How can it be? Is he alien or something? I really want to see his screencast.

I see there are some accounts which shows their Facebook. But I can't find where to do it in Settings. Anyone knows how to do it?

I have setted a problem on Polygon for my private group. Its statement has 2 languages: Vietnamese and English. However, when I open my problem on Codeforces, I cannot find the way to change the problem statement to Vietnamese (English is default). Can anyone help me? Thank you in advance.

Fun fact: this eugalt guy always try to shorten his code

Hello, Codeforces!

Currently, there are many blogs about how to be good at programming, their practice methods are super useful. Today I will write oppositely, I will show you ways to be bad at programming. I guarantee, if you follow what I will mention below, you will be bad forever, to the point of not being able to get better :)

P/s: -Original post- Don't downvote it :( I just write for fun

1. Spend as little time as possible

"Dilligence in place of intelligence". If you spend half an hour improving your programming skill, you cannot be bad. Instead, you should spend time doing other stuff like surfing Facebook or playing games. In case you have nothing to do, you would better go to sleep. One more thing to keep in mind, don't enter the programming forums, don't subscribe YouTube channels or reading blogs about programmings, because if you do that, you will be easy to gain knowledge and cannot be bad.

2. Despise elementary knowledge

Don't learn elementary knowledge like binary search or sorting algorithms or simple data structures. Those things are basis of being a good programmer in near future. So if you hear someone says you have to learn these basic algorithms, don't follow them, if you don't want to be good.

3. Don't follow to the forebears' advice

The forebears like your teachers, brothers, sisters or friends, ... are those who have had practical experience, they know how to learn programming well. If they give you advice, just do the opposite :) or at least ignore it, I swear you won't be able to make any progress in learning programming.

4. Learning theories is always enough

"Learning with practice", that's might be the only way to develop skills, so don't practice. Solving problems will help you to be good in no time. So don't do that, theories are more than enough, or you don't even need to learn theories if you want to become the most stupid person.

5. Don't find free courses on the Internet

Nowadays, it is not hard to find a free course with high quality on the Internet. Don't search keywords like "Elementary C++ programming" or "Basic data structures", etc... if you don't want to be better.

6. Don't be proactive

If you encounter a difficult problem, don't spend time thinking, just ask your friends or searching for tutorial. In short, you shouldn't be proactive, don't think before asking.

7. Don't learn English

If you notice, the most quality documents about technology or programming is mainly written in English. In addition, if you learn English well, you will be exposed to an extremely rich and diverse source of materials, which will make you have more knowledge instead of being ignorant about programming.

8. Don't have passion

After all, if you are passionate, you will be a good programmer in short time. So keep in mind, if you want to be ignorant about programming, absolutely don't have passion on it. If you are forced to learn programming, for example, programming is a compulsory subject on your school, you should only learn to pass the exam, or ask someone to do homework for you.

Conclusion

Those are some of the problems that I thing are the most important if you want to be bad at programming. So how to be GOOD? Simply, just do the opposite of what I mentioned above, or at least avoid doing those things.

Have fun! :)

UPD: Why so many downvotes? I just write for fun. Don't take it seriously. :(

I have no intention to blame Codeforces admins for fixing the server that long because I believe they've tried their best anyway.

I'm in Vietnam, my time zone is UTC+7, that means Codeforces server maintained from 6:30 AM yesterday to today (now is 12:30 AM in my time zone).

So sad... :'(

P/s: Sorry for my weak English.

Statement

Given $$$n$$$ strings. Find the string $$$s$$$ with minimum length such that each of $$$n$$$ given strings is a substring of $$$s$$$.

Constraint

$$$n \le 50$$$

Every of $$$n$$$ strings has length not exceed $$$10$$$

Example:

Input:

3
ab
ba
abb

Output:

abba

This problem is hard for me. Can you give me a hint? Thank you in advance.

Problem source

104168D2 - Nested Sum (Hard Version)

Statement

Given an array of $$$n$$$ positive integers $$$a_{1}, a_{2},...,a_{n}$$$, find the value of $$$\sum_{i=1}^{n}\sum_{j=i+1}^{n}\sum_{k=j+1}^{n}a_{i}a_{j}a_{k}$$$ modulo $$$10^{9}+7$$$

Input

The first line of input contains an integer $$$t$$$ ($$$1 \le t \le 10^{4}$$$).

The first line of each test case contains an integer $$$n$$$ ($$$1 \le t \le 10^{5}$$$), the size of the array.

The second line of each test case contains $$$n$$$ integers $$$a_{1}, a_{2},...,a_{n}$$$ ($$$1 \le t \le 10^{9}$$$), the elements of the array.

The sum of n over all test cases doesn't exceed $$$5\cdot 10^{5}$$$.

