In 2019, with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds will be held. These will be common rounds for both divisions of 7–9 problems each. The duration of the rounds will be 2-3 hours, depending on the number and complexity of the problems. All such rounds will be rated for all participants. At each such round, 50 brand T-shirts will be handed out, and we will be happy to give T-shirts to all authors and problem testers.

The prizes for the 6-round series in 2019:

• In each round top-100 participants get points according to the table.
• The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
• The best 20 participants over all series get sweatshirts and place certificates.

Current standings after two rounds:

During the past few days, we have done some internal optimizations (thanks, kuviman). Before the start of Codeforces Global Round 3, I want to be absolutely sure that everything works correctly. I ask you to help us to test the system. Please, take part in Testing Round #15 (Unrated). It is unrated, contains 1-2 easy well-known problems. The pretests will be extremely weak to increase the number of hacks. Thanks!

UPD: It seems everything works great. Thanks!

Hello, Codeforces!

Today I’ve released an important update of the Polygon — partial support for advanced properties of resources. The main task that is being solved by this update is to support the development of problems with graders.

In most competitions, participants need to submit a complete solution code, including reading an input reading and an output writing. For example, in Codeforces rounds you solve such kind of problems. However, in some competitions another approach is using: a participant needs to implement the required function or interface.

For example, in a problem statement can be written that in a C ++ solution you need to implement a function that has prototype int sum (int a, int b) and submit the implementation. In this case, a participant has to submit a source code that contains the implementation of this function. Then, in the process of judging this solution for such a problem, an online judge should compile and link into a single executable file the file sent by the participant and a special jury-prepared file that contains the rest of the necessary code (in particular, there will be the function main).

In the case of problem ``A + B’’, such file, which is called a grader, might look like (grader.cpp):

#include <iostream>
int sum(int a, int b);
int main() {
	int a, b;
	std::cin >> a >> b;
	std::cout << sum(a, b) << std::endl;
}

A solution might look like:

int sum(int a, int b) {
    return a + b;
}

Therefore, a grader cannot be independently compiled into an executable file: it also needs a solution to the problem.

And now basic support for such problems in Polygon has been implemented (thanks to PavelKunyavskiy and cannor147 for the help!). I've started with C++ support only.

In order to add grader files, you must upload them as resources, specifying additional advanced properties: that resources are applicable to cpp.* language group, that they are compile-time resources and that solutions need to be compiled with them.

After adding such resources, while compiling solutions, they will be in the same folder with the solution, and those resources that are C++ files will be appended to the compiler command line.

Please note that all additional information for resources is available in the problem descriptor file problem.xml. Also, API is updated (see the documentation for the methods problem.files and problem.saveFile).

Later, the support of some other languages will be added. Also, I’ll add a feature to attach resources in a similar way not to solutions only, but also to validators/integrators/checkers. Of course, you can expect support for such kind of problems on Codeforces. I note that such problems can be used not only in olympiads/contests but also in the educational process. For example, I can easily imagine an exercise on Java, where you need to implement a given interface, and all other routines (unit tests and other things) are hidden in resources files.

P.S. The support of graders appeared for a special reason: today in Russia begins the IOI training camp. The best high school students will compete for the right to represent Russia on International Olympiad in Informatics. I hope, this feature will help the scientific committee to write new problems. And I wish participants every success and luck!

Many thanks to problem authors — Tech Scouts instructors. Please, review the author's solutions. They are beautiful and short. Our community has many to learn from mathematicians!

What do you know about real Mathforces? This is a world full of numbers, theorems and formulas. Are you ready for the adventure full of challenges and dangers in a new world?

Our friends from Harbour.Space University, the International Tournament of Young Mathematicians (ITYM) and St. Paul's International School Barcelona for the second time organize Tech Scouts — two week International summer camp for high school students. I really think it is a valuable and useful initiative.

For some participants the organizers cover participation fee, the decision is based on the results in special online math test and phone interview.

I invite you to take part in Mathforces: Tech Scouts Online Test 2018 (just fun and practice, unofficial, unrated). It was offered to candidates a year ago, in 2018. This year participants can use it as a practice. I think for many of you it will be interesting to compare your math skills. It starts on May/05/2019 11:05 (Moscow time).

