My first submission for problem A in C++ was

ceil(1.0 * n / 2) and got WA. Does anyone have any idea what is wrong?

I don't like the problems which can be done without using functions or loops

Problemsetting might not be the job for you.

It shows the message that "You are not allowed to view the requested page" when trying to access the jury solutions.

Pathetic and Confusing problem statement for problem B. Shitty Contest

Link for the solution codes are not working right now ... please fix them.

Can someone elaborate problem D's editorial?

I think B and C should have been swapped. Thanks for fast editorial though.

I think D was little bit similar to 1360G - A/B Matrix and thank you for a nice contest.

pattern in questions!

I know it's too much to ask from anyone , but i will be highly obliged and grateful to the one who will look at my submissions of D to see why it fails to pass test cases . My submission link : https://codeforces.net/contest/1371/submission/85694260

Could E be solved, under the same constraints, if P was not prime ? I'm curious about it.

Div2 rounds are now tending towards Div3! who else feels same?

Question B should have been better explained

To be honest, felt like a div3. except the last problem. For others, no. of submissions is almost same as on a div3.

In C's editorial shouldn't it be m<=min(a,b) rather than m<min(a,b)?

Why can't someone who knows English go over the problems and correct bad translations? It's so hard to read these problems with so many out of place commas, and completely messy sentences.

Editorial Problem E1 You can find the value of f(x) by the following simulation:

First, let v={the number of enemies they have strictly less than x candies}, ans=1. Then do the following steps for i=x,x+1,...,x+(n−1). v=v + {the number of enemies they have exactly i candies} ans=ans∗v v=v−1

Is it just me or was this part not really that intuitive?

Решения жюри — самый говнистый говнокод который я когда-либо видел.

I did the same thing that's mentioned in the editorial for E1. But I am getting WA for test 5. Submission.

Can someone explain C with examples? And what tags do these types of problems come under?

Finally understood B, thanks!

At least provide some explanation for problem D. We can see the other's submission if we want to see code.

Any reason for making problem C around the same difficulty as a typical Div2 A?

In D there should be either (1^2 + 1^2) or 2 * 1^2, not 2 * (1^2 + 1^2).

problem C was fantastic for me.I spended too much time for it.when I finded it's solution I just surprised.

First 4 problems felt more like div3 contest only maths and implementation kind. Or may be I am improving.

Felt like giving an Aptitude test!

https://codeforces.net/blog/entry/79541?#comment-654173 This single comment has a better explanation for A, B, C than this editorial

Can Any One Explain me Solution of problem:E1? Because I am still not able to understand it through Editorial. Please Explain if You know .

Can someone please help me with this submission for E1. It gets WA on test 9.

EDIT : I found the mistake. I was using set data structure earlier to get the count of elements less than or equal to $$$x+i$$$ which is wrong as it only stores unique elements and thus might give me wrong count values in case of duplicates.

.

how can one arrive to the approach used in problem D. I mean is it really too intuitive? If yes, then can anyone share similar problems for practice.

Shouldn't it be $$$m \le min(a,b)$$$ for problem $$$C$$$?

In E2 for solution 1 :

"if C_i(x) exceeds p, then there will be some C_j(x) = p as C_i(x) decrements by at most 1".

Why is this necessary that some C_j(x) will be equal to p?

what if C_i(x) does not decrease but only increase? Can someone explain?

The problems were wonderful. I loved them all.

However Ruby 2.7.1 (which was upgraded from 2.0.0 recently) is too slow on Codeforces. My O(1) (I mean, O(t)) solutions don't pass! https://codeforces.net/contest/1371/submission/85638755 Same code with same input passes in 150ms on Macbook Air and 75ms on AtCoder!

It seems that any Ruby2.7.1 submission takes 900ms at least. (Even if 1 line do-nothing code) So I guess Ruby2.7.1 on Codeforces has somewhat wrong settings.

And I found that previously passed code makes TLE now with Ruby2.7.1.

• https://codeforces.net/contest/1266/submission/73652966 passed in 171ms previously(Ruby2.0.0)
• https://codeforces.net/contest/1266/submission/85706731 TLE now (Ruby2.7.1)

Please let me know if any better place to report bugs to Codeforces. Thanks!

Shouldn't it be m <= min(a,b) in place of m < min(a,b) as written in the editorial

For all those who want to understand how the solution for D is working, have a look at the comments of my code.

