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 cdkrot 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 eatmore 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, awoo, 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, cdkrot, 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

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.

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 with 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 an 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 your 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.

UPD: Now you can enter minimalistic websites without a password. In this case, an email with a secret enter link will be sent to you.

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

Here are merged results of Mail.Ru Cup 2018 Round 1 and Mail.Ru Cup 2018 Round 2 according to the GP100 scores (see the announcement for the details https://codeforces.com/blog/entry/62355).

Hi Codeforces.

I am glad to share a small but useful update of Polygon, which was fully developed by me in the walls of ITMO. Now preparing problems with unusual I/O will become a little easier.

Now in the new problems you will get examples in the statements without any transformations by LaTeX/HTML. If earlier you had difficulties with the correct formatting of empty lines or the fact that a double hyphen is replaced with a dash, now there are no such difficulties. The enhancement works for both PDF and HTML statements.

For example, to have such I/O examples just add such a test and use the appropriate output from the model solution.

Note that the feature to overwrite the examples is stayed working (custom content of input or output data for statements). It seems that there are almost no reasons to use it for an input now (apparently, only for interactive problems).

Previously created problems use the old approach, so this innovation should not break existing problems.

How do you like the feature?

Hi Codeforces!

Meet a small innovation on Codeforces — difficulties of problems (and at the same time a new widget filtering problems in the archive). For all the problems of the archive, I’ve calculated the difficulties in the scale of the rating of participants. Approximately this means that if the rating of the problem is equal to yours, then on a typical round you would solve the problem with a probability of 0.5. And, in general, if your rating is r_i, and the problem rating is r_j, then the problem during the round can be solved approximately with probability:

For example, if the rating of a problem is less than yours by 200, then the expected probability of solving the problem is 0.75. With a difference of 400 rating points, the probability increases to 0.9.

For convenient search of problems in the archive, you can now use a special widget:

With it, you can find not only problems that have all the chosen tags, but also which have at least one tag from the list.

A difficulty of a problem is also displayed when choosing problems in a mashup.

I hope that now you will be able to do more effective practice, and the process of making new mashups for trainings will become easier.

UPD 1: Have you already noticed new pop-ups about judgment verdicts of your submissions?

UPD 2: (API update) Optional field rating has been added to the object Problem in API.

Hello!

ACM-ICPC Southern Subregional Contest (NEERC/Northern Eurasia) 2018 has ended on October 16. There were 72 teams onsite in Saratov, most of them were invited because of their result on the qualification stage.

On Oct/20/2018 11:05 (Moscow time) will start online-mirror 2018-2019 ICPC, NEERC, Southern Subregional Contest (Online Mirror, ACM-ICPC Rules, Teams Preferred).

In this contest I play a role of Cheif Judge and the jury teams consists of ex-participants of ICPC from Saratov and jury members from other cities. Many thanks to all of them! I hope you will like the problems!

I invite ACM-ICPC teams and individual participants of Codeforces competitions to take part! Sure, the contest will be unrated.

MikeMirzayanov

Hi Codeforces!

For you, perhaps it was yet another Codeforces round. But not for me. Codeforces Round 515 (Div. 3) is the first round tested on new judging servers at ITMO University. And this is not just an update of location. Ta-dam! Now your solutions will be judged on the new Intel i3-8100 processors. And this is not all news. The number of judging servers has increased, which means fewer queues during rounds!

I am pleased to announce that now I live in St. Petersburg, I work at ITMO, and Codeforces is gradually moving from the walls of dear to me Saratov University to ITMO University. The decision to move was not easy for me. My plan is that, based on ITMO, I can focus more on Codeforces development and work on the platform. The number of world champions per square meter is simply overwhelming, and working with a large team of such enthusiasts (and professionals!) of sports programming, like me, is extremely inspiring. I always liked St. Petersburg and the atmosphere of ITMO. Intuition did not let me down. I feel surrounded by people close to me in spirit (and I’m not only talking about a work). I am sure there are many interesting common projects ahead!

I do not say goodbye to Saratov. This is my hometown, full of people dear to me. I came to my first programming training at SSU exactly 20 years ago. Antonina Fedorova, thank you very much. Natalya Andreeve, I would like to say a personal thank you now. You have opened for me an interesting world of programming competitions. We were happy together when we first advanced to the ICPC Finals, and later when we became champions of Russia and the World. We made countless competitions and helped many Saratov students find themselves in programming. I fervently support the future of the Programming Competitions Training Center at SSU and future generations of Saratov contest participants. And now, I am in Saratov and still the head of the jury of the ICPC Subregional Contest, and even an SSU employee. I hope that we will make a good and interesting contest.

I will try to make a complete relocation of the Codeforces infrastructure to ITMO without downtimes. A good Internet connection between SSU and ITMO is encouraging. All the planned work will adapt to the schedule of the rounds, and now it pleases more than ever (I send my greetings to the coordinators!).

Currently, all Codeforces and Polygon solutions are being judged on new servers based on Intel i3-8100 processors. Fortunately, the performance of a single core is not very different from the one that the old generation of judging servers had. Thus, the time limits in all problems remain the same.

Such news. I am waiting for you on Codeforces Round #516 (by Moscow Team Olympiad).

— MikeMirzayanov