I see blitz matches going to a high level in the near future...Interesting :))

670D2 - Magic Powder - 2 is the difficult version of 670D1 - Magic Powder - 1, but its statement is incomplete.

819A - Mister B and Boring Game has wrong model solution.

Does incorrect problem ratings count as an issue?

1726F - Late For Work (submissions are not allowed)

Submissions are in fact allowed but you will get wrong answer Submissions to this problem are not allowed -- see statement.

936E - Iqea.

The problem can't be seen.

713C - Sonya and Problem Wihtout a Legend: Typo in the title (Wihtout -> Without)

What about weak test cases? For 464E - The Classic Problem, I have a test case on which 284778122 takes > 1 minute locally. I think that for this problem, it's particularly relevant because this problem is often recommended to students for training purposes.

1340E - Nastya and Bees No correct solution.

1000F - One Occurrence — Severely inappropriate time or memory limits

Using the Mo algorithm get time limit exceeded, and the Mo-based solution in the editorial also times out.

Sorry for my poor english

186E - Clever Fat Rat It seems that the judge has some test cases is broken, and it seems like we can't get an AC without writing a mysterious if statement to handle a specific case.

401E - Olympic Games There is no problem statement. I solved it by guesseing the problem statement from https://blog.csdn.net/u013920003/article/details/21084005.

The presence of some "marathon-style problems" that are impossible to solve, and the lack of a setting to hide them, personally reduces the usability for me. However, reporting such problems is not the point of this article, is it?

206D1 - The Beaver's Problem - 3 The download link is broken. (D2 to D10 is the same)

101628K - Know Your Statement Denial of judgement

Not a CF problem, but in this article I wrote, specifically the line:

• Given a sequence $$$A$$$ of length $$$N$$$ and Q queries $$$1 \le i \le j \le N$$$, compute the length of Longest Increasing Subsequence of $$$A[i], A[i + 1], \ldots, A[j]$$$.

If I replace this to the following, by changing "Q queries" to "$$$Q$$$ queries":

• Given a sequence $$$A$$$ of length $$$N$$$ and $$$Q$$$ queries $$$1 \le i \le j \le N$$$, compute the length of Longest Increasing Subsequence of $$$A[i], A[i + 1], \ldots, A[j]$$$.

Then the whole math formatting gets broken. Someone recently messaged me about this issue, which had not occurred when I originally wrote the post.

1740D - Knowledge Cards I posted a blog about it before but it got downvoted and no one cared. Explanation animation is broken

An INSANE nitpick: I think, technically, https://mirror.codeforces.com/contest/2085/problem/A is wrong. "A string a is lexicographically smaller than a string b of the same length, if and only if the following holds: in the first position where a and b differ, the string a has a letter that appears earlier in the alphabet than the corresponding letter in b." "r is universal if and only if r is lexicographically smaller than the reversal of r." I think, mathematically, this means that a palindrome is universal, since it is vacuously true, that any palindrome is lexicographically smaller than itself, by the above definition.

I suggest removing the limits of the problems ratings, for example some problems can be rated 200 and some can be 600 or 800 and some, yes this happened, is rated 0, all of these are being rounded up to 800 which make the 800 reflects many different difficulties which can let it be hard for the absolute beginners, I will not speak too much about the 3500+ problems that some of them are rated 4000+ and one of them is 4700, but I think this will only be important for the top rated users, but it is the same case :)

In many div3 or div4, we see the first 3 problems rated 800 or so, but third one is significantly harder than the first one.

Broken English: 1651C - Fault-tolerant Network

The line just above the input section is wrong.

Statement relies on the statements of another problem (e.g., the harder version's statement is not complete).

I don't remember the detail, but almost all problems of Helvetic Coding Contest 2016 online mirror (teams, unrated) relies on the statements of another problem.

2094G - Chimpanzini Bananini Incorrect statement, or broken English.

The phrase

The first line of the input contains an integer q

should be

The first line of each test case contains an integer q

2045F - Grid Game 3-angle in the input section, $$$1\leq A_1\leq 10^9$$$ should be $$$1\leq A_i\leq 10^9$$$.

1335D - Анти-судоку The link from the statement explaining sudoku is broken (it probably expired after all of these years), I think replacing it with the Wikipedia link should be good enough.

2041A - The Bento Box Adventure

1.simple solution(can be seen right away)

should be a 800 problem(its a 1300 problem)

1547F - Array Stabilization (GCD version) The hyperlink that's supposed to explain GCD redirects to an unrelated news page.

Broken English: 1682D - Circular Spanning Tree

Error is in 2nd line of the statement:

"report that there such tree does not exist"

1078E - Negative Time Summation -- bug in the checker. Details here