The duration of the test will be 2 hours. You will be offered about 20 math questions. Each of them are expected to be solved using math skills. Please refrain from writing code and try to solve problems without any programming.

You can skip questions or re-submit answers during the test. All the answers will be judged after the test ends. Each question costs 1-3 points in case of the correct answer. Please, do not share your answers before the end of the test.

For sure, the test will be unrated.

Please refrain from participation if you have already participated in this test last year.

UPD 1: The problems will be in English.

UPD 2: The tutorials are published.

Hello,

Three days ago I was forced to come back to ITMO (at midnight!) to turn on the server. I was just happy that the night security at the university understood everything and I got into the server room without any issues. It seems the server was overheated and and shut down. Today, I and _kun_ are planning to update a thermal grease in it. We have not done this before (but I watched the video on YouTube). Wish us good luck!

Hi!

I didn't find any blog post about the round. So, let's discuss it. I'm a little bit upset, because I didn't solve C. Actually, on last minutes I wrote the solution which should pass if replace linear searches with binary.

Am I right that now Google doesn't publish tests?

P.S. And abacabadabacaba is right. The standings are completely unusable (

ICPC World Finals 2019 will begin on April 4, 2019 at 11:00 (UTC). This event is the main event of the year in the world of sports programming!

In the past 20 years alone, ICPC participation has increased by more than 2000%. The contest evolved into its present form as a multi-tier competition in 1977, with the first finals held in conjunction with the ACM Computer Science Conference. Last year, ICPC Regional participation included 52,709 of the finest students and faculty in computing disciplines from 3,233 universities in 110 countries. We remind you that in the current world champion is the team of Moscow State University.

Codeforces wishes the teams to show a vivid and interesting contest. We wish to find beautiful solutions, write without bugs and enjoy many accepted problems!

Links:

• Current results
• Official website of the championship
• ICPC News (photo, video about the Finals)
• ICPC Live (broadcast and not only)
• List of the Teams (with Codeforces handles)
• Online Mirror Contest

Hi Codeforces!

Here are some recent improvements here and in Polygon.

Weak and Leaked Passwords

We often hear about password leaks from various services. Considering that having common passwords is a common (but insecure) practice, we've improved Codeforces and Polygon to identify weak or leaked passwords. If on the top of the website you see a message that your password is not secure, then just change it immediately.

Type of the round when creating a contest proposal

This item improves our work with the writers. When creating a contest proposal, please indicate the type of a round. Leave the field empty only if you don't know the type of the round (it is strange).

Calendar

We've fixed errors when synchronizing official Codeforces rounds with the calendar. Now everything should be correct.

I trust this user

Currently, Codeforces provides a mature infrastructure for organizing contests, olympiads and trainings. With the help of domain groups and mashups, competitions of various levels were hosted on Codeforces. The organizers are sometimes not regular users of Codeforces rounds and do not have rights to some of the actions. Now, any red user can confirm his trust in another account, and he will get the right to: write comments/posts, create private groups, create mashups. I hope this will save me from a certain routine of processing such requests.

Confirmation via email when entering Polygon

When you sign in Polygon, your IP-address and browser will be verified. If you didn't use them in the recent past, then you may be asked to sign in with a confirmation email. In this case, just follow the secret link that comes to your email.

Thanks for taking part in the round. I hope you enjoyed the round. It happens that the statements were really easy to understand (thanks to testers). We've got only 38 questions during a round!

int n, m;
cin >> n >> m;
int result = -1;
if (m % n == 0) {
    result = 0;
    int d = m / n;
    while (d % 2 == 0)
        d /= 2, result++;
    while (d % 3 == 0)
        d /= 3, result++;
    if (d != 1)
        result = -1;
}
cout << result << endl;

int n;
cin >> n;
vector<int> a(n);
for (int i = 0; i < n; i++)
    cin >> a[i];
int result = 0;
int len = 0;
for (int i = 0; i < 2 * n; i++) {
    if (a[i % n] == 1) {
        len++;
        result = max(result, len);
    } else {
        len = 0;
    }
}
cout << result << endl;

int n;
cin >> n;
vector<int> q(n - 1);
long long sum = 0;
long long min_val = 0;
for (int i = 0; i + 1 < n; i++) {
    cin >> q[i];
    sum += q[i];
    if (sum < min_val)
        min_val = sum;
}
vector<long long> p(n);
p[0] = 1 - min_val;
forn(i, n - 1)
    p[i + 1] = p[i] + q[i];
bool ok = true;
for (int i = 0; i < n; i++)
    if (p[i] < 1 || p[i] > n)
        ok = false;
if (ok)
    ok = set<long long>(p.begin(), p.end()).size() == n;
if (ok) {
    forn(i, n)
        cout << p[i] << " ";
} else
    cout << -1 << endl;

