Блог пользователя kostka

Автор kostka, 10 лет назад, По-английски

Welcome after the long break in hacks' describtion in Codeforces Round 270.

This round had really good pretests, so we didn't have many hacks (81 successful ones), but let's have a look at them.

Stats

Problem Successful hacks Unsuccessful hacks Other Sum
472A - Уроки дизайна задач: учимся у математики 41 (23.03%) 105 (58.99%) 32 (17.98%) 178
472B - Уроки дизайна задач: учимся у жизни 3 (4.35%) 52 (75.36%) 14 (20.29%) 69
472C - Уроки дизайна задач: недетеминированность 28 (20.29%) 38 (27.54%) 72 (52.17%) 138
472D - Уроки дизайна задач: обратные задачи 9 (23.68%) 19 (50.00%) 10 (26.32%) 38
472E - Уроки дизайна задач: учимся у игр 0 0 0 0
472F - Уроки дизайна задач: меняем цель задачи 0 0 0 0
472G - Уроки дизайна задач: увеличиваем ограничения 0 0 0 0
Here should be graph.

Description of hacks

472A - Уроки дизайна задач: учимся у математики

There were no particular errors, most of the hacks were just using some easy to check errors: like using 1 as composite number, bad checking if number is composite (forgetting about squares of number, this is not checking last possible divisor ), etc.

Most common testcase was 17. It is 8+9, but many people were checking numbers until floor from (without it).

472B - Уроки дизайна задач: учимся у жизни

Again, nothing special in this task. There were only corner cases and bad solutions were caused by some minor mistakes in implementation.

472C - Уроки дизайна задач: недетеминированность

Nearly all of the hacked solutions were simply too slow and maximum test with large words simply gave "time limit ex.". Also there were some corner cases like no checking first or last word correctly.

472D - Уроки дизайна задач: обратные задачи

Hacks in this problem were either really simple (like below)

2
0 1
1 0

or killing slow solutions (many people get tle on this task), common (and sad) mistakes were using set in C++ (which is quite slow) or bad-written dsu.

Fastest hackers

Problem Time Hacker Defender Hack
472A - Уроки дизайна задач: учимся у математики 0:46:55 VArtem pagol_coder 116473
472B - Уроки дизайна задач: учимся у жизни 1:11:44 pkhaustov regina8023 116519
472C - Уроки дизайна задач: недетеминированность 0:45:40 kmjp sreemeghana8 116472
472D - Уроки дизайна задач: обратные задачи 1:43:06 harrypotter192 super_cr7 116638

Best hackers

Hacker Stats Successful hacks Unsuccessful hacks
zetamoo +4-0 (400) A: 116640 116669 116675 116700

xiaohao1238 +4-0 (400) A: 116578
C: 116725 116801 116815


dirbaio +3-0 (300) C: 116645 116674 116870

Lelby +3-0 (300) C: 116475 116546 116789

swap +2-0 (200) A: 116556
C: 116686


sublinekelzrip +2-0 (200) A: 116647 116655

Nikitosh +2-0 (200) A: 116536 116677

espr1t +2-0 (200) A: 116510
C: 116649


VArtem +2-0 (200) A: 116473
D: 116642


ichyo +2-0 (200) C: 116565 116607

Schullz +2-0 (200) A: 116651 116710

Best rooms

Room #hacks Hackers
8 4 xiaohao1238 [4]
118 4 zetamoo [4]
9 3 dirbaio [3]
55 3 VArtem [2], venki421 [1]
72 3 ichyo [2], mexmans [1]
91 3 Lelby [3]
98 3 Schullz [2], CNWSYCF [1]

Best countries

Country #hacks Hackers
Russia 20 Lelby [3], Nikitosh [2], gridnevvvit [2], VArtem [2], Schullz [2], Copymaster [1], Gassa [1], Guliash [1], Petr [1], ItsLastDay [1], dalex [1], shilov [1], el_sanchez [1], pkhaustov [1]
China 10 sublinekelzrip [2], CNWSYCF [1], dovegx [1], 123qws [1], Flandre_Scarlet [1], dwellings [1], OpalDshawn [1], cbx [1], zhu081607 [1]
India 10 Balajiganapathi [2], JuanMata [2], swap [2], harrypotter192 [1], venki421 [1], noah07 [1], dare1_09 [1]
Japan 8 kmjp [2], ichyo [2], sugim48 [1], logicmachine [1], yaoshimax [1], kzyKT [1]
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10 лет назад, # |
  Проголосовать: нравится +2 Проголосовать: не нравится

I solved D in contest but in system tests , it got TLE. Later , I just added only one "if" into the code : if(i<j). then it got accepted . What an unlucky day !!

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10 лет назад, # |
  Проголосовать: нравится +18 Проголосовать: не нравится

I think another interesting statistic on this topic might be something like this:

hacked solutions / (hacked solutions + failed systests)

this will show how good were hackers in looking up all errors in other people's solutions.

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10 лет назад, # |
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in the first table, what does Other mean?
does it include verdict like Invalid input and similar?

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    10 лет назад, # ^ |
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    Yes... one of the: INVALID_INPUT, GENERATOR_INCOMPILABLE, GENERATOR_CRASHED, IGNORED, OTHER...