Waiting for next round, let's take some time and look at hacks in Codeforces Round 278 (Div. 1). That was really good round for hackers :)

Previous posts (including post for Div. 2.) can be found here.

Stats

Yeah, everyone saw that there were plenty of hacks for problem A. How many exactly?

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

Hacks and possible hacks description

Note: this part is simillar to Div. 2. post (because of reasons :)).

487A - Бьём чудовище!

I_love_Tanya_Romanova had the most hacks for this problem (16!) and with just two problems solved, he managed to be in top 20 — congratulations!

We can take a look at his room (32), or I should say battleground.

Where were the tricky cases?

Let's look at SashaMN's comment (I have to do the screenshot, because it works much better with his avatar).

Interesting fact is that he hacked successfully 15 times, but his solution didn't pass (sidenote: that was chance for sweet revenge, but nobody use it :))! Where does it bring him.

Also congratulations!

Also, you may need more than 1000HP (what was assumed by many people), so we can hack them with test by eduardische:

1 10 1
99 100 1
1 100 100

and when they use greater number, we can hack them again, with test by Ximera:

1 2 1
99 100 1
1 100 100

487B - Лента

There were some solutions which can get tle (with solution or ). It was possible to get acc with such complexity, but the time limit was quite tight (1 second).

Also some people have problems with negative answers. For example, we have tests #31 and #32:

2 1000000000 2
-1000000000 1000000000

10 3 3
1 1 1 1 1 5 6 7 8 9

The answer is simply -1, but some people did find the answer.

487C - Последовательность частичных произведений

There were two most common hacks:

Test #29 (one and only composite number with answer YES):

4

with answer:

1 3 2 4

or test #26:

1

with answer:

1

487D - Ленты конвейера

487E - Туристы

Fastest hackers

Best hackers

I wanted to mention all people who made at least 450 points (it is about 5 successful hacks), so the list is quite long.

Best rooms

Yeah... this is also pretty interesting part. The record was 35 hacks in one room (made mostly by Maestr0 and Egor with help of rng_58).

Best countries

Country	#hacks	Hackers
Russia	179	riadwaw [16], Egor [15], SashaMN [15], TeaPot [13], SlavaSSU [11], yarrr [9], gridnevvvit [7], Zool [7], LLI_E_P_JI_O_K [6], NSV [6], Eugen [6], Kostroma [6], Misha100896 [5], vas.and.tor [5], zeliboba [5], VArtem [5], knst [4], pitfall [4], Schullz [4], azukun [4], Gassa [3], meshanya [3], Lelby [3], DmitriyH [3], sokian [3], Romchela [2], Slamur [2], viktorov [1], rembocoder [1], GlebsHP [1], Timur_Keks [1], ABalobanov [1], AndreySiunov [1], CleRIC [1]
Ukraine	59	I_love_Tanya_Romanova [17], Maestr0 [16], iSlava [10], PashaChemerys [6], M0sTik [4], BigBag [3], Sherbina_Evgeniy [2], Omelianenko [1]
China	40	Riatre [9], Neroysq [9], littlelittlehorse [9], maddoctor [5], zhanyl [3], problem-solved [2], Logic_zys [1], sublinekelzrip [1], JayYe [1]
Japan	38	kawatea [12], hos.lyric [12], kmjp [5], y3eadgbe [4], rng_58 [4], hirokazu1020 [1]
Belarus	26	Cromel [12], sas4eka [12], subscriber [2]
Armenia	24	---Grigor--- [12], albertg [11], mbaros [1]
India	23	anudeep2011 [8], himank [7], osank [5], akashdeep [3]
Georgia	21	alexandre [8], LashaBukhnikashvili [6], gskhirtladze [6], InDaBag [1]
Iran	15	spOoky [11], No0oB [3], LiTi [1]
Indonesia	13	chaotic_iak [13]
Canada	11	hiukim [9], zxqfl [2]
Romania	8	RomeoFantastik [8]
Korea, Republic of	6	csehydrogen [6]
Korea,DPR	6	mxh2888 [6]
Latvia	6	eduardische [6]