Look forward to this round. Thanks for offering div 3 and 4!

the pawns strike back

Finally other author than vovuh for div3 contest

Great!

The time link always shows the Moscow time rather than the local time, please fix it

Div4 was an experiment. Keep maintaining the standard of Codeforces.

thanks for changing from div 4 to div 3 .. :D

[deleted]

Thanks for the div3 instead of div4 :)

This weekend is lit , as CF contest at 7pm IST and at 9.30 Codechef Cookoff . Noice

как очки начисляют? в прошлом див3 решил 1 задачу — ушел в минус. зарегался в див4 чтоб полегче — поменяли на див3. ?? если участие не приму тоже минус будет?

MikeMirzayanov Do you have any plan to run Division 4 regularly?

[Исключен]

Where is vovuh :|

First time there will be 8 problems in Div3!!!

Is it rated since Division was changed from 4 to 3?

Every time contest is organised after so many days, I get excited. It's other thing that I'm not able to solve more than 2 or 3 problems in contest.

I'm starting to miss vovuh already. :(

not div 4 Orz

ШК ФИГНЯ

We missing out on a potential DIO meme here xD.

Can anyone suggest best apps for writing code like codeblocks ( other than codeblock) for a windows user

Isn't it unfair that those who have ratings 1599 can participate in the contest and make their ratings 1800+ but those with rating 1601 can't change their ratings?

You will be offered 8 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600

I'm sorry but I have found candidate masters who find questions from div 3 contests interesting.

_The problems for this round were invented MikeMirzayanov and prepared by me and Stepavly._

Please insert by before Sir MikeMirzayanov

Finally a contest after so many days. It will now be rated for me. Excited!

8 problems!! This will be fun.

And here we go "A non-vovuh Div3 round" after consecutive 23 Div3 rounds. Hats off to vovuh for this 23 round streak. Good luck to new authors.

Maybe you could add one or two easier problems and delete the hardest problem, and then the contest could be div3 and div4, just like div1 and div2 in the past.

Will the problems include sub-tasks?

Can someone elaborate on what this line means:

do not have a point of 1900 or higher in the rating.

Good luck to all! Live solving the problems 15 mins after the contest finishes:

https://youtu.be/gFepyRGn1vs

Only on Algopedia!

Here we go, 6 register buttons.

To be honest,vovuh & MikeMirzayanov always makes nice problemset:)

Eid Mubarak to all the contestants. Hope it will be a great contest for us before EID.

It is div4, lol.

[deleted]

It should not have been a div3.

I didn't receive a reminder email

Video Tutorial for today's G

Quick editorial in Python. For more editorials visit this discord: http://interview.solutions

Question A

def question_A(a, b):
    a, b = sorted([a, b])
    return max(2 * a, b) ** 2

Question B

def question_B(n, s):
    s.sort()
    return min(s[i+1] - s[i] for i in range(n - 1))

Question C

def question_C(n, a):
    odds, evens = [], []
    for x in a:
        if x & 1:
            odds.append(x)
        else:
            evens.append(x)

    if len(odds) & 1 == 0:
        return "YES"

    if any(abs(o - e) <= 1 for o in odds for e in evens):
        return "YES"

    return "NO"

Question D

def question_D(n, k):
    factors = []
    for d in range(1, int(n ** 0.5) + 1):
        if n % d == 0:
            factors.append(d)
            factors.append(n // d)
    factors.sort(reverse = True)
    for d in factors:
        if d <= k:
            return n // d

Question E

01234
11234
22234
33334
44444

def question_E(n, matrix):
    for r, row in enumerate(matrix):
        for c, val in enumerate(row):
            if (
                val and
                r+1 < n and not matrix[r+1][c] and
                c+1 < n and not matrix[r][c+1]
            ):
                return "NO"
    return "YES"

Question F

def question_F(n, m, words):
    def neighbors(word):
        ans = {word}
        for i in range(m):
            for c in ALPHABET:
                ans.add(word[:i] + c + word[i+1:])
        return ans

    intersection = neighbors(words[0])
    for i in range(1, n):
        intersection &= neighbors(words[i])

    if not intersection:
        return "-1"
    return intersection.pop()

Question G

def question_G(R, C, horiz_ones, vert_ones):
    if R * horiz_ones != C * vert_ones:
        return False

    ans = [[0] * C for _ in range(R)]
    for r in range(R):
        for c in range(horiz_ones * r, horiz_ones * (r + 1)):
            ans[r][c % C] = 1
    return ans

Question H

def question_H(n, m, a: List[int]):
    k = 2 ** m - n
    median_index = k - 1 >> 1
    a.sort()

    lo, hi = 0, 2 ** m - 1
    while lo < hi:
        mi = lo + hi >> 1
        i = bisect(a, mi)
        if x - i < median_index:
            lo = mi + 1
        else:
            hi = mi

    return bin(lo)[2:].zfill(m)

The input of problem H is too shit.