#define forn(i, n) for (int i = 0; i < int(n); i++)
const int A = 26;
...
int n;
cin >> n;
string l;
cin >> l;
vector<vector<int>> left(A);
vector<int> wl;
forn(i, n)
    if (l[i] != '?')
        left[l[i] - 'a'].push_back(i);
    else
        wl.push_back(i);
string r;
cin >> r;
vector<vector<int>> right(A);
vector<int> wr;
forn(i, n)
    if (r[i] != '?')
        right[r[i] - 'a'].push_back(i);
    else
        wr.push_back(i);
vector<pair<int,int>> p;
vector<int> cl(A), cr(A);
forn(i, A) {
    forn(j, min(left[i].size(), right[i].size()))
        p.push_back(make_pair(left[i][j] + 1, right[i][j] + 1));
    cl[i] = cr[i] = min(left[i].size(), right[i].size());
}
forn(i, A)
    while (cl[i] < left[i].size() && !wr.empty()) {
        p.push_back(make_pair(left[i][cl[i]] + 1, wr[wr.size() - 1] + 1));
        cl[i]++;
        wr.pop_back();
    }
forn(i, A)
    while (cr[i] < right[i].size() && !wl.empty()) {
        p.push_back(make_pair(wl[wl.size() - 1] + 1, right[i][cr[i]] + 1));
        wl.pop_back();
        cr[i]++;
    }
forn(j, min(wl.size(), wr.size()))
    p.push_back(make_pair(wl[j] + 1, wr[j] + 1));
cout << p.size() << endl;
for (auto pp: p)
    cout << pp.first << " " << pp.second << endl;

long long H;
int n;
cin >> H >> n;
vector<long long> a(n);
long long sum = 0;
long long gap = 0;
long long h = H;
for (int i = 0; i < n; i++) {
    cin >> a[i];
    sum -= a[i];
    h += a[i];
    if (h <= 0) {
        cout << i + 1 << endl;
        return 0;
    }
    gap = max(gap, sum);
}
if (sum <= 0) {
    cout << -1 << endl;
    return 0;
}

long long whole = (H - gap) / sum;
H -= whole * sum;
long long result = whole * n;

for (int i = 0;; i++) {
    H += a[i % n];
    result++;
    if (H <= 0) {
        cout << result << endl;
        break;
    }
}

int n;
cin >> n;
vector<int> a(n);
for (int i = 0; i < n; i++)
    cin >> a[i];
map<int, vector<pair<int,int>>> segs;
for (int r = 0; r < n; r++) {
    int sum = 0;                              
    for (int l = r; l >= 0; l--) {
        sum += a[l];
        segs[sum].push_back({l, r});
    }
}
int result = 0;
vector<pair<int,int>> best;
for (const auto& p: segs) {
    const vector<pair<int,int>>& pp = p.second;
    int cur = 0;
    int r = -1;
    vector<pair<int,int>> now;
    for (auto seg: pp)
        if (seg.first > r) {
            cur++;
            now.push_back(seg);
            r = seg.second;
        }
    if (cur > result) {
        result = cur;
        best = now;
    }
}
cout << result << endl;
for (auto seg: best)
    cout << seg.first + 1 << " " << seg.second + 1 << endl;

int n, k, r;
vector<vector<pair<int,int>>> g;
int D;
vector<int> col;

void dfs(int u, int p, int f) {
    int color = 0;
    for (auto e: g[u])
        if (p != e.first) {
            if (color == f) {
                color = (color + 1) % D;
                f = -1;
            }
            col[e.second] = color;
            dfs(e.first, u, color);
            color = (color + 1) % D;
        }         
}

int main() {
    cin >> n >> k;
    g.resize(n);
    vector<int> d(n);
    for (int i = 0; i + 1 < n; i++) {
        int x, y;
        cin >> x >> y;
        x--, y--;
        g[x].push_back({y, i});
        g[y].push_back({x, i});
        d[x]++, d[y]++;
    }
    map<int,int> cnt;
    for (int dd: d)
        cnt[dd]++;
    
    int kk = n;
    D = 0;
    for (auto p: cnt)
        if (kk > k)
            D = p.first,
            kk -= p.second;
        else
            break;
    col = vector<int>(n - 1);
    dfs(0, -1, -1);    
    cout << D << endl;
    for (int i = 0; i + 1 < n; i++)
        cout << col[i] + 1 << " ";
}

Hello, Codeforces!

