Good luck to all! Happy decisions! Hope everyone enjoys this round! Thanks: adedalic, BledDest, Neon for the assignments and MikeMirzayanov for system Codeforces!

awoo ORZ!

Good luck everyone!

This is where I first became interested in hacking a solution. And why do we need such hacks? Won't this spoil the evening for someone whose solution was hacked?

hope to be specialist again.

Hope to get a positive delta

Hoping for the round to go well

Can I have more points if I hacked other people's solutions?

Spartans!!! it's time to conquer CYAN.

How did people see their expected delta changes? I can only see the status of the problems in the standings.

I seem to getting logged out and am getting timed out errors while trying to access codeforces , is it just me?

I smell unrated round.

Site is not working properly please look into the matter.

Slowforces

Server problem again?

Thanks for making the contest unrated

Contests has been crashing for past several rounds. Please fix this and make this contest unrated.

site couldn't be reached for around 15minutes :')

The contests have been crashing for several rounds. please fix this and make last contest unrated.

Having crashed for 30 minutes, it should be unrated!

Extension? This has to be unrated right.

WORST CONTEST I HAVE EVER SEEN!

nice joke

"Problem D is under investigation." What's that mean?

why these days the rounds are too much unbalanced? MikeMirzayanov

Bro just dropped worst contest in CF history and thought we wouldn't notice :skull:

Server problem and investigation? Should be unrated.

unratedforces :(

My first time getting expert and it's unrated :(

Question B was a joke for some and some were joke for question b

Educational round should be tested!!!!!!!!!

Ladies and gentleman, I present to you, the REAL april fools contest :D

Very poor unexpected!!!!

First time I cannot solve problem B in an Educational Codeforces round. Too hard!

Me having a good contest :)

CF- Let's make it unrated

Bruh, new contests are in the review queue for around 5-6 months, and yet you fail to find if there's an error in a question. I can't comprehend how bad the "testing" process must be!

What is happening!!!

I was going to be specialist today...

I hate robots.

Never been so sad to know the round is unrated when I solve A, B and C in just 30 minutes

I'm sure that I'll see blue after this contest and it just...

Look at the fact that only 1.6k Accepted solutions of problem B. I have never seen this in an Educational round

I thought I could get to Expert but this one is NON-rated now.

Those of you downvoting announcement/making snarky remarks in the comments, please stop. I can't believe I have to say this, but don't you think the authors already feel bad enough about the mistake? It's not like issues with the round (besides technical issues) happen often.

Just because you have a right to complain doesn't mean you should.

Feeling very dishonoured by not able to solve D

Auto comment: topic has been updated by awoo (previous revision, new revision, compare).

Looks like its a even odd pattern going on solve counts.

Untested EduForces!!

This is the first time I haven't worked out question B(For 2023).

I'm a little nervous.

But I like this feeling!

Bon Appetit 2.0

This competition had one official technical issue and one technical issue from the organizer... It ruined the first three very interesting questions. I feel very angry.

I think MikeMirzayanov should make some Duckworth–Lewis–Stern method on codeforces for such round.

Imagine getting DDOS attack but making round unrated for investigation of a problem.

have you ever tested this round...?

I thought I could become an Expert until I found that this round will be unrated

B is so hard for me!

I hate B -_-

it is a really bad experience.the difficulty order of the questions is unreasonable, Bad server ,and unrated.

Unrated because of issues that affected less than 200 people?

Are you joking? It's not my mistake!Why should I suffer the consequences? `

Now that it is unrated, would you please post the editorial ASAP?

No comment starting with as a tester..., maybe this round has no tester?

good contest and problems, love from codeforces

Any idea on how to solve F?

Very nice problem E, satisfying to solve. Such a pity that round got unrated.

How to solve $$$D$$$, and what happened with it?

[deleted]

How to do B? God I've never been stuck at B like this before.

There are issues with problem D in the author's solutions even now. My hack got "Unexpected verdict".

I did binary search for B, but got wa. How to solve B?

B solution: we know that we would never need to increase more than S = 2 * sqrt(max(a,b)) times. We can now try out each max increase from 1 to S. Each time we go from S and reduce the maximum possible for each a and b. This will be done in log(n) times.

https://mirror.codeforces.com/contest/1814/submission/201083355

D solution: We know that we can always get a result at LCM(f1, f2, ..., fn) and the difference will be 0, and we would have to change all of di in this case. If we decide not to change all of di then at least one of them will be fixed. This can be tested by iterating at each ith and pretending we are fixing ith and try out every other di as at either the lower end or the upper end, Then compute the minimum number of changes fro every other positions. Complexity: f * k

A: If k is even, we can pay only even rubles. Otherwise, we can pay even rubles or all prices >=k.

