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

Hacks and possible hacks describtion

493A - Vasya and Football

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

493B - Vasya and Wrestling

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]).

493C - Vasya and Basketball

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.

493D - Vasya and Chess

I wondered why there were so many wrong answers on test #11. It was just the first test with odd number different than 3! :)

493E - Vasya and Polynomial

Fastest hackers

Best hackers

Best rooms

Best countries

Country	#hacks	Hackers
China	68	coolwyj [7], ztxz16 [6], hulixuan [4], sd0061 [4], scau201330340113 [4], cnjzxy [4], fswuweis [4], v-guihom [4], thanksgiving [3], wanxiaowei [3], hnust_zhouchaoyuan [3], 123qws [3], randomstr [3], Atlantis67 [3], Lyos [3], I_Love_Balabala [2], curs0r [2], xietutu [1], SilverBullets [1], acmjohn [1], zentorwie [1], xiaowei [1], gwq5210 [1]
Russia	60	SlavaSSU [8], arturom [6], josdas [6], Sehnsucht [5], AZAZ [5], ZharkovGK [4], SirNickolas [4], Loremon [4], goga24 [4], Koblyk [3], Carups [2], qwerty787788 [2], azukun [2], HASP [1], Grand [1], Roman_Gorb [1], danildudin [1], gars [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], Dr.I_m_possible [1], siddhanjay007 [1]
Kazakhstan	45	Jokser [9], ZzZZzzzZZZZZzzzzzzzz [7], Xephy [6], arystan_kalimov [5], zhabo [4], amanchik [3], MadNick [2], huansuz1 [2], Temirulan [2], amiro [2], Birjik [1], Tima [1], ImAlsoJoseph [1]
Vietnam	36	llaugusty [7], ganar27 [4], natsukagami [4], gstsclq [3], NgocHai [3], fgnjuf [3], nguyenmanhthien98 [2], RurouniKenshin [2], tanphatls987 [2], pnnb1997 [2], trunghieu11 [1], nc.duy [1], rm-rfslash [1], 1067607 [1]
Iran	31	mosiomohsen [8], Reza_H [6], Alimol [6], shamir0xe [5], Majid [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	lazyM [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], pyru [2], alex_bucevschi [1], Mikester [1], Horea [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	monkey_king [8], Sirojiddin [3], Agabek [2], Yura_Sultonov [2], Isfandiyor [2], Azat_Yusupov [1], Jumaboyev_Davlatmurod [1], Farziddin [1]