Aren't you tired after Codeforces Round 282 (Div. 1)?
Did you know...
that when you will be on the list of "best hackers" of the round the row with your handle will be highlighted (if you will be logged in)?
Other posts can be found here, including div2.
Stats
Problem | Successful hacks | Unsuccessful hacks | Other | Sum | Solutions which can be hacked | Accepted solutions | All solutions on final tests |
---|---|---|---|---|---|---|---|
494A - Treasure | 363 (53.23%) | 293 (42.96%) | 26 (3.81%) | 682 | 201 (23.40%) | 658 (76.60%) | 859 |
494B - Obsessive String | 2 (50.00%) | 2 (50.00%) | 0 (0.00%) | 4 | 32 (8.42%) | 348 (91.58%) | 380 |
494C - Helping People | 0 | 0 | 0 | 0 | 6 (17.14%) | 29 (82.86%) | 35 |
494D - Birthday | 0 | 0 | 0 | 0 | 1 (4.76%) | 20 (95.24%) | 21 |
494E - Sharti | 0 | 0 | 0 | 0 | 0 (0.00%) | 2 (100.00%) | 2 |
Hacks and possible hacks description
494A - Treasure
First hack — 10 minutes after start of the contest, 363 hacked solutions and 201 more to hack!
The hacks were simple strings with no solutions like:
(#(
(((#)((
(#(()
It was also test #14 (look below):
((#)(
Pretty and deadly :)
494B - Obsessive String
Here are just congratulations for Alex_2oo8 for making two out of two hacks for this problem. Check them out: 129139 and 129164.
494C - Helping People
494D - Birthday
494E - Sharti
Fastest hackers
Problem | Time | Hacker | Defender | Hack |
---|---|---|---|---|
494A - Treasure | 0:13:12 | MrDindows | I_love_Lindsay | 127888 |
494B - Obsessive String | 1:17:53 | Alex_2oo8 | PAP | 129139 |
Best hackers
Best rooms
Room | #hacks | Hackers |
---|---|---|
11 | 18 | linjek [12], PERNEKHAN [2], Aeon [2], allllekssssa [1], oversolver [1] |
2 | 17 | 9charles [6], nemzs [6], scfkcf [3], HolkinPV [1], Reyiz [1] |
5 | 14 | vitux [12], ImaDra [1], SAKT [1] |
19 | 14 | albertg [9], InheritG [2], xwind [2], pllk [1] |
16 | 13 | TMandzu [8], tomlau [3], Fantasy-zwj [1], agw [1] |
4 | 12 | qwerty787788 [5], sokokaleb [5], bernett [2] |
10 | 12 | Yury_Bandarchuk [5], GlebWin [5], EKGMA [1], kmjp [1] |
32 | 12 | nic11 [8], YakutovDmitriy [2], adiko2008 [2] |
35 | 12 | mbaros [7], alpq654323 [3], bayleef [2] |
21 | 11 | Swistakk [6], Na2a [3], Vladyslav [2] |
Best countries
Yey for Poland for being here for the first time! :)
Country | #hacks | Hackers |
---|---|---|
Russia | 75 | linjek [12], gchebanov [10], Egor [9], nic11 [8], kraskevich [6], qwerty787788 [5], viktorov [5], Milanin [3], lkolt [2], YakutovDmitriy [2], zemen [2], bayleef [2], shilov [2], Lelby [1], HolkinPV [1], SirNickolas [1], oversolver [1], AndreySiunov [1], pitfall [1], VArtem [1] |
Belarus | 46 | vitux [12], vilcheuski [7], nemzs [6], sas4eka [5], Yury_Bandarchuk [5], GlebWin [5], Arthur [3], tourist [3] |
Ukraine | 35 | Dymonchyk [7], RAVEman [6], sdya [5], ballon [4], Maestr0 [4], vanchope [4], MrDindows [3], Vladyslav [2] |
China | 31 | v-guihom [6], Bobgy [6], zscc [4], hiyot [3], InheritG [2], gantians [2], xwind [2], SIO__Five [2], 1A2012 [2], Fantasy-zwj [1], squee_spoon [1] |
Poland | 29 | mnbvmar [8], kostka [7], mateusz [6], Swistakk [6], Keram [1], dj3500 [1] |
Kazakhstan | 19 | Volkswagen [7], Na2a [3], Aeon [2], PERNEKHAN [2], adiko2008 [2], a_kabdygali [1], ImaDra [1], zhabo [1] |
Wow, I am honored. Egor unsuccessfully hacked my solution.
(of course, it proceeded to fail system tests)
Good job. We are waiting for div2 analysis.
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.
Yeah, really nice idea. I will implement it next time. It's partially shown on the second graph (accepted/rejected/hacked), but you are right, it will be better shown with numbers too.
In this round it was: A: 64.36 % (nice!) B: 5.88 % C, D, E with 0%.
Sorry for delay, but it is done already here.
You should probably explain the two hacks on B, as well as that huge wrong answer spike on test 47: many solutions subtract 1 in the end, so they end up printing "-1" instead of "1000000006" for this case.
I'm interested how to come up with testcase that uncovers such bug :P.
Does anyone have an idea for this? I thought about locking this problem, because I thought some people might miss the subtraction with mods, but I couldn't find a good way to exploit it. It turned out no one in my room failed because of it, but still...
Nevermind, I got it. First assume the string is of some convenient form, like bbb...b+acca+bbb...b (acca within a lot of b's), and the string to search for is "a". For this just try things (I tried a single "a" within before, and also "aca" within). Let there be x b's at the beginning and y b's at the end. Then, the answer is the sum of 3(x + 1) + 3(y + 1) for the one element sequences with 1 "a" and no "c"s, (x + 1)(y + 1) for the one element sequences with both "a"s, and 6(x + 1)(y + 1) for the two element sequences, giving 3(x + 1) + 3(y + 1) + 7(x + 1)(y + 1). W|A (why doesn't my link work? see below for link) gives integer solutions, for example x=3366,y=84845.
This works:
Try hacking this solution: 9106264.
Go to wolframalpha.com and search
3*(x+1)+3*(y+1)+7*(x+1)*(y+1)=2000000013, 0<x<100000, 0<y<100000, x+y<100000
.