While waiting for API to update, (it has been updated already) let's look at hacks in Codeforces Round 281 (Div. 2). That was really good round (even I had some hacks :)).
Previous posts can be found here.
Stats
Problem | Successful hacks | Unsuccessful hacks | Other | Sum | Solutions which can be hacked | Accepted solutions | All solutions on final tests |
---|---|---|---|---|---|---|---|
493A - Вася и футбол | 18 (22.50%) | 20 (25.00%) | 42 (52.50%) | 80 | 249 (13.16%) | 1643 (86.84%) | 1892 |
493B - Вася и борьба | 456 (62.81%) | 178 (24.52%) | 92 (12.67%) | 726 | 509 (29.84%) | 1197 (70.16%) | 1706 |
493C - Вася и баскетбол | 161 (47.35%) | 100 (29.41%) | 79 (23.24%) | 340 | 715 (58.56%) | 506 (41.44%) | 1221 |
493D - Вася и шахматы | 22 (59.46%) | 13 (35.14%) | 2 (5.41%) | 37 | 10 (1.18%) | 837 (98.82%) | 847 |
493E - Вася и многочлен | 0 (0.00%) | 1 (100.00%) | 0 (0.00%) | 1 | 16 (76.19%) | 5 (23.81%) | 21 |
![Here should be graph.](/predownloaded/6c/2e/6c2e993a9fdd3d49e1a3a4b8be92658204ca73ca.png)
![Here should be graph.](/predownloaded/93/68/93685230550f213cfc1ff5513db39687b977cc35.png)
Hacks and possible hacks describtion
493A - Вася и футбол
Hacks were pretty simple: you can hack people who forgot that For each player, Vasya wants to know only the first moment of time when he would receive a red card from Vasya.
We can just give two red cards to someone:
FIRSTTEAM
SECONDTEAM
2
42 h 42 r
43 h 42 r
![Here should be graph.](/predownloaded/6d/32/6d3295994f1ae0ed55c9ba6438b509b2bfcd5067.png)
493B - Вася и борьба
Nearly half thousand successful hacks, good job! Where were mistakes?
First thing is just forgetting about some condition (or wrong implementation of them). This thing is quite individual, so we won't say much about it.
Another one is pretty simple: overflow. Test for such hack:
3
1000000000
1000000000
1000000000
Another problem were problems with lexicographically comparation. For example, some people used string (they are sticking the values for each wrestler). So we can hack them with (for example):
4
55
5
-5
-55
Then we have two same strings: "555" and "555', but they should be different ([55,5] and [-5,55]).
![Here should be graph.](/predownloaded/c3/82/c382e978466472602d70b9d81e9eef27ab688a90.png)
493C - Вася и баскетбол
Heh, even I was hacked in this task. The test who destroyed some solutions wasn't really hard:
1
5
2
5 10
While doing binary_search we can forgot that all points can be for two points )or all for three).
For such test the answer should be 2:4
, while many solutions returned 3:6
.
Another thing was using maximal test (with n = 200000, which may result in TLE or RTE.
![Here should be graph.](/predownloaded/72/a6/72a662c7b6a02680eddb5b7074c8f075c46d4434.png)
493D - Вася и шахматы
I wondered why there were so many wrong answers on test #11. It was just the first test with odd number different than 3! :)
![Here should be graph.](/predownloaded/bc/cc/bcccc6f6190f371d7639bc719a0a50ae313a3140.png)
493E - Вася и многочлен
![Here should be graph.](/predownloaded/e9/02/e902d40316f01479a4a56e860ecbd4b9eb20f415.png)
Fastest hackers
Problem | Time | Hacker | Defender | Hack |
---|---|---|---|---|
493A - Вася и футбол | 0:41:45 | Punter | KAMYAR.DARVISHI | 126756 |
493B - Вася и борьба | 0:18:41 | mirceadino | Ferathorn | 126701 |
493C - Вася и баскетбол | 0:40:28 | FatalEagle | KOHCTAHTIH | 126748 |
493D - Вася и шахматы | 1:01:37 | zhuangzhixiaohao1 | dic_phuc | 126900 |
Best hackers
Best rooms
Room | #hacks | Hackers |
---|---|---|
1005 | 22 | SlavaSSU [8], math10 [3], randomstr [3], ctlin04 [3], Carups [2], tanphatls987 [2], HASP [1] |
1000 | 21 | zxc901 [8], Reza_H [6], onetwothree [5], ahm.kam_92 [1], DiegoCR [1] |
1015 | 17 | Jokser [9], azukun [2], ha1vanka [2], pyru [2], pllk [2] |
1017 | 17 | mirceadino [9], ztxz16 [6], Temirulan [2] |
1002 | 15 | BigBag [10], tom [4], Azat_Yusupov [1] |
1003 | 15 | atetubou [5], 123qws [3], kefaa [2], MadNick [2], rlac [2], sugim48 [1] |
1011 | 14 | Ximera [6], zhabo [4], qwerty787788 [2], HidenoriS [2] |
1014 | 14 | kostka [5], Hasan0540 [5], rivudas [3], osamahatem [1] |
12 | 13 | pranet [9], Illidan [4] |
70 | 13 | arturom [6], gstsclq [3], TheDeliriousWave [3], mowicz [1] |
Here is the only place that I can stand in top 10 :D
Now I can call myself one of the best hackers :D
I have 4 people but I'm not in this list!?
4 hacks weren't enough to be in "top hackers" list.
Looking at countries: it looks like it was interesting bug in problem — I assumed (wrongly) that you should have positive result for hacking (you didn't this round, but still get some of them).
I will correct it, sorry.
oh sorry ...
thanks :)