### kostka's blog

By kostka, 5 years ago, ,

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

LeBron 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


1 3 2 4


or test #26:

1


1


### 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 Snusmumriken OwO 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.

Hacker Stats Successful hacks Unsuccessful hacks
LeBron +17-0 (1700) A: 125124 125128 125143 125151 125155 125171 125176 125187 125192 125198 125206 125210 125216 125233 125296 125391
C: 125538

Egor +15-0 (1500) A: 124774 124781 124790 124792 124794 124795 124796 124798 124799 124802 124804 124812 125062 125184
C: 125378

Maestr0 +16-2 (1500) A: 125084 125093 125100 125116 125145 125164 125168 125186 125195 125199 125224 125232 125241 125245 125394 125437
A: 125190 125221
AlexDmitriev +16-4 (1400) A: 124870 124876 124893 124899 124911 124921 124924 124927 124934 124936 124940 124945 124954 124961 124980 125072

A: 124902 125290 125481
C: 125444
alpha_RAU +15-2 (1400) A: 124919 124923 124926 124931 124935 124952 124959 124966 124972 124977 124983 124991 125030 125358 125377
A: 124942 125387
SashaMN +15-3 (1350) A: 124877 124884 124890 124905 124909 124918 124930 124938 125007 125215 125244 125289 125324 125340 125344
A: 124976 124994 125320
TeaPot +13-0 (1300) A: 124805 124813 124815 124818 124820 124821 124823 124829 124831 124834 124836 124840 124908

chaotic_iak +13-1 (1250) A: 125000 125107 125122 125130 125135 125149 125154 125174 125185 125193 125415 125424 125429
A: 125163
kawatea +12-0 (1200) A: 125110 125120 125131 125152 125161 125167 125189 125280 125493
C: 125355 125373 125381

Cromel +12-1 (1150) A: 124953 124957 124962 124964 124968 124971 124979 124982 124984 124985 124986 125472
A: 124996
sas4eka +12-1 (1150) A: 124856 124862 124865 124868 124880 124885 124887 124913 124915 125027 125293 125505
A: 125705
---Grigor--- +12-1 (1150) A: 124859 124866 124871 124875 124889 124897 124907 124910 124916 124963 125092 125209
A: 125004
hos.lyric +12-2 (1100) A: 124874 124879 124888 124895 124901 124912 124914 124917 124920 124946 125329 125412
A: 124950 124955
SlavaSSU +11-1 (1050) A: 125065 125089 125098 125270 125272 125283 125288 125307 125339 125348 125384
A: 125410
albertg +11-1 (1050) A: 125113 125170 125202 125220 125226 125258 125286 125349
C: 124948 125177 125363
A: 125479

Spooky +11-2 (1000) A: 125019 125091 125102 125111 125115 125136 125142 125146 125156 125162 125402
A: 125053 125346
lovelymoon +10-0 (1000) A: 125425 125446 125457 125465 125469 125473 125498 125522
C: 125137 125260

iSlava +10-1 (950) A: 125212 125218 125222 125229 125230 125235 125249 125259 125281 125336
A: 125308
Riatre +9-0 (900) A: 124779 124784 124785 124786 124789 124803 124808 124811 125589

Neroysq +9-0 (900) A: 125314 125333 125354 125372 125386 125395 125401 125409 125418

yarrr +9-0 (900) A: 124995 124999 125002 125003 125008 125563 125719
C: 125423 125427

alpq654323 +9-1 (850) A: 124850 124852 124853 124860 124861 124867 124965
C: 125468 125475
A: 124854

hiukim +9-1 (850) A: 124816 124822 124826 124830 124837 124839 124851 124883 125213
A: 125625
iamnotfake +11-5 (850) A: 125074 125313 125316 125327 125330 125357 125360 125364 125366 125369 125374
A: 125322 125376 125380 125385 125388
shihanyuan +9-2 (800) A: 125207 125227 125236 125247 125254 125277
C: 125593 125594 125598
A: 125690
C: 125605
anudeep2011 +8-1 (750) A: 125169 125178 125183 125191 125196 125203 125217 125408
A: 125223
himank +7-0 (700) A: 124978 124993 124998 125010 125032 125048 125066

gridnevvvit +7-0 (700) A: 124817 124828 124841 124845 124857 124858 125474

alexandre +8-2 (700) A: 125017 125029 125043 125052 125076 125101 125108 125117
A: 125006 125126
Zool +7-1 (650) A: 124981 125009 125038 125047 125058 125079 125095
A: 125018
csehydrogen +6-0 (600) A: 125134 125160 125175 125188 125214 125238

