Good luck on the contest everyone!(if you are participating that is)

Lets hope people(like me) losing rating in Global round can gain positive delta in this round :)

Опечатка:

О стипендии:

➡ Работа в одном из самых интересных технологических городов Европы

➡ Размер стипендии до 31 500 евро.

➡ Компенсация за стажировку в OneRagtime (800 евро в месяц)

➡ Возможность работать в OneRagtime на полную ставку по окончанию ($$$->$$$ окончании) обучения

[DELETED]

My chance to become specialist :-P

Such a long announcement

It would be very cool too see in future video editorial from the authors!

P.S Sorry for bad English.

Hope for green.

Is there any points system associated with educational rounds and how do successful/unsuccessful hacks affect the points system (if there is one), ranking and the rating?

Let's just hope that problem A isn't 2 lines of code while problem B requires 3 dimensional dynamic programming and you need to precalculate all the stock market crashes in the next 5 months.

I hope there are no adhoc/constructive/geometry/very mathy problems.

I wish higher problems had higher points :(

.

I have participated in 50 contests! Will i be CM before my 100th contest?

My Last brain cell during contest :/

Ahh life's too stressed ....wake up 12 in the noon pass the time learning algos till 7...then CP till 11 and then Counter Strike till 3 am ,sleep at 4:30 and repeat. I guess i messed up this lockdown .

I wish I can do well in this round!

Delayed by 10 minutes!

Well, it's delayed. Here we go again)

delayed by 10 minutes..duh

Delayed by 10 minutes :(

.

Delayed by 10 mins.Hope the contest to remain rated

Contest has been delayed so I'm here because I don't know what to do with my life for the next 10 mins.

What ever the reason of delay is, I hope the contest doesn't become unrated again.

.

I just pray it don't go unrated.:(

why they extend time , it affects mindset of some coders ,what do u think guys ?

oh,a delayed contest may lead somthing unlucky and I hope the contest will go well.

10 more minutes of TWICE it is :D

I this 10 min I realize how useless I am ....

I this 10 min I realize how useless I am..

Hope to become cyan.

This type of Div 2 B demotivates me very much

Sadist is what you call the person who authored problem B.

bruteForces

I really hated this B because I tried to solve it the wrong way I guess

Some one please tell me about process of B i was trying since 1.5 h but i can't find a answer. Please help me to find out the answer

Can someone tell how to solve B

Gap between B and C was very huge , fucked up in the contest literally fucked up !!

ImplementationForces

UPD:

#include <iostream>
#include <vector>
#include <algorithm>

int max(std::vector<int>& a, std::vector<int>& b) {
    if(a.empty() || b.empty()) return 0;

    int ans, m = (int) b.size();
    std::vector<int> suff(m + 1);

    suff[m] = 0;
    for(int i = m - 1; i >= 0; i--) {
        auto it = std::lower_bound(a.begin(), a.end(), b[i]);
        if(it != a.end()) suff[i] = suff[i + 1] + (*it == b[i]);
        else suff[i] = suff[i + 1];
    }
    ans = suff[0];

    for(int i = 0; i < m; i++) {
        auto it = std::lower_bound(a.begin(), a.end(), b[i]);
        if(it == a.end() || *it > b[i]) it--;
        it = std::lower_bound(b.begin(), b.end(), b[i] + (int) (a.begin() - it) );
        ans = std::max(ans, suff[i + 1] + (int) (b.begin() + i - it + 1));
    }

    return ans;
}

int main() {
    std::ios_base::sync_with_stdio(0);
    std::cin.tie(0);

    int t, n, m, x;
    std::cin >> t;

    while(t--) {
        std::cin >> n >> m;
        std::vector<int> l, r, bl, br;

        for(int i = 0; i < n; i++) {
            std::cin >> x;
            if(x < 0) l.push_back(-x);
            else r.push_back(x);
        }

        for(int i = 0; i < m; i++) {
            std::cin >> x;
            if(x < 0) bl.push_back(-x);
            else br.push_back(x);
        }

        std::reverse(l.begin(), l.end());
        std::reverse(bl.begin(), bl.end());

        std::cout << max(l, bl) + max(r, br) << '\n';
    }
}

Really bad problems

For question D: https://codeforces.me/contest/1494/submission/108942229

Input

3
2 5 7
5 1 7
7 7 4

Participant's output

5
2 1 4 5 7 
4
1 4
2 4
3 5
4 5

Checker comment

wrong answer LCA of 1 and 3 is 4 and c[4]=5, but a[1][3]=7

I think the graph will be

5

4 3

1 2

So LCA of 1 and 3 is 5 but checker says it is 3. I don't understand why ? is there anything wrong with my output format ?

