem | Successful hacks | Unsuccessful hacks | Other* | Sum | Solutions which can be hacked | Accepted solutions | All solutions on final tests |
---|---|---|---|---|---|---|---|
487A - Fight the Monster | 460 (80.70%) | 96 (16.84%) | 14 (2.46%) | 570 | 58 (11.09%) | 465 (88.91%) | 523 |
487B - Strip | 8 (42.11%) | 8 (42.11%) | 3 (15.79%) | 19 | 99 (27.58%) | 260 (72.42%) | 359 |
487C - Prefix Product Sequence | 67 (90.54%) | 5 (6.76%) | 2 (2.70%) | 74 | 45 (28.66%) | 112 (71.34%) | 157 |
487D - Conveyor Belts | 0 | 0 | 0 | 0 | 8 (30.77%) | 18 (69.23%) | 26 |
487E - Tourists | 0 | 0 | 0 | 0 | 0 (0.00%) | 1 (100.00%) | 1 |
* one of the: INVALID_INPUT, GENERATOR_INCOMPILABLE, GENERATOR_CRASHED, IGNORED, OTHER
Hacks and possible hacks description
Note: this part is simillar to Div. 2. post (because of reasons :)).
487A - Fight the Monster
I_love_Tanya_Romanova had the most hacks for this problem (16!) and with just two problems solved, he managed to be in top 20 — congratulations!
We can take a look at his room (32), or I should say battleground.
Where were the tricky cases?
Let's look at SashaMN's comment (I have to do the screenshot, because it works much better with his avatar).
Interesting fact is that he hacked successfully 15 times, but his solution didn't pass (sidenote: that was chance for sweet revenge, but nobody use it :))! Where does it bring him.
Also congratulations!
Also, you may need more than 1000HP (what was assumed by many people), so we can hack them with test by eduardische:
1 10 1
99 100 1
1 100 100
and when they use greater number, we can hack them again, with test by Ximera:
1 2 1
99 100 1
1 100 100
487B - Strip
There were some solutions which can get tle (with solution or ). It was possible to get acc with such complexity, but the time limit was quite tight (1 second).
Also some people have problems with negative answers. For example, we have tests #31 and #32:
2 1000000000 2
-1000000000 1000000000
10 3 3
1 1 1 1 1 5 6 7 8 9
The answer is simply -1
, but some people did find the answer.
487C - Prefix Product Sequence
There were two most common hacks:
Test #29 (one and only composite number with answer YES
):
4
with answer:
1 3 2 4
or test #26:
1
with answer:
1
487D - Conveyor Belts
487E - Tourists
Fastest hackers
Problem | Time | Hacker | Defender | Hack |
---|---|---|---|---|
487A - Fight the Monster | 0:38:16 | Egor | Ilya_MSU | 124774 |
487B - Strip | 1:56:39 | VArtem | camypaper | 125476 |
487C - Prefix Product Sequence | 0:53:53 | LLI_E_P_JI_O_K | akovski | 124825 |
Best hackers
I wanted to mention all people who made at least 450 points (it is about 5 successful hacks), so the list is quite long.
Best rooms
Yeah... this is also pretty interesting part. The record was 35 hacks in one room (made mostly by Maestr0 and Egor with help of rng_58).
Sounds funny, but without overflow bug in C i would be just 1 hack away from winning a round — while not solving problem D at all.