First time being unofficial :)

Now finally my exams are over. I can once again participate in contests.

Very glad to see another Div3 in small interval! good luck everyone!

Why is it showing registrations completed, does it mean I cant register for the contest now?

expert i'm coming

I appreciate that the testers are arranged such that their usernames' colors form a palindrome.

hope there will be strong pretests as last contest was ruined by weak pretests

"I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over."

phew, unlike last contest ;)

see my profile I will never give div 3 I dont know how so many people solve so fast and ACM-ICPC rules sucks too.

Liked the thanking section!! where he used symmetric colour combinations.. :)

I registered for the contest before today's one (Specialist -> Expert) and it still says I'm in competition. Just to confirm this contest won't be rated for me right.

Hope pretest will be strong, not like last contest

Hi everyone,

I would like to know whether I can start 8 hours following the competition starting time since the starting time is past midnight for me. (I am new to competitive programming).

Thanks very much. Cheers

Now, finally before my exams, I am gonna compete.

And can anyone please spare a minute and tell me in which division do I belong, my rating being 814. Thanks.

Is there any chance of arranging these contests so they are in the evening or weekends. Anyone who has a job can't enter as they will be working.

If I know it early, I'll not get to expert:)

So we penalty of 10 min on the wrong submission and not of 50 points. Right?

Good Luck to Everyone

o sweet lords of coding, help me reach 1200.

Last minute tip ! Open this to side : CF Notifications So that you don't need to wait to see AC's

Last minute tip ! Open this to side : CF Notifications So that you don't need to wait to see AC's

After so long time i'm missing a CF rated contest for my Covid. :'( Hope to come back soon.keep me in your prayer. :(

Oof.

A,B1 == div 3 
B2,C.. == div 2 

A perfect div2 round.

A divison 2 contest with Divison 3 participants.

you should have said to check D2 before D1 instead of B2 before B1 I didn't get how dominoes are placed until i checked D2

Thanks for the great contest :)

lovely problems!

When can I check the testcases?

Problem C was incredibly similar to this problem, so much so that I copied over my solution almost verbatim...

Perhaps you should read the problem B2 before you start solving B1.

Was this meant to be a troll?

This round was too hard for Div. 3

Well I found that pretty tough and it wasn't even meant for me

someone please hack my submission.123523305

what is pretest 2 of B2 ? I was not able to figure out till the end

The problems were really interesting. Kudos to the authors involved! Would have been much better if this round was half an hour longer though

How to solve D1? I tried 3 cases. Got WA on Test 3.

Did I miss anything?

I submitted my solution with 22 seconds remaining. I couldnt see the verdict because the page was just loading. Now when i check in my submissions, there is no submission showing. And guess what, when i submitted it in practise it was accepted. Can i be helped??

B2 felt misplaced, for me B and D shoud have been swapped. Or C and B swapped. Or B, C, D reversed... whatever, I worked much to long on B2, and finally was not able to solve it.

How to solve B2?? I am not able to solve it

:(

i got a WA on test 185 can anyone provide me with a counterexample 123529703

You shouldn't make this contest so hard simply because DIV1/2 participants participate as well..

Isn't this output that my code generates for B2's sample input correct? Showing WA on test 1

1 1 2 3 0 1 2 2 3 3 
1 2 3 4 
1 
1 1 1 0 1 1 1 1 0 0 0 1 0 
1 1 1 2 1 1 1 2 2 2 0 2 2 
1 1 1 2 1 2 2 2 3 3 3 3 0 

why is this submission for E giving WA 123523281 on test case 5 I constructed a

whose states describe that we have arrived at i th point in the prefix with j moves done. To do that I first precalculate the

which says the number of elements in the suffix

such that the elements after the ith index (including i) have

, i.e. we have done j moves and after that j moves the number of elements which are now standing at the required index. Now we can iterate over the moves done and check if

and return the minimum j . please help if you can? The transitions are as follows

second transition is as follows you deleted at the ith index. so

calculates the new sum that should be added now that we have made j moves and only the index after i is affected as the left shifts happen from these indices. Final number of elements which are equal given that we have made j moves are in

and now we can simply iterate over j from 1 to n

happy thing: accepted (during contest)

sad thing: accepted (1 minute after the contest)

worse thing: unfortunately, your solution of problem X has been hacked

worst thing: wrong answer/time limit exceeded in test set X (main test)

Did anyone solve D with DP ? I used dp on columns for each two columns c and c + 1 I may put [0, 1, 2, .., min(n, k)]

they will be placed greedily from top to bottom on column c and c + 1 and the remaining cells on c and c + 1 will contain only vertical dominos, if c == m — 1 i can only place vertical dominos on c;

I really don't know why this works, but I have intuition that when placing the horizontal dominos they can form some kind of connected block, and hence I can try different shapes for this CC

Is it only me Or B2 was harder for it's position?

In today's contest , problems were great but time was less and problems were more.