Kostroma +6-0 (600) C: 125318 125325 125580 125583 125586 125592

chiriacandrei25 +8-4 (600) A: 125067 125114 125138 125158 125165 125172 125181 125197
A: 125075 125109 125121 125595
PashaChemerys +6-0 (600) A: 125459 125482 125489 125499 125518 125559

mxh2888 +6-0 (600) A: 125001 125016 125025 125034 125044 125083

Snusmumriken +6-0 (600) A: 125514 125634
C: 124825 125310 125317 125361

eduardische +6-1 (550) A: 125129 125139 125144 125148 125451 125534
A: 125153
LashaBukhnikashvili +6-1 (550) A: 124864 124878 124882 124894 124898 124903
A: 124906
Eugen +6-1 (550) A: 125250 125257 125261 125301 125338 125419
A: 125304
osank +5-0 (500) A: 125012 125015 125042 125070 125726

kmjp +5-0 (500) A: 124872 124881 124891 124904 124922

VArtem +5-0 (500) B: 125476
C: 125323 125328 125331 125660

gskhirtladze +6-2 (500) A: 125352 125371 125597 125600
C: 125697 125710
A: 125398 125403

Misha100896 +5-0 (500) A: 124833 124838 124842 124925 124937

vas.and.tor +5-1 (450) A: 124777 124783 124787 124791 124869
A: 124780
NSV +6-3 (450) A: 125368 125455 125463 125471 125477 125667
A: 125302 125467 125684
zeliboba +5-1 (450) A: 125300
B: 125565
C: 125417 125573 125653

B: 125614

### 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).

Room #hacks Hackers
23 35 Maestr0 [16], Egor [15], rng_58 [4]
20 25 alpha_RAU [15], Snusmumriken [6], y3eadgbe [4]
33 24 lovelymoon [10], Zool [7], PashaChemerys [6], Sisu [1]
31 23 Spooky [11], shihanyuan [9], BigBag [3]
28 21 AlexDmitriev [16], stevenkplus [3], ACRush [2]
2 19 TeaPot [13], gskhirtladze [6]
12 19 iamnotfake [11], osank [5], _meshanya_ [3]
25 19 Riatre [9], LashaBukhnikashvili [6], subscriber [2], ydc [2]
4 18 kawatea [12], maddoctor [5], hirokazu1020 [1]
5 18 Cromel [12], akashdeep [3], Temirulan [3]
8 18 sas4eka [12], VArtem [5], ptnk_1215_panaka_13 [1]
16 18 mxh2888 [6], Kostroma [6], Misha100896 [5], Omelyanenko [1]
27 18 alpq654323 [9], kmjp [5], No0oB [3], Timur_Keks [1]
1 17 chaotic_iak [13], azukun [4]
22 17 SashaMN [15], zxqfl [2]
32 17 LeBron [17]
13 16 albertg [11], Schullz [4], AndreySiunov [1]
29 16 hos.lyric [12], Gassa [3], viktorov [1]
30 16 Denis1995 [4], M0sTik [4], sokian [3], zhanyl [3], Romchela [2]
9 15 chiriacandrei25 [8], vas.and.tor [5], becauseofyou [2]
21 15 SlavaSSU [11], Lelby [3], LiTi [1]
7 14 anudeep2011 [8], eduardische [6]
18 14 alexandre [8], csehydrogen [6]
14 13 himank [7], zeliboba [5], Logic_zys [1]
15 12 ---Grigor--- [12]
17 12 iSlava [10], Slamur [2]
10 11 Neroysq [9], gsaghinadze [1], GlebsHP [1]
11 11 NSV [6], DmitriyH [3], rembocoder [1], Vax [1]

### Best countries

Country #hacks Hackers
Russia 179 AlexDmitriev [16], Egor [15], SashaMN [15], TeaPot [13], SlavaSSU [11], yarrr [9], gridnevvvit [7], Zool [7], Snusmumriken [6], NSV [6], Eugen [6], Kostroma [6], Misha100896 [5], vas.and.tor [5], zeliboba [5], VArtem [5], knst [4], Denis1995 [4], Schullz [4], azukun [4], Gassa [3], _meshanya_ [3], Lelby [3], DmitriyH [3], sokian [3], Romchela [2], Slamur [2], viktorov [1], rembocoder [1], GlebsHP [1], Timur_Keks [1], Aleksander94 [1], AndreySiunov [1], CleRIC [1]
Ukraine 59 LeBron [17], Maestr0 [16], iSlava [10], PashaChemerys [6], M0sTik [4], BigBag [3], Sherbina_Evgeniy [2], Omelyanenko [1]
China 40 Riatre [9], Neroysq [9], shihanyuan [9], maddoctor [5], zhanyl [3], becauseofyou [2], Logic_zys [1], bzoj2424 [1], JayYe [1]
Japan 38 kawatea [12], hos.lyric [12], kmjp [5], y3eadgbe [4], rng_58 [4], hirokazu1020 [1]
Belarus 26 Cromel [12], sas4eka [12], subscriber [2]
Armenia 24 ---Grigor--- [12], albertg [11], mbaros [1]
India 23 anudeep2011 [8], himank [7], osank [5], akashdeep [3]
Iran 15 Spooky [11], No0oB [3], LiTi [1]
Indonesia 13 chaotic_iak [13]
Canada 11 hiukim [9], zxqfl [2]
Romania 8 chiriacandrei25 [8]
Korea, Republic of 6 csehydrogen [6]
Korea,DPR 6 mxh2888 [6]
Latvia 6 eduardische [6]

• +71

 » 5 years ago, # |   0 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.