Welcome after the long break in Hack me! (Codeforces Round 277.5 (Div. 2)).

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

Really interesting is fact that the second most hacked problem was the last one, what is not so typical.

Hacks and possible hacks description

489A - SwapSort

In some solutions where people are finding minimum every time, they used the wrong limit for the minimum itself.

For example:

min := -100000000
wskmin := -1           <- where is min
for i in 0,1,...,n-1:
  if(min > tab[i])
     min = tab[i];
     wskmin = i;

was killed by the test:

2
200000000 -200000000

How to deal with it? The first possibility is to set min lower than lower bound of numbers on input (for -200000000 we can choose -200007000 or something similar). Or start with the first element as minimum:

min := tab[0]
wskmin := 0          <- where is min

489B - Бал в БерлГУ

Let's take a look at these submissions: 8725982 and 8731808. The first one was hacked and the second accepted, the only difference is sorting vectors. So the following testcase:

2
2 4
2
3 1

was used to hack the first solution. That was not so rare mistake and such tests were used dozen or so times.

489C - Даны длина и сумма цифр...

Interesting bug (and hard to find) was wrong checking of the condition for solution to exist.

The solution exist if the sum is less or equal than 9*m (from obvious reasons). Some people are forgetting about equal part and the proper test like:

2 18

can kill the nearly good submission.

489D - Невыносимая запутанность бытия

The only two hacks for this problem was maximal testcases which resulted in time limit ex.

489E - Поход

No hacks were used for this problem.

489F - Особые матрицы

Nearly all hacks was killing the slow solution with time complexity O(n^3).

Example of such testcase:

500 0 10000007

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Country	#hacks	Hackers
India	26	abhra73 [6], khandeshb1 [6], atulshgl [4], bernett [2], girish347 [2], ramprakash_k [1], StoneCold_ [1], vishwacs111 [1], rtheman [1], gorv [1], sensiblemadman [1]
Japan	25	atetubou [7], ChronoireSchwarzVI [6], anta [4], zerokugi [3], yuusti [2], zeosutt [2], kmjp [1]
Russia	18	knst [4], mmatrosov [4], kharvd [3], lunawyll [2], danildudin [2], w0w [2], NVAL [1]
Kyrgyzstan	16	Erkin97 [9], Azret [5], tokonuuLu [2]
Egypt	12	Guts [5], mohamednabil00000 [3], Mohammad_Yasser [1], khaledA [1], SmartCoder [1], xa.mohsen [1]
Iran	11	mosiomohsen [6], ashkan_d13 [2], Majid [2], Batman [1]
Ukraine	9	kit9ra [3], vlad8 [2], BigBag [2], aangairbender [1], fiter [1]
Colombia	9	pin3da [4], alan_navarro [3], mavd09 [2]
Uzbekistan	8	Eldor_Zoirov [4], Yura_Sultonov [2], Sirojiddin [1], Shavkat_Aminov [1]
Bangladesh	8	the_redback [4], sahedsohel [3], ImagineWarrior [1]