kostka's blog

By kostka, 10 years ago, In English

Welcome after the long break in Hack me! (Codeforces Round 277.5 (Div. 2)).

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
489A - SwapSort 11 (28.21%) 24 (61.54%) 4 (10.26%) 39 400 (17.22%) 1923 (82.78%) 2323
489B - BerSU Ball 185 (61.26%) 102 (33.77%) 15 (4.97%) 302 427 (18.09%) 1934 (81.91%) 2361
489C - Given Length and Sum of Digits... 8 (11.59%) 59 (85.51%) 2 (2.90%) 69 158 (8.90%) 1618 (91.10%) 1776
489D - Unbearable Controversy of Being 2 (14.29%) 6 (42.86%) 6 (42.86%) 14 38 (4.99%) 724 (95.01%) 762
489E - Hiking 0 0 0 0 23 (41.07%) 33 (58.93%) 56
489F - Special Matrices 21 (55.26%) 13 (34.21%) 4 (10.53%) 38 80 (36.87%) 137 (63.13%) 217

* one of the: INVALID_INPUT, GENERATOR_INCOMPILABLE, GENERATOR_CRASHED, IGNORED, OTHER

Here should be graph.
Here should be graph.

Really interesting is fact that the second most hacked problem was the last one, what is not so typical.

Hacks and possible hacks description

489A - SwapSort

Here should be graph.

In some solutions where people are finding minimum every time, they used the wrong limit for the minimum itself.

For example:

min := -100000000
wskmin := -1           <- where is min
for i in 0,1,...,n-1:
  if(min > tab[i])
     min = tab[i];
     wskmin = i;

was killed by the test:

2
200000000 -200000000

How to deal with it? The first possibility is to set min lower than lower bound of numbers on input (for -200000000 we can choose -200007000 or something similar). Or start with the first element as minimum:

min := tab[0]
wskmin := 0          <- where is min

489B - BerSU Ball

Here should be graph.

Let's take a look at these submissions: 8725982 and 8731808. The first one was hacked and the second accepted, the only difference is sorting vectors. So the following testcase:

2
2 4
2
3 1

was used to hack the first solution. That was not so rare mistake and such tests were used dozen or so times.

489C - Given Length and Sum of Digits...

Here should be graph.

Interesting bug (and hard to find) was wrong checking of the condition for solution to exist.

The solution exist if the sum is less or equal than 9*m (from obvious reasons). Some people are forgetting about equal part and the proper test like:

2 18

can kill the nearly good submission.

489D - Unbearable Controversy of Being

Here should be graph.

The only two hacks for this problem was maximal testcases which resulted in time limit ex.

489E - Hiking

Here should be graph.

No hacks were used for this problem.

489F - Special Matrices

Here should be graph.

Nearly all hacks was killing the slow solution with time complexity O(n^3).

Example of such testcase:

500 0 10000007

Fastest hackers

Problem Time Hacker Defender Hack
489A - SwapSort 01:17:56 taxicoo Amon 124095
489B - BerSU Ball 00:49:53 atom_andythomas Staelth 124072
489C - Given Length and Sum of Digits... 01:11:20 whiteshadow1992 dkat 124084
489D - Unbearable Controversy of Being 01:56:35 NVAL kasitan 124243
489F - Special Matrices 01:38:42 xiaoshua PAP 124139

Best hackers

Hacker Stats Successful hacks Unsuccessful hacks
Erkin97 +9-2 (800) B: 124245 124249 124255 124268 124276 124282 124290 124320 124384
B: 124300 124398
atetubou +7-1 (650) B: 124166
F: 124292 124301 124309 124312 124328 124351

F: 124357
mosiomohsen +6-0 (600) B: 124155 124170 124173 124176 124226 124353

khandeshb1 +6-0 (600) B: 124172 124179 124197 124203 124219 124346

ChronoireSchwarzVI +6-0 (600) B: 124104 124121 124123 124128 124145 124182

abhra73 +6-1 (550) B: 124073 124074 124075 124079 124097 124100


C: 124132

Best rooms

Room #hacks Hackers
69 11 khandeshb1 [6], mmatrosov [4], bktl4ever [1]
92 9 Erkin97 [9]
50 7 SEFI2 [5], prana [2]
82 7 Azret [5], rtheman [1], _PeTruS_ [1]
84 7 ChronoireSchwarzVI [6], fiter [1]
1010 7 atetubou [7]
35 6 abhra73 [6]
66 6 Guts [5], hatsuyuki15 [1]
70 6 mosiomohsen [6]

Best countries

Country #hacks Hackers
India 26 abhra73 [6], khandeshb1 [6], atulshgl [4], bernett [2], girish347 [2], ramprakash_k [1], StoneCold_ [1], vishwacs111 [1], rtheman [1], gorv [1], sensiblemadman [1]
Japan 25 atetubou [7], ChronoireSchwarzVI [6], anta [4], zerokugi [3], yuusti [2], zeosutt [2], kmjp [1]
Russia 18 knst [4], mmatrosov [4], kharvd [3], lunawyll [2], danildudin [2], w0w [2], NVAL [1]
Kyrgyzstan 16 Erkin97 [9], Azret [5], tokonuuLu [2]
Egypt 12 Guts [5], mohamednabil00000 [3], Mohammad_Yasser [1], khaledA [1], Killever [1], xa.mohsen [1]
Iran 11 mosiomohsen [6], ashkan_d13 [2], Majid [2], Batman [1]
Ukraine 9 kit9ra [3], vlad8 [2], BigBag [2], aangairbender [1], fiter [1]
Colombia 9 pin3da [4], alan_navarro [3], mavd09 [2]
Uzbekistan 8 Eldor_Zoirov [4], Yura_Sultonov [2], Sirojiddin [1], Shavkat_Aminov [1]
Bangladesh 8 the_redback [4], sahedsohel [3], ImagineWarrior [1]
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10 years ago, # |
Rev. 3   Vote: I like it 0 Vote: I do not like it

Thanks for making this analysis!

In graph for problem B I can't see colors, black border is too big.

UPD. Also, in problem B links to submissions are not relative

Thanks

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    10 years ago, # ^ |
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    1. Solved.

    2. Now they should be, I didn't know that it can be a problem — sorry.