Problem G better version: https://vjudge.net/problem/LightOJ-1330

Solution available on net.

1st time I solved 6 questions in a contest. Yipee!!

Can anyone help me with what peculiar case can be in Case#2 of problem F ?
I kept getting WA on Case#2.

G is same as lightOj 1330.

Why greedy isnt working for G?

Can someone tell me why this got TLEd - https://codeforces.com/contest/1360/submission/81243429 and this got accepted - https://codeforces.com/contest/1360/submission/81245539

Both are exactly the same code.

Seriously it's div3. Nope. I think it's the actual div4. Where you would have trivial A, B, C, D, E and not so trivial F, G and really hard H. G was super cool though. Felt like a fool after solving this.

The input data of Problem H is 6MB at worst. Using cin will get TLE, using scanf will not get data because of strange '\n', using some other library also fail. A problem's difficulty should be how to solve it, not how to input it!!

MikeMirzayanov Does increasing the number of questions of DIV4 makes the round DIV3? I hope thats not true for DIV2 round.

I actually spent more time debugging than reading and thinking combined..

Can anybody kindly show me a test case where this bruteforce(!) solution fails?

I hope this is the first and last div3 that you organised.

Can I see due to which test case my solution was hacked>?

What is the best time complexity one can achieve for problem F ?

For the first time in my life solved 5 problem. Thanks to the authors.

In F , I used the brute force concept and my run time complexity was O(n^3*m^2). How to solve it with larger constraints ?

This div3.5 contest was awesome

I think it was better to keep it div4. Div 3 E F problems are generaly much harder than all of these problems.

MikeMirzayanov

This two people are copying codes i guess https://codeforces.com/contest/1360/submission/81303569 and https://codeforces.com/contest/1360/submission/81306780 other solutions of them are also similar. Their previous contest submission are also same. Sorry for bad english. Please look into such acts.

Edit: I just saw that all their submissions are similar. They are taking plagiarism to next level.

Can anyone help me with what peculiar case can be in Case#2 of problem F ? I kept getting WA on Case#2

https://codeforces.com/contest/1360/submission/81313261

Can anyone help me with what peculiar case can be in Case#2 of problem F ? I kept getting WA on Case#2 https://codeforces.com/contest/1360/submission/81313261

I used bitmask dp to solve F in O(t*(1<<n)*m*n^2) and It got accepted in 31ms ... Can anyone provide a testcase which can find the upper bound of runtime .....here is the submission — 81323908

how did you guys approach, your thought process to find out how to arrange all the one's

I used a network flow to solve G lol. Anyone else?

Can some cool guy explain the fact that when anyone ask "Is it rated",he must get many downvotes

Why do ppl still do that? :) Was that supposed to hide from hack?

=> 81289430

Pretests for Problem D were quite weak..... Lot of problem D solutions were hacked.... Felt demotivated after hacked question, as it affects rankings a lot.....

Has the system testing finished? If so when will the ratings change?

Why am i still unrated even after participating in the contest and given solution 3 problems?

If you had felt that the problems are bit difficult for DIV4 you should have put some easy problems in place of those hard problems and make the contest as DIV4. I think the problems are easy for DIV3.

Will i be awarded points for successful hacks in this contest... If Yes then how will it be adjusted to the final rankings

A very fast system test today after quite some time. Even after the number of participants.

My first screencast. Would take suggestions to improve.

I would like to appreciate MikeMirzayanov and his whole team for an amazing round. There was no queue during the contest and it ran very smoothly. So it was great work by codeforces team. I hope future rounds are going to be the same one as this.

Dang its been almost 3 hours since the system testing finished, how come no rating update yet?

why is my rating not changing even after the final standings of the contest are out

for F question. I haven't copied the code and it is entirely different anyways...please resolve the issue asap. I think this may be caused due to the input reader method. Not the logic of the question. manish_98 solution: https://codeforces.com/contest/1360/submission/81281906 my solution: https://codeforces.com/contest/1360/submission/81299107

update : issue resolved by Mike :)

Funny that my first time I solved 5 problems, I decreased in rate :P

Is there a problem with rating changes because alot of people who had there first contest become master?

Can someone explain how this user went to CM without solving even a single problem?

Wow, is this even real?

What the hell! New Ids becoming Master/International Masters with +800 Rating.

I see many success stories on the way titled "How I became an International master in 2 hours "

I have observed that problems in CF Round #644 (Div 3) were quite easy. Except the last, all problems had 2000+ successful submissions during the contest. Due to this, the rating of participant in 1400-1600 exploded. Adding more to this, new accounts became masters just by solving 2 problems last night. LOLzz.

This might be due to new rating system. However, this completely destroys the motive of the new rating mechanism, that was to reduce creation of new accounts.

I propose two points after seeing what happened:

1. Withdraw the new rating system.

2. Make prev. round unrated for participants who were in 1400-1600 before the contest. As the problems were indeed suitable for Div 4 contests only.

Comment if you agree/disagree with my proposal.