I am pleased to invite you to Codeforces Round #547 (Div. 3), which will start on Mar/19/2019 17:35 (Moscow time). Everyone whose current rating is strictly less than 1600 is invited to participate officially. All others can take part out of the competition.

It so happened that the schedule of this month is not replete with rounds (coordinators, we hope for you!). Therefore I decided to partially correct the situation. All the problems of this round were invented and prepared by me on the last day of Hello Muscat Programming Bootcamp 2019 and on flights from Muscat to St. Petersburg. I even specially noted the time for preparation: for the current moment (the problems are ready for testing) I spent about 6 hours on their preparation, including inventing some of the problems. I really like working on problems, this is something at the intersection of creativity and programming. I really hope you enjoy the result of my work.

I am in Oman while writing the problems for the round.

The round will be hosted by rules of educational rounds (extended ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over. You will be given 6-8 problems for 2 hours to solve them.

Note that the penalty for incorrect submissions in this round is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participants of the third division, you must:

• take part in at least two rated rounds (and solve at least one problem in each of them),
• do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

I hope a little later a list of thanks to testers will appear instead of this paragraph. So far I only plan to give the round to testing. Many thanks to the testers ivan100sic, KrK, Benq, I_love_Tanya_Romanova, nhho! UPD: And extra thanks to more testers Pavs, PikMike, Narts, anon20016, Stresshoover, Ivan19981305.

Good luck on the round
— MikeMirzayanov

Hello!

We supported the rendering of LaTeX-formulas with MathJax in new posts and comments. Now the formulas will be as beautiful as in problem statements. Drawback: they are displayed not immediately, but redrawn after the page is displayed. Old posts and comments are displayed in the old way (already a lot of old content, backward compatibility is very important). Note that if you edit old post, it will still be displayed in the old style.

Here are some example: $$$1 \le n \le 10^{12}$$$,  $$$c = \sqrt{a^2+b^2}$$$,  $$$i\hbar\frac{\partial}{\partial t}\left|\Psi(t)\right>=H\left|\Psi(t)\right>$$$.

Hey.

Last week I started the experiment.

I believe in semi-automated learning of programming through problem solving. There are clear advantages of this approach: independence of practice from the teacher, good testing of solutions, clear milestones for students, ability of the approach to scale.

The fundamentals of programming in this sense are quite good: it is easy to prepare problems, there is a clear learning plan, and student progress is well understood.

Surely some structured courses for learning the language from scratch already exist. But why not do it exactly the way I like it? IMHO, a set of problems is crucial here. The devil in the details: increase in the level of problems complexity, diversity, lack of requirements in mathematical preparation, and so on. I have teaching experience (OMG, almost 20 years!), some teaching materials from my work with students of Saratov University and the desire to try!

So, experiment. Since February 20, a wonderful girl le.mur has been learning the basics of C ++ from scratch under my supervision and guidance. We agreed that she captures her impressions in a special Instagram account (subscribe, it motivates!) Lena did not study mathematics in any special way, no initial skills in programming and informatics. Every day she practices 2-4 hours. I expect, one homework should be done in 1-4 days. My plan is to minimize individual explanations, as long as it turns out.

I brazenly stole a photo from Instagram

A training plan for the near future (that is, the very beginning) looks like this:

• The concept of a variable, the simplest functions (min, max, abs), problems without conditional operators and loops.
• Conditional operator, both forms (if, if-else). Understanding of scopes of variables, nested if-s. Problems on conditional operators.
• Loop statements: while and for. Problems for the use of loops without additional constructions (that is, they are solved in one loop without nested conditionals/loops).
• Problems to use loops and conditional operators together.
• Problems to use nested loops.