Trollforces

Two contests ago I reached expert so this was unrated for me, yet I was only able to solve A and B1. Clearly I still don't deserve my rating

Help needed! There is something wrong with my lambda expression below, but I have no idea why it turned out this, from my point of view, both a & b is in the range of [0, n), but it can be some invalid value, more exactly in this code, when n >= 17, it would be a mess. I would appreciate it if anyone could help!

#include <bits/stdc++.h>
using namespace std;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int t;
    cin >> t;
    while (t--) {
        int n; cin >> n;
        vector<int> sz(n), r(n);
        for (int i = 0; i < n; i++) {
            r[i] = i;
        }
            sort(r.begin(), r.end(), [&](int a, int b){
//                 cout << "a = " << a << " b = " << b << '\n';
                if (a < 0 || a >= n || b < 0 || b >= n) {
                    cout << "@" << a << ":" << b << ":" << n << '\n';
                    return false;
                 }
                return sz[a] <= sz[b];
            });
    }
    return 0;
}

Problem D2 reminded me of this problem if anyone wants to try.

Problem E was very similar (though not identical) to task from XIV Polish Olympiad in Informatics: statement in Polish

How are the multiple answers tested?, like in today's B2

Hi ! I encountered something weird in my submission for todays 'C'.

Firstly I have made a 'vector of vectors' which store the property of each string i.e. the number of a's,b,c,d,e. Then while checking for character 'a', I am sorting this 'vector of vectors' according to the difference between count of a's and rest of characters.

for(i=0;i<n;i++)
    cin>>s[i];

    vector<vector<ll>> v;
    for(i=0;i<n;i++)
    {
       vector<ll> cnt(5,0);
       for(auto x:s[i])
       {
         cnt[x-'a']++;
       }
       v.pb(cnt);
    }
    ll ans=0;
    sort(v.begin(),v.end(),comp1);

But this is getting RTE in the comparator function:

cout<<v1.sz<<" "<<v2.sz<<" sizes of 2 passed \n";

ll sum1=0,sum2=0;
for(auto x:v1)
sum1+=x;
for(auto x:v2)
sum2+=x;

sum1=sum1-2*v1[0];
sum2=sum2-2*v2[0];

if(sum1<=sum2)
return true;
return false;

While Debugging for Test case 2, 2nd test.. I found that the size of 2nd vector passed in the comparator is coming out of be 0 at one stage (but all the vectors in my 'vector of vectors' are of size 5), and obviously RTE is generated there ..

Can somebody tell more about this ambiguous behaviour ? and how to correct it ( while using the comparator function only )

PS: In Comparator i have passed as vector<ll> &v1 only idk why it's showing vector&v1 here. Also my complete code is very ugly, so that's why am only putting snippets here !!

How are the multiple answers tested?, like in today's B2

How to solve C ?? I am not able to solve it.

Can problem A be solved using binary search?

can someone kindly tell me why am I getting a TLE in this code for problem B2 ? It will be very appreciated..thx 123532079

This is not the div.3 we wanted but this is what we needed.

Is there any way to get all test cases? My program for B2 constantly crashes on test 2 case 3901 and I have really no clue what's going wrong. 123544433

Can anybody helps me with my code in E it gives WA on test 4

code: https://mirror.codeforces.com/contest/1551/submission/123549241

Any ideas for F?

Finger crossed,for not to repeat last round hacking drama & to be specialist for the first time which missed yesterday due to hacking drama

Only 4 different characters are needed in D2: 123522856

editorial?

can anyone give hint for C. thanks in advance :)

Can someone kindly tell me why am I getting TLE in this code for problem B2? 123566277. I really don't know why it get TLE T_T

How long does it take to update the rating?

i must say this wasn't div3 contest , problem C was tough for me.

Thanks for Round!

To not keep you waiting, the ratings are updated preliminarily. In a few hours/days, I will remove cheaters and update the ratings again!

Спасибо за раунд!

Can anybody help in memoizing this recursive code for problem E since I get TLE: Problem E

please share hint for C.

please share hint for C.

Внимание!

Ваше решение 123450555 по задаче 1551A значительным образом совпадает с решениями других участников и находится в группе одинаковых решений rkarroy/123446796, oxxyumoron/123450555. Такое совпадение является явным нарушением правил. Отметим, что непреднамеренное утечка тоже является нарушением. Например, не следует пользоваться ideone.com с настройками по умолчанию (публичным доступом к вашему коду). Если вы имеете неоспоримые доказательства, что совпадение произошло по причине использования общего источника, опубликованного до соревнования, то напишите комментарий к посту о раунде со всеми деталями. Подробнее можно прочитать по ссылке http://mirror.codeforces.com/blog/entry/8790. Такое нарушение правил может являться основанием для блокировки вашего аккаунта или других штрафных санкций. В случае повторения нарушений, ваш аккаунт может быть заблокирован.

Здравствуйте! Я писала свой код на личном компьютере, в среде разработки. Возможно, решение совпало с чьим-то другим из-за своей простоты. Я ни с кем не общалась во время раунда, никому не отправляла код. Можно ли что-то сделать, чтобы такие ситуации больше не повторялись? Спасибо!