Welcome in hacks' statistics in Codeforces Round 278 (Div. 2). That was really nice round for hackers! Many possibilities, many hacks, let's have a look!

Post for Div. 1. contest will be added later (there are pretty many hacks to parse :)) is here.

Previous posts can be found here.

Your comments are always welcome.

Stats

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

Hacks and possible hacks description

488A - Giga Tower

The mistake was pretty easy and pretty nice. Many people assumed that we need to step at most 10 steps. The counterexample is simple something near 0: -5, -6, -7 (we need to reach 8, of course). Simple and really effective. It was checked by the test #10.

488B - Candy Boxes

I am not a big fan of such problems: you know how to deal with it, but you have to fight with all corner cases. So what tests we didn't found on the pretests?

First one is simple:

4
1 3 2 2

Some people forgot about sorting numbers before taking range. So if we simple take range as x₃ - x₀, we have incorrect answer.

Second one is for example:

3
4 8 9

Looking at tutorial's first solution is the second testcase in n = 3 (the answer is 3).

Some people also had some bad outputs (additional numbers, missing numbers in some cases, etc.).

488C - Fight the Monster

Compared to 460 hacks in Div. 1. only 21 hacks in this division is nearly nothing.

Let's have a look at posibilities:

At first, 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! Where does it bring him?

Congratulation!

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

Poor people :)

488D - Strip

There were no hacks in this division. What can we hack?

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.

488E - Prefix Product Sequence

There were no hacks in this division. Again, there were trick cases:

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

4

with answer:

1 3 2 4

or test #26:

1

with answer:

1

Fastest hackers

Best hackers

Best rooms

Best countries

Country	#hacks	Hackers
Uzbekistan	17	Shavkat_Aminov [5], Jamol_Mattiev [4], Isfandiyor [3], Jumaboyev_Davlatmurod [2], Yura_Sultonov [1], Sirojiddin [1], Eldor_Zoirov [1]
India	14	shank_punk [5], aksam [3], vishwacs111 [3], theab [1], shreeshaprabhu [1], ABHISHEK004 [1]
United States (USA)	8	dwoolley3 [4], El_Ectric [4]
Kazakhstan	6	AdilbekZh [3], Xephy [3]
Iran	6	Majid [2], mosiomohsen [2], ATofighi [1], ashkan_d13 [1]
Belarus	5	nemzs [3], volverine [2]