Each item corresponds to one homework and it will contain 10-20 problems on this topic. Further according to the plan, arrays and strings are expected, but they have yet to be reached.

One of the first conclusions that I managed to do for myself: at the initial stage, you should not immerse yourself in unnecessary details, a simplified or incomplete understanding helps to understand the basics. For example, while Lena operates only with integer variables (type int), she always puts curly brackets after control operators, uses only logical && and ||, only approximately understands the meaning of the “using namespace std” magical spell. It seems to me that after obtaining the initial skills, it will be easier to expand understanding with types, additional operators and other details.

I hope that Lena will succeed and she will not lose her motivation to study.

And how did you learn the very basics of programming? What worked well for you?

Hello, Codeforces!

Yesterday slappy advised me to stop writing problems. I will not listen to his advice and will not stop coming up with new problems. Moreover, the idea of problem 1118C - Palindromic Matrix is mine, and I do not consider it bad or unsuccessful.

IMHO, this is a good example of a problem, where an sloppy (almost slappy) implementation leads to a casework, duplication of code and a lot of formulas. On the other hand, a well-turned implementation is devoid of all these drawbacks and easy to write. It seems to me that such feedback about the problem is something of a Dunning-Kruger effect.

In general, this is an important skill of the developer to write such code, which solves the problem reliably, concisely and is not dirty. And if your code smells bad, then instead of the shaming the authors, I urge you to think "can I write a solution to this problem better?". Good way is to read solutions of other participants. You can choose short implementations from experienced participants. If you focus on learning, rather than just participating for fun, this should be the rule: read solutions of other participants (better experienced, choosing short codes or extremely efficient) and learn. The fact that you got “Accepted” does not mean that you have nothing to learn with this problem.

Here is the explanation of my solution which was written in ~10 minutes. Please, read the problem 1118C - Palindromic Matrix if you don’t know the statement. This problem is just a generalization of string palindrome constructing problem on 2D.

In general case there are 3 types of elements of a matrix (I didn’t spend to much time on drawing, the image is not perfect):

Each element in the blue area has 4 equal copies (itself and 3 additional symmetric cells). Each element in the yellow area has 2 equal copies (itself and 1 additional symmetric cell). And the single central cell (the green area) has only the single copy (itself). The yellow and green areas are absent in case of even n.

It means that you can fill the matrix with a greedy approach. At first process the blue area: for each cell take any value with number of occurrences at least 4 and fill the cell and its copies. After it process the yellow area (if any): for each cell take any value with number of occurrences at least 2 and fill the cell and its copy. Finally, process the green area (if any): take any value with number of occurrences at least 1 and fill the cell and its copy.

Easy to see that each time you can take a value with the greatest number of occurrences, so I used priority_queue<pair<int,int>> to maintain values ordered by number of occurrences. The first item in a pair is a number of occurrences, the second item in a pair is value itself. To construct such priority_queue q just use simple code like this:

map<int,int> cnts;
forn(i, n * n) {
    int val;
    cin >> val;
    cnts[val]++;
}
for (auto [key, value]: cnts)
    q.push({value, key});

To implement the rest of code, use simple function to reflect a position to the symmetric (in 1D):

int rev(int i) {
    return n - i - 1;
}

Now the main part of the code is: iterate over blue, yellow, green areas and put values in the matrix (consider all symmetric copies in together):

int m = n / 2;
forn(i, m) // blue area
    forn(j, m)
        put({{i, j}, {i, rev(j)}, {rev(i), j}, {rev(i), rev(j)}});
if (n % 2 != 0) {
    forn(i, m) { // yellow area
        put({{i, m}, {rev(i), m}});
        put({{m, i}, {m, rev(i)}});
    }
    put({{m, m}}); // green area
}

The function put takes a sequence of symmetric positions and put same values on them:

void put(vector<pair<int,int>> pos) {
    auto t(q.top());
    q.pop();
    if (t.first < pos.size()) // can’t do it?
        no(); 
    for (auto [i, j]: pos)
        a[i][j] = t.second;
    t.first -= pos.size();
    q.push(t);
}

So the complete code is very simple and contains only two if statements (almost no casework!).

