Let's take a look at Christmas Round (Codeforces Round 284 (Div. 1)).
Because of not-so-good scheduling, I didn't take part in it (neither any of my friends did). In Poland, it is a nice time to spend time with family, not like this. If you are interested how Christmas look like in Poland, check out polishchristmasguide.com.
Ok, enough complaining, let's look at the hacks.
Previous posts can be found here, including post for div. 2.
Stats
| Problem | Successful hacks | Unsuccessful hacks | Other* | Sum | Solutions which can be hacked | Accepted solutions | All solutions on final tests | Hackers efficiency** |
|---|---|---|---|---|---|---|---|---|
| 498A - Crazy Town | 14 (42.42%) | 14 (42.42%) | 5 (15.15%) | 33 | 112 (16.79%) | 555 (83.21%) | 667 | 11.11% |
| 498B - Name That Tune | 5 (50.00%) | 4 (40.00%) | 1 (10.00%) | 10 | 85 (52.80%) | 76 (47.20%) | 161 | 5.56% |
| 498C - Array and Operations | 18 (58.06%) | 5 (16.13%) | 8 (25.81%) | 31 | 79 (22.64%) | 270 (77.36%) | 349 | 18.56% |
| 498D - Traffic Jams in the Land | 0 | 0 | 0 | 0 | 2 (2.33%) | 84 (97.67%) | 86 | 0.00% |
| 498E - Stairs and Lines | 0 | 0 | 0 | 0 | 6 (20.00%) | 24 (80.00%) | 30 | 0.00% |
*one of the: INVALID_INPUT, GENERATOR_INCOMPILABLE, GENERATOR_CRASHED, IGNORED, OTHER.
**suggested by marat.snowbear and Yura_Sultonov — hacked solutions / (hacked solutions + solutions which failed on final tests).
Hacks and possible hacks description
498A - Crazy Town
TBD (if someone is willing to share your hacks/mistakes for this problem, I would be really happy :))
498B - Name That Tune
We had many tle for this problem. Of course there were some solutions with complexity 
, but also as said on the post for div. 2, the problem was quite tight time limit, which may come from need to fail all solutions with wrong complexity.
498C - Array and Operations
Test #26 was quite interesting:
100 50
999999937 999999937 999999929 999999893 999999893 999999893 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999883 999999797 999999797 999999797 999999797 ...
It was the first test with "big numbers" and could give wa/tle/mle depending on mistake.
498D - Traffic Jams in the Land
498E - Stairs and Lines
Fastest hackers
| Problem | Time | Hacker | Defender | Hack |
|---|---|---|---|---|
| 498A - Crazy Town | 0:34:10 | v-guihom | hieudz | 130167 |
| 498B - Name That Tune | 1:38:27 | Nerevar | ivanilos | 130299 |
| 498C - Array and Operations | 0:48:20 | sublinekelzrip | sigma425 | 130179 |
Best hackers
| Hacker | Stats | Successful hacks | Unsuccessful hacks |
|---|---|---|---|
| yeputons | +4-0 (400) | A: 130246 130261 130331 130418 | |
| msg555 | +4-2 (300) | A: 130305 130313 130347 130393 | A: 130328 B: 130424 |
| acmer | +3-0 (300) | C: 130277 130286 130312 | |
| zxqfl | +3-0 (300) | C: 130389 130405 130433 | |
| sublinekelzrip | +2-0 (200) | C: 130179 130227 | |
| rng_58 | +2-0 (200) | C: 130276 130340 | |
| davidlee1999WTK | +2-0 (200) | C: 130279 130291 | |
| kmjp | +3-3 (150) | B: 130344 C: 130249 130294 | A: 130320 130379 C: 130229 |
| maximumSHOT | +1-0 (100) | A: 130275 | |
| KADR | +1-0 (100) | B: 130426 | |
| josdas | +1-0 (100) | C: 130408 | |
| triveni | +1-0 (100) | C: 130343 | |
| subscriber | +1-0 (100) | A: 130368 | |
| HYPERHYPERHYPERCUBELOVER | +1-0 (100) | C: 130310 | |
| yoones.rezaei | +1-0 (100) | B: 130378 | |
| Nerevar | +1-0 (100) | B: 130299 | |
| ACRush | +1-0 (100) | C: 130289 | |
| AGrigorii | +1-1 (50) | A: 130260 | A: 130292 |
| SlavaSSU | +1-1 (50) | A: 130217 | A: 130201 |
| v-guihom | +1-1 (50) | A: 130167 | A: 130166 |
| myown1209 | +1-1 (50) | A: 130192 | A: 130218 |
| TeaPot | +1-2 (0) | B: 130316 | B: 130319 130327 |
Best rooms
| Room | #hacks | Hackers |
|---|---|---|
| 32 | 6 | acmer [3], kmjp [3] |
| 21 | 6 | yeputons [4], ACRush [1], myown1209 [1] |
| 29 | 5 | rng_58 [2], subscriber [1], yoones.rezaei [1], KADR [1] |
| 17 | 4 | zxqfl [3], v-guihom [1] |
| 22 | 4 | msg555 [4] |
| 20 | 3 | TeaPot [1], AGrigorii [1], Nerevar [1] |
| 6 | 2 | davidlee1999WTK [2] |
| 8 | 2 | sublinekelzrip [2] |
| 5 | 1 | maximumSHOT [1] |
| 9 | 1 | josdas [1] |
| 10 | 1 | triveni [1] |
| 16 | 1 | SlavaSSU [1] |
| 30 | 1 | HYPERHYPERHYPERCUBELOVER [1] |
Best countries
| Country | #hacks | Hackers |
|---|---|---|
 Russia | 9 | yeputons [4], TeaPot [1], josdas [1], AGrigorii [1], Nerevar [1], SlavaSSU [1] |
 China | 5 | davidlee1999WTK [2], sublinekelzrip [2], v-guihom [1] |
 United States (USA) | 5 | msg555 [4], ACRush [1] |
 Japan | 5 | kmjp [3], rng_58 [2] |
 Iran | 4 | acmer [3], yoones.rezaei [1] |
 Canada | 3 | zxqfl [3] |
 Korea, Republic of | 2 | myown1209 [1], HYPERHYPERHYPERCUBELOVER [1] |
 Ukraine | 1 | KADR [1] |
 India | 1 | triveni [1] |
 Belarus | 1 | subscriber [1] |
Мне не нравился этот контест, так как взломать было практически ничего, а задачи B и C в div.1 были намного сложнее чем задача А (разница в сложности было намного больше чем это бывает в среднем).
P. S. Это мое субъективное мнение, все равно большое спасибо организаторам раунда.