Output

For each test case output one line containing one integer, the sum described in the problem modulo $$$10^{9}+7$$$

Example

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

1
50
225

What I've done

I have tried to solve this problem for an hour but when I submit it, many testcase is WA:

Test 1: OK, 0 point(s)
Group G1: 0.0 point(s)
    Test 2: WRONG_ANSWER
    Test 3: WRONG_ANSWER
    Test 4: WRONG_ANSWER
    Test 5: WRONG_ANSWER
    Test 6: WRONG_ANSWER
    Test 7: WRONG_ANSWER
    Test 8: WRONG_ANSWER
    Test 9: WRONG_ANSWER
    Test 10: WRONG_ANSWER
    Test 11: WRONG_ANSWER
    Test 12: WRONG_ANSWER
    Test 13: WRONG_ANSWER
    Test 14: WRONG_ANSWER
    Test 15: WRONG_ANSWER
    Test 16: WRONG_ANSWER
    Test 17: WRONG_ANSWER
    Test 18: WRONG_ANSWER
    Test 19: WRONG_ANSWER
    Test 20: WRONG_ANSWER
    Test 21: WRONG_ANSWER
    Test 22: WRONG_ANSWER
    Test 23: WRONG_ANSWER
    Test 24: WRONG_ANSWER
    Test 25: WRONG_ANSWER
    Test 26: WRONG_ANSWER
    Test 27: WRONG_ANSWER
    Test 28: WRONG_ANSWER
    Test 29: WRONG_ANSWER
    Test 30: WRONG_ANSWER
    Test 31: WRONG_ANSWER
Group G2: 0.0 point(s)
    Test 32: WRONG_ANSWER
    Test 33: WRONG_ANSWER
    Test 34: WRONG_ANSWER
    Test 35: WRONG_ANSWER
    Test 36: WRONG_ANSWER
    Test 37: WRONG_ANSWER
    Test 38: WRONG_ANSWER
    Test 39: WRONG_ANSWER
    Test 40: WRONG_ANSWER
    Test 41: WRONG_ANSWER
    Test 42: WRONG_ANSWER
    Test 43: WRONG_ANSWER
    Test 44: WRONG_ANSWER
    Test 45: WRONG_ANSWER
    Test 46: WRONG_ANSWER
    Test 47: WRONG_ANSWER
    Test 48: WRONG_ANSWER
    Test 49: WRONG_ANSWER
    Test 50: WRONG_ANSWER
    Test 51: WRONG_ANSWER
    Test 52: WRONG_ANSWER
    Test 53: WRONG_ANSWER
    Test 54: WRONG_ANSWER
    Test 55: WRONG_ANSWER
    Test 56: WRONG_ANSWER
    Test 57: WRONG_ANSWER
    Test 58: WRONG_ANSWER
    Test 59: WRONG_ANSWER
    Test 60: WRONG_ANSWER
    Test 61: WRONG_ANSWER
    Test 62: WRONG_ANSWER
    Test 63: WRONG_ANSWER
    Test 64: WRONG_ANSWER
    Test 65: WRONG_ANSWER
    Test 66: WRONG_ANSWER
    Test 67: WRONG_ANSWER
    Test 68: WRONG_ANSWER
    Test 69: WRONG_ANSWER
    Test 70: WRONG_ANSWER
    Test 71: WRONG_ANSWER
    Test 72: WRONG_ANSWER
    Test 73: WRONG_ANSWER
    Test 74: WRONG_ANSWER
    Test 75: WRONG_ANSWER
    Test 76: WRONG_ANSWER
    Test 77: WRONG_ANSWER
    Test 78: WRONG_ANSWER
    Test 79: WRONG_ANSWER
    Test 80: WRONG_ANSWER
    Test 81: WRONG_ANSWER
    Test 82: OK
    Test 83: OK
    Test 84: OK
    Test 85: OK
    Test 86: OK
    Test 87: OK
    Test 88: OK
    Test 89: OK
    Test 90: OK
    Test 91: OK
    Test 92: OK
    Test 93: OK
    Test 94: OK
    Test 95: OK
    Test 96: OK
    Test 97: OK
    Test 98: OK
    Test 99: OK
    Test 100: OK
    Test 101: OK

=
Points: 0.0

I don't know why my code failed, can you find out my mistake? This is my code.

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define fastio ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)
#define multitest int _T; cin >> _T; while (_T--)

const int MOD = 1000000007;

int add(int x, int y)
{
    return (x + y) % MOD;
}

int mul(int x, int y)
{
    return (x * y) % MOD;
}

void solve()
{
    int n;
    cin >> n;

    int a[n];
    int pre1[n+1];
    pre1[0] = 0;

    for (int i = 0; i < n; ++i)
    {
        cin >> a[i];
        pre1[i+1] = add(a[i], pre1[i]);
    }

    int pre2[n-1];
    pre2[0] = 0;
    for (int i = 1; i < n-1; ++i)
        pre2[i] = add(pre2[i-1], mul(a[i], pre1[n] - pre1[i+1]));

    int ans = 0;
    for (int i = 0; i < n-2; ++i)
        ans += mul(a[i], pre2[n-2] - pre2[i]);

    cout << ans << endl;
}

signed main()
{
    fastio;
    multitest
        solve();
}

Thank you in advance ❤️

How could this guy submit B and G2, C and G1 at the same time?

I have got 105 unsuccessful hacking attempt now ;) will I lose any point in this hacking phase? Thank you in advance.

I wonder what will happen if I successfully hack my own solution in a 12-hour hacking phase in Div.3, Div.4 or Educational rounds after seeing this!

I think we should have a "Difficulty" column besides the "Problem" column so that we can see the average difficulty of the problems a person solves. (Sorry for my poor English)