#include <bits/stdc++.h>

using namespace std;

#define forn(i, n) for (int i = 0; i < int(n); i++)

int n;
priority_queue<pair<int,int>> q;
vector<vector<int>> a;

int rev(int i) {
    return n - i - 1;
}

int no() {
    cout << "NO" << endl;
    exit(0);
}

void put(vector<pair<int,int>> pos) {
    auto t(q.top());
    q.pop();
    if (t.first < pos.size())
        no();
    for (auto [i, j]: pos)
        a[i][j] = t.second;
    t.first -= pos.size();
    q.push(t);
}

int main() {
    cin >> n;

    map<int,int> cnts;
    forn(i, n * n) {
        int val;
        cin >> val;
        cnts[val]++;
    }
    
    for (auto [key, value]: cnts)
        q.push({value, key});

    a = vector<vector<int>>(n, vector<int>(n));
    int m = n / 2;

    forn(i, m)
        forn(j, m)
            put({{i, j}, {i, rev(j)}, {rev(i), j}, {rev(i), rev(j)}});
    if (n % 2 != 0) {
        forn(i, m) {
            put({{i, m}, {rev(i), m}});
            put({{m, i}, {m, rev(i)}});
        }
        put({{m, m}});
    }

    cout << "YES" << endl;
    forn(i, n) {
        forn(j, n)
            cout << a[i][j] << " ";
        cout << endl;
    }
}

— MikeMirzayanov

Hi Codeforces!

February 2019 is already on the calendar, which means that I was late with the report for 2018. Better late than never! Let's remember last year.

In 2018, _kun_, 300iq and arsijo joined the team of coordinators. The work of the coordinators is headed (and is the coordinator of the coordinators) KAN. I really hope that a more measured schedule of preparing rounds by a large team of coordinators will give a better insight into the contests. The main innovations in the platform are implemented by me and the developers kuviman, fcspartakm, MaximShipko. Great work on the organization of events and prizes mailing was done by gKseni.

Special thanks to the writers of the problems and testers. It is your content that charges the community with life and unites all of us. Thank you for the problems!

And now let's summarize the 2018th year.

Partner Events

We are pleased to hold programming competitions with companies or for companies. I'm sure this is a great way to support the community of young programmers and hire talented candidates. Here is a list of our main partners this year:

• Telegram and personally Pavel Durov is supporting Codeforces activities for many years, every regular round is held with their help, thank you!
• VK, VK Cup — team competition for young Russian-speaking programmers with a series of elimination rounds and finals in St. Petersburg
• Mail.Ru, Mail.Ru Cup — open individual programming competition, consists of several stages, Technocup — open competition for schoolchildren
• Harbour.Space University — a series of educational rounds, the selection of summer school Tech Scouts
• Lyft — a two-level competition with the Final at Lyft headquarters (California) and the mirror contest for worldwide participants
• Avito, Avito Code Challenge and Avito Cool Challenge — open partnership rounds targeting a wide international audience
• Microsoft, Microsoft Q # Coding Contest — unusual quantum computing competition
• AIM Tech — open partnership round targeting a wide international audience
• Huawei — research competition (marathon) with elements of machine learning
• IQ Option — private round as a corporate training

Hello!

It is always satisfying and important for me when former contest participants offer their help to the community and support the development of programming competitions. And now I am in a hurry to share the news that thanks to the support of XTX Markets and the personal participation of Yuri Bedny and Alexander Gerko, we are launching a new line of Codeforces Global Rounds. Hooray!

Like many of you, I had never heard of XTX Markets before but it is one of the largest quantitative-driven electronic liquidity providers in the world. I understand little about the financial sector, but with their 34,148 cores and 42 petabytes of usable storage in their research cluster, XTX’s rapid growth and strong market share globally speak for themselves.

So, in 2019, with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds will be held. These will be common rounds for both divisions of 7–9 problems each. The duration of the rounds will be 2-3 hours, depending on the number and complexity of the problems. All such rounds will be rated for all participants. At each such round, 50 brand T-shirts will be handed out, and we will be happy to give T-shirts to all authors and problem testers.

I will be very happy for Codeforces to work with the best authors of the problems. I hope that the XTX Markets initiative will allow for interesting and testing rounds that will delight community members! We have the opportunity to pay $800, double fee, for the preparation of a full set of problems (for some rounds we may collect problems from different authors).