B: Unbalanced problem. If the length of leg is increased t times, we need ceil(x/(t+1)) steps for moving along x-axis, and ceil(y/(t+1)) steps for moving along y-axis, so answer is t+ceil(x/(t+1))+ceil(y/(t+1)). If there's no ceil function, by the basic inequality (a+b>=2*sqrt(a*b)) the answer is sqrt(x+y)-1 and optimal t is around sqrt(x+y). So I passed this problem by brute force for t in range [sqrt(a+b)-1000, sqrt(a+b)+1000]. Also we can use sqrt-decomposition to solve in O(sqrt(a)+sqrt(b)).

C: The cost for first robot is s1, 2*s1, ..., k*s1 for each position, and for second robot is s2, 2*s2, ..., (n-k)*s2. To choose k we can let k=n first, and reduce k by 1 while (k*s1) > (n-k+1)*s2. After decide k we can arrange r[i] by the reverse order of the cost of positions.

D: No idea.

E: By some small test cases we can guess that we need to fill the path by some blocks of size 1 or 2, and the size of blanks between each pair of adjacent blocks is 1 (that's because we need to make something like (i, i+1) --> (i+1, i) or (i, i+1, i+2) --> (i+1, i+2, i)), and the answer is 2*(sum of weight of edges in these blocks). If from each range [l, r] we set siz=r-l+1, start=a[l], end=a[r], ans[i][j]=the answer of problem on range [l+i, r-j] (here 0<=i<=2, 0<=j<=2), we can solve the problem by segment tree.

As a !tester, I'm proud to !be one.

How to solve F? I tried offline dynamic connectivity but don't know how to update the accessibility of vertices.

Do anyone know how to solve B? I didn't participate, but just looked at it, and it seemed interesting. My first thought was that if you can, you always want to increase the leg length up til its sqrt the distance you have to walk. So you look at the biggest square less or equal to x, and same for y. Then you subtract those two squares from x any y. Then you do the same process, all the way down. Keeping track of these squares you know when you have to move, and when you have to increase legs. Is this correct?

Problem B wa3 because I break when answer is greater than last answer.

void solve()
{
  int t = read<int>();
  while(t--) {
    ll x = read(), y = read();
    ll mx = x + y;
    for(ll i = 1; i <= 50000; i++) {
      ll cur1 = (x + (i-1)) / i;
      ll cur2 = (y + (i-1)) / i;
      if(cur1 + cur2 + i-1 < mx) mx = cur1 + cur2 + i-1;
      if(cur1 + cur2 + i-1 > mx) break; // what's wrong
    }
    outl();
    outl(mx);
  }
}

Then I printed all answer, and found that although the answer curve "looks like" go down and go up, but sometimes $$$ans(i) = ans(i-1) + 1$$$ while the curve is "going down"!

It is really sad to see my verdict of D changed from Accepted to Wrong Answer. Althougt my solution is actually wrong.

Task E was very cute

First time to become orange. But unrated.

I think it's funny my first sqrt decomposition solution was for a problem B. Not sure if it's correct though or testcases are just weak. The problems were interesting, maybe just a little unbalanced. Shame this round had so many technical difficulties.

One solution for B:

Given the final leg length $$$m$$$, the result is $$$ceil(\frac{a}{m}) + ceil(\frac{b}{m}) + m - 1$$$. How to find $$$m$$$? Intuitively we want to search around $$$\sqrt{a+b}$$$, but the ceiling makes things complicated. Using the relationship $$$ceil(\frac{a}{m}) + ceil(\frac{b}{m}) \in [\frac{a+b}{m}, \frac{a+b}{m} + 2)$$$, we find $$$m$$$ such that $$$\frac{a+b}{m} + m - 1 < 2\sqrt{a+b} + 1$$$, so the safe search range for $$$m$$$ is $$$(\sqrt{a+b} + 1 - \sqrt{1 + 2 \sqrt{a + b}}, \sqrt{a+b} + 1 + \sqrt{1 + 2 \sqrt{a + b}})$$$, so time complexity is $$$O((a+b)^{1/4})$$$. solution.

Additionally, we can use sqrt decomposition to reduce this to $$$O((a+b)^{1/8})$$$. The execution time is actually slower because of more operations. solution.