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 |
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] |
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 !!
Exactly the same story here :(. And if it weren't fot that, I will now have ~2335 rating ; d.
Btw, weren't you saying that this contest is not for you :P? http://mirror.codeforces.com/blog/entry/14017#comment-189592
It was just for being last in contribution list and I succeeded.
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.
Great idea, I will try to add it. :)
in the first table, what does Other mean?
does it include verdict like Invalid input and similar?
Yes... one of the: INVALID_INPUT, GENERATOR_INCOMPILABLE, GENERATOR_CRASHED, IGNORED, OTHER...