The first Global Round will take place very soon — starting Feb/07/2019 16:35 (Moscow time). I hope you will enjoy the round!

— MikeMirzayanov

Привет, Codeforces!

Закончился первый тур олимпиады. Надеюсь, что скоро участники поделятся своими впечатлениями от задач и результами. В этом году впервые Codeforces участвовал в проведении этой олимпиады — 12 регионов принимали участие на нашей платформе. Есть кто из участвующих? Как впечатления? Кажется, всё работало без сбоев. Очередей не было.

Дорешивать задачи можно в Тренировках по ссылке 2018-2019 Всероссийская олимпиада школьников по информатике, региональный этап, 1 тур.

UPD: Закончен второй тур. По ссылке Тренировках можно дорешивать и задачи 2-го тура: 2018-2019 Всероссийская олимпиада школьников по информатике, региональный этап, 2 тур.

Hello!

The shortest news on Codeforces. I added support for Microsoft Visual Studio C ++ 2017. The solutions are compiled with the command line cl /std:c++17 /W4 /F268435456 /EHsc /O2 /DONLINE_JUDGE %1.

Привет!

Совсем скоро состоится региональный этап РОИ. В этом году Codeforces присоединяется к проведению, и некоторые регионы будут писать олимпиаду на базе Codeforces.

Для проведения олимпиады мной были пописаны некоторые элементы функциональности Codeforces и Polygon. Теперь, в Полигоне можно не только устанавливать политики начисления баллов для групп тестов и их зависимости, но и рекомендуемую для тестирующей системы политику отображения информации о тестировании. Как и на Всеросиийских олимпиадах, поддержаны следующие политики:

• NONE — не показывать в отчете информацию о тестировании группы,
• POINTS — показывать только баллы за группу тестов,
• ICPC — показывать вердикт до первого упавшего теста (включительно),
• COMPLETE — показывать все вердикты (в этом случае группа тестируется полностью, даже если оценивается только её полное прохождение).

В тестировании на Codeforces было поддержано прерывание групп тестов и пропуск их тестирования, если это можно сделать в соответствии с политиками групп.

Кроме того, для организаторов регионов был разработан отдельный интерфейс, который сделает проведение олимпиады простым и комфортным.

Приглашаю всех интересующихся присоединиться к открытому пробному туру региональной олимпиады по адресу https://roi19p.contest.codeforces.com. Просто используйте свой аккаунт Codeforces, чтобы зайти на этот подсайт и примите участие в пробном туре. Обратите внимание, что каждое условие содержит описание политик начисления баллов и отображения отчетов. По задачам можно задавать вопросы (тестируем всё!), но я не могу обещать, что смогу ответить на них.

Если что-то работает неправильно, непредсказуемо или неудобно, то пишите комментарий под этот пост.

Спасибо!

Congratulations to all the new 2019 year! At this very moment you can make an important wish. Done? I wish it to be fulfilled!

I wish you to become better in the new year, to think better and to meet less often with bugs and mistakes. Let all your solutions be fast, effective and correct!

Later, I will compile statistics for 2018 and publish in the form of an annual report

Now I'd like to remind you most voted posts of 2018. Here is the list of the top 15:

• Codeforces: Problem Difficulties by me, +3158
• Codeforces: Our Steps After DDOS Attack me, +2995
• Hello 2018 by tourist, +2848
• Codeforces: Updates in rating and rounds by me, +1973
• Blogewoosh #1 by Radewoosh, +1798
• Linear Recurrence and Berlekamp-Massey Algorithm by TLE, +1492
• Hello, ITMO! by me, +1331
• Codeforces: Results of 2017 by me, +1319
• Should I start writing regular blogs? by Radewoosh, +1083
• Blogewoosh #6 by Radewoosh, +1075
• Multiple accounts for one person should be banned by dotorya, +1047
• Retiring from rated contests by bmerry, +1038
• Good Bye 2018 by majk, +985
• Stream by Errichto, +973
• Teams going to ACM ICPC World Finals 2018 by Luqman, +938

Happy New Year!

Do you already have a New Year's mood?

And we have traditional gifts!

Change Handle Feature

Hurry! Only until the 10th of January, you can change your handle (but only once)! Note that it will be possible to roll back the changes or change the handle again only after a year. Be careful what you wish for.

