kostka's blog

By kostka, 6 years ago, In English

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.
Here should be graph.

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.

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.

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.

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.

493E - Вася и многочлен

Here should be graph.

Fastest hackers

Problem Time Hacker Defender Hack
493A - Вася и футбол 0:41:45 Punter SEVES 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

Hacker Stats Successful hacks Unsuccessful hacks
BigBag +10-0 (1000) B: 126720 126727 126734 126735
C: 127137 127169 127259 127291 127669 127708


pranet +9-0 (900) B: 127045 127136 127150 127170 127187 127214 127222 127659 127715

shardex +10-2 (900) A: 127782
B: 126939 126959 126981 127118 127376 127465 127493 127652 127660
A: 127722
B: 127284
ma5termind +9-1 (850) B: 127407 127451 127489 127506 127551 127589 127613 127643 127679
B: 127306
mirceadino +9-1 (850) B: 126701 126702 126706 126711 126726 126768 126807
C: 127600 127714
B: 126778

Jokser +9-2 (800) B: 126960 126973 126987 126992 127055 127063 127069 127073
C: 126832
B: 126925 127037

anta +8-0 (800) B: 126988 127001 127041 127080 127101 127163 127226
C: 127557


mosiomohsen +8-0 (800) B: 126826 126860 126897 126931 126954 126977 127188 127236

Cherish +9-3 (750) B: 126851 126864 126875 127024 127067 127088 127282 127789
C: 127833
B: 126934 127139 127190

mbaros +8-2 (700) B: 126741 126746 126749 126834
C: 127336 127544 127657 127814

C: 127533 127845
SlavaSSU +8-2 (700) B: 126776 127156
C: 126829 126956 126993 127012 127028 127228
B: 126763 126770

zxc901 +8-2 (700) B: 126825 126839 126898 127133 127313
C: 127283 127481
D: 127826

C: 127216 127412

Xerx +7-0 (700) B: 126998 127013 127026 127149 127182
C: 127658
D: 127537



janbolat +7-0 (700) B: 127627 127704 127742 127769 127805 127822 127859

cfcoolwyj +7-1 (650) B: 127305 127330 127343 127357 127366 127409 127621
B: 127401
pulkit_180894 +7-1 (650) B: 126780 126791 126899 127322
C: 127636 127670 127780

C: 127803
FatalEagle +6-0 (600) B: 127240
C: 126748 126757 126795 126866
D: 127791



ahmedameen +6-0 (600) B: 127364 127596 127785 127808 127824 127848

ShiXingxing15 +6-0 (600) B: 126986 127006 127018 127263 127275
C: 127761


toby007 +6-0 (600) B: 127264 127767
C: 127386 127425 127630 127846


arturom +6-1 (550) B: 127044 127050 127058 127068 127130 127135
B: 127836
CJavaPascal +8-5 (550) B: 126771 126773 126783 126793 127009 127243 127597 127701
B: 126752 126760 127021 127743 127762
Ximera +6-1 (550) B: 126833 126894 126907 127197
C: 127419 127525
B: 126764

Aldiyar +6-1 (550) B: 127022 127031 127060 127077 127831 127855
B: 126996
ztxz16 +6-1 (550) B: 126792 126818 127257 127411
C: 126991 127083
B: 126835

Best rooms

Room #hacks Hackers
1005 22 SlavaSSU [8], math10 [3], ZhazhaLi [3], ctlin04 [3], bnick [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], Vankata [2], tavon [2], pllk [2]
1017 17 mirceadino [9], ztxz16 [6], Temirulan [2]
1002 15 BigBag [10], flashion [4], Azat_Yusupov [1]
1003 15 atetubou [5], 123qws [3], kefaa [2], Nurbakhyt [2], rlac [2], sugim48 [1]
1011 14 Ximera [6], ZhandosBolatbekov [4], qwerty787788 [2], HIdenoriS [2]
1014 14 illi [5], Hasan0540 [5], rivudas [3], osamahatem [1]
12 13 pranet [9], Illidan [4]
70 13 arturom [6], gstsclq [3], ProsecutorWave [3], mowicz [1]