I can't understand the solution of C except the base condition n + m <= a + b. And how to think solution of this kind of problem, I tried different types of conditions but couldn't unite them.

The contest was mostly logic based for question A to E1 and not much related to algorithms and data structures.

In problem E2 (Asterism), after we have calculated b_i, how are we able to find all the "good" x's in linear time?

Your algorithm for comprehending D is funny, Mr physics0523 ;P

For the whole round, I thought that in problem B, we have to count only one pattern for the row that completely divides the total number of days.The problem statement could have been written more clear.

still can't solve C :( if we call type 1 guest before type 2 guest then it won't decrease min(a,b) right? but in editorial

if there is a type 1 guest before a type 2 guest, the type 1 guest have a possibility to decrease the value of min(a,b) unnecessarily

I'm not sure whether this was mentioned before, but there is a DP solution to E1 which generalizes to E2. I am going to present a handwavy explanation of it:

85709850 Here, dp[i] denotes the number of valid permutations of the i smallest elements. From there, we want to insert a new element in these permutations, which does not make any of the existing duels worse, as our candies are monotonically increasing, so we just find the number of positions, where we can put the new element. If we had x candies at start and our new duel is the k-th one, then we will have x + k — 1 candies, so this must be at least the new amount of candies.

Now moving on to E2:85708674

Knowing the recursion from the dp, we can now see that if we have too few candies to win a duel, f(x) is 0, and if we have at least as many candies at start than the p-th smallest enemy, we will also have trouble, because that multiplies our dp by p. So we can find the min and max candies easily, and now we just want to quickly decide whether any of our other products are zero. The parts in the dp product before the p-th smallest element cannot be divisible by p, as they are positive but smaller than p, so we just take the elements from the p-th to the n-th and see whether they give a zero residue with p, granted that we have less candies than them when starting the fights (this follows from the enemies being sorted and us having at less candies than the p-th smallest enemy). This can also be done linearly.

E1, "Yuzu should have at least $$$m-n+1$$$ candies initially to win all duels."

Isn't that wrong? Having that much candis garanties that not all duels get lost, but to garantie to win all duels Yuzu must have $$$m$$$ candies. Since all a[i] can be equal $$$m$$$.

I mean, a[] is not a permutation or somehow else pairwise distinct.

In tutorial of C it should be m <= min(a,b) instead of m < min(a,b) for answer to be "Yes".

The test cases for E1 were such that I got a TLE when I solved in O(n*n*logn). Till today I thought log(n) does not make a difference. Got to learn something from the question.

Why am I getting WA on test case 6 of E1: 85714673

UPD: Fixed it

Can anyone please tell me what is wrong with my code for E1?

https://codeforces.net/contest/1371/submission/85673827

#include<bits/stdc++.h>
 
int main() {
	using namespace std;
	ios_base::sync_with_stdio(false), cin.tie(nullptr);
	int T; cin >> T;
	while (T--) {
		int N, K; cin >> N >> K;
		cout << (K % N == 0 ? 0 : 2) << '\n';
		for (int i = 0; i < N; i++) {
			for (int j = 0; j < N; j++) {
				int d = (j - i + N) % N;
				if (d * N + i < K) {
					cout << '1';
				} else {
					cout << '0';
				}
			}
			cout << '\n';
		}
	}
 
	return 0;
}

This is ecnerwala's solution for Problem D, can somebody help me in understanding how this solution works and what was the intuition behind that :)

This editorial is so hard it needs another editorial. Seriously, it was easier for me to solve problems than to understand this, not even saying anything about jury code quality. Some standards for writing editorials are needed.

binary search solution of E2

Hello, can anyone tell me how long we have to wait to see the change in our rating, system checking is done hours ago

If you prefer video explainations, I go over everything (except a rather handwavey description of E2) at the end of my screencast of the round.

Can anyone please explain how this solution works for 1371E2 - Asterism (Hard Version). Thanks in advance.

        int n, p, a[n];
        cin >> n >> p;
        for (int i = 0; i < n; i++)
            cin >> a[i];
        sort(a, a + n);
        int l = 0, r = 1e9;

        for (int i = 0; i < n; i++)
            l = max(l, a[i] - i);
        for (int i = p - 1; i < n; i++)
            r = min(r, a[i] - i + p - 1); // need help with this part

        cout << max(0, r - l) << endl;
        for (int i = l; i < r; i++)
            cout << i << " ";
        cout << endl;