You can change your handle to the new one which wasn't used before by anybody or which was used by you before. The links to a profile page with old handle would automatically redirect to the actual profile.

This year we have an improvement. If you took part in at least 10 rounds you can request handle of an inactive participant. It means that the participant should have a period of activity on Codeforces of at most 90 days, this period should be in 2015 or earlier. The inactive participant can’t have posted comments, messages and so on. It can't take part in more than 2 contests. It will be automatically renamed and informed by email. If you can’t change handle to others, it means that some requirement doesn't meet. Please do not ask me to do something with it. I'm not Santa Claus.

Talking about handles I always reminisce the following story. Once a user wrote me the message: "Please change my handle from I_love_Valya to I_love_Sveta, as I no longer love Valya ..."

New Year's Masquerade of Colors and Ranks

Traditional magical tab has appeared in the profile setting. Happy New Year!

Hello,

We have some technical issues for operating with recent problems. If you created a gym/mashup (today or yesterday), it is possible that its submissions are not visible. I'm working on it. Probably, today night it will be a planned maintenance shutdown to fix it.

I think it will not affect Educational Codeforces Round 55 (Rated for Div. 2).

Mike.

Here are merged results of Mail.Ru Cup 2018 Round 1, Mail.Ru Cup 2018 Round 2 and Mail.Ru Cup 2018 Round 3 according to the GP100 scores (see the announcement for the details https://codeforces.com/blog/entry/62355). Best two contests give the summary score of a participant. This table is unofficial yet. But anyway... congratulations to the winnerzzzz!

Hello.

As I wrote into a comment, last round we are faced a strong DDOS-attack which ruined the competition. I don't know who did it, I also don't know reasons to do it. I'm very upset about the situation and ready to make effort to be prepared for such issues.

I spend a lot of time to be ready for such incidents.

Here are steps you need to do to be ready for unexpected failures:

• Join our telegram channel by the link https://t.me/codeforces_official to read urgent news.
• Be sure that you know the password of your Codeforces account. If you don't remember it, just use the password recovery feature. Please, do it right now.
• I've implemented a minimalistic website for replacing the main site in case of emergencies. Now you can only read problems, view you submissions (without any details), submit codes. Probably, later I'll add some more features, but anyway the minimalistic version will have only vital features to take part in a contest. I've deployed it in several places, you can visit any of them by the links: http://m1.codeforces.com, http://m2.codeforces.com, http://m3.codeforces.com. If any of them is unavailable, just use another. Do not use them if the main website is alive.

Hi, Codeforces!

I am glad to announce and invite you to the second launch of my course on algorithms and data structures.

On 7-25 of January, 2019, I will be giving the course "Advanced Algorithms and Data Structures" at Harbour.Space University (Barcelona, Spain). It will be in English, and is not limited to Harbour.Space students — anyone is welcome! Who wants to join?

This course isn't just for Harbour.Space students, it is also open to Codeforces participants, who will be offered a special price, 1000 EUR. The cost does not include travel or accommodation.

The curriculum will include a breakdown of algorithms and data structures, a lot of practical exercises, and emphasis not only on the correctness, but also the beauty and structure of the code. My goal is to make classes that are useful and interesting for both those who want to understand the fundamental CS, and for those interested in programming competitions. And of course, we will have the opportunity to meet and talk. I look forward to share stories about the history of Codeforces and future development plans.

The course will consist of three weeks of intensive training, 5 days in each week, 3 hours per day. The program includes daily lectures and practical exercises. It will not be boring for sure!

Here is the expected course outline:

Harbor.Space University is located in Barcelona (Spain). For users of Codeforces, Harbour.Space is known for active participation in the life of the community of sports programming (partnership with Codeforces in the framework of Educational Rounds). The main activity of the university is teaching (there are bachelor's and master's programs) in the following areas:

• Maths as a Second Language
• Computer Science
• Data Science
• Cyber Security
• Interaction Design
• Digital Marketing
• High Tech Entrepreneurship
• FinTech
• BioTech
• Aerospace Engineering
• SuperCities UrbanTech

Harbour.Space is also proud to announce the Scholarships to study Msc in Robotics in Barcelona. Follow this link for more information about the opportunity and application process.

Register for my upcoming course via this link.

— MikeMirzayanov