Best countries

Country #hacks Hackers
China 68 cfcoolwyj [7], ztxz16 [6], hulixuan [4], sd0061 [4], scau201330340113 [4], cnjzxy [4], hnust_wuzhanhui [4], v-guihom [4], thanksgiving [3], wanxiaowei [3], hnust_zhouchaoyuan [3], 123qws [3], ZhazhaLi [3], Atlantis67 [3], Nature. [3], F-TopCoder [2], curs0r [2], xietutu [1], SilverBullets [1], acmjohn [1], zentorwie [1], xiaowei [1], gwq5210 [1]
Russia 60 SlavaSSU [8], arturom [6], josdas [6], Izaron [5], AZAZ [5], ZharkovGK [4], Bukreyev [4], Loremon [4], goga24 [4], Koblyk [3], bnick [2], qwerty787788 [2], azukun [2], HASP [1], Grand11122 [1], Roman_Gorb [1], danildudin [1], gars1 [1]
India 47 pranet [9], pulkit_180894 [7], ramprakash_k [5], venomous [4], ddt [3], aarshee [3], rivudas [3], pk. [3], vishwacs111 [2], sanket1729 [2], sara_polyn [1], kuldeepfouzdar [1], satyaki3794 [1], saurabh3240 [1], ameya52 [1], siddhanjay007 [1]
Kazakhstan 45 Jokser [9], janbolat [7], Aldiyar [6], arystan_kalimov [5], ZhandosBolatbekov [4], AmanIT [3], Nurbakhyt [2], huansuz [2], Temirulan [2], AmirzhanOral [2], Birjik [1], Tima [1], daler [1]
Vietnam 36 Incomming [7], ganar27 [4], natsukagami [4], gstsclq [3], moontalk [3], fgnjuf [3], nguyenmanhthien98 [2], Sandzz [2], tanphatls987 [2], pnnb [2], trunghieu11 [1], nc.duy [1], agentp.aka.7214tourist [1], SilverLios [1]
Iran 31 mosiomohsen [8], Reza_H [6], haftobisti [6], shamir14 [5], clashofclans [4], MehrdadAP [1], mhadih [1]
Japan 27 anta [8], atetubou [5], hogeover30 [4], Lepton_s [3], Orisano [2], suigingin [2], sugim48 [1], kmjp [1], lrmystp [1]
Bangladesh 25 Mahir [4], underSpirit [3], math10 [3], aerofoil.kite [2], shantanushanto [2], rifat1234 [2], nfssdq [2], ndatta [2], Emruz_Hossain [1], baridcse [1], shibly [1], FlaminRage [1], Punter [1]
Romania 25 mirceadino [9], toby007 [6], Kira96 [3], PlayLikeNeverB4 [2], tavon [2], alex_bucevschi [1], Mikester [1], Hhsqqq [1]
Ukraine 24 BigBag [10], ballon [3], Sherbina_Evgeniy [3], Cyber.1 [3], antik [1], _XuMuk_ [1], kit9ra [1], pro100leo [1], NegaTeeF [1]
Uzbekistan 20 CJavaPascal [8], Sirojiddin [3], Ben_fika [2], yura_sultonov [2], Isfandiyor [2], Azat_Yusupov [1], Jumaboyev_Davlatmurod [1], Farziddin [1]
 
 
 
 
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»
6 years ago, # |
  Vote: I like it +9 Vote: I do not like it

Here is the only place that I can stand in top 10 :D

»
6 years ago, # |
  Vote: I like it +6 Vote: I do not like it

Now I can call myself one of the best hackers :D

»
6 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I have 4 people but I'm not in this list!?

  • »
    »
    6 years ago, # ^ |
    Rev. 3   Vote: I like it 0 Vote: I do not like it

    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.