In problem B, you only need to check 4 corners, which is totally 16 situation, and just brute force all of them, If you use if else... if else..... you will probably get WA till the end.

My impression when i see the accepted on B after 1.44 hour continuous trying xD .. I am getting negative delta but still happy xD

I hope to become a potato now.

basically https://codeforces.me/blog/entry/88284?#comment-767085

Is the solution to C a two pointers?

Hey,is there any reason why we had to use complicated language like supervisor etc for Probelm-D? Stating it simply in graph theoretic terms like "There exists a rooted tree, each node has has a number and a value. The value of each node is strictly greater than the value of each of its children. You are given the number of leaf nodes and the value of the lca node of each pair of leaf nodes. Construct any such possible tree". I was so confused for so long thinking the given values for each pair was the minimum of direct supervisors.

VerboseForces

In D, I did the following: if two vertices' common salary is the maximum overall, it means that the root of their tree must have that salary. Thus, we can start with an initial set of leaf nodes, and split them into two sets according to which ones have the max common salary or not. Then create a new root node and recursively process the two sets.

Is that approach incorrect? I can't find a counter example :(

Here's my submission: https://codeforces.me/contest/1494/submission/108943905

Thanks.

Screencast with commentary (the quality will get better when YouTube will process it)

Solution: https://codeforces.me/contest/1494/submission/108942229

Input

3
2 5 7
5 1 7
7 7 4

Participant's output

5
2 1 4 5 7 
4
1 4
2 4
3 5
4 5

Checker comment

wrong answer LCA of 1 and 3 is 4 and c[4]=5, but a[1][3]=7

LCA of 1 and 3 should be 5 but checker says that it is 4. Is there anything wrong ? Is my output format is wrong ?

I solved A and B in a similar manner (brute force). For A, I iterated from 000 to 111 (Binary) and checked every possible string b. For B, I iterated from 0000 to 1111 (Binary) and checked all possible black intersections.

it was a bit different. did anyone else get stuck in B?

:'(

i thought i should output number of edges in problem D :(.

Why sometimes "out of bound" gives WA and sometimes RE for the same compiler on codeforeces?

I think the last educational round was very easy than this one.

what's the wrong with my idea of problem A.. My idea was in a greedy fashion. every balanced parenthesis start with ( and ends with ")". so I checked s[0] and converted all of with "(". then I checked s[n-1] and converted all of them with ")". then, there is only one character(A or B or C) in S. at first, I convert that with ")". after that with "(". then, checked the validity for this two options. But wrong answer. my submission may you help me ?

GraphForces

I know it might be out of context but I wanted to say this for a while.

I think the point system in educational round(also div-3) is a bit unfair. All of the problems are assigned 1 point even though they are in increasing difficulty. For instance if somebody has solved problem A and C but not problem B (unlikely but still happen sometimes) then his ranking would be similar to someone who has solved A and B but not C. Even though the first person was able to solve a tougher problem(theoretically and practically) he is still in the same position as the second person which seems unfair to me.

A problem with higher difficulty should have more points, For instance the score distribution in Edu and div-3 contests should be 1,2,3,4,... so on. What's the problem with this score distribution? Maybe I'm missing something.

Open to criticism :)

sent by mistake

For Div 2B,

Can anyone please help me with the testcase where my code fails? 108917717

I am unable to understand the issue with my code.

.

many of the solutions of F can be hacked with the case

6 7
1 2
1 3
1 4
1 5
4 5
4 6
5 6

there seems other hack case for other participants which couldn't hack with this case too. Is the testcases prepared for the system test strong enough??

Seems like todays winner is not alone check his submissions.

standings

One of shorter solutions for B obtained by factoring out symmetries: 108950466 -(Perl). Idea was to squeeze all posible corner cases. I.e. consecutive n 0 is impossible, and it is symmetric to 0 n in reversed direction.

Can someone tell me case number 78 in test case 2 for problem C? Here is the link to my submission that fails at 78th test so can't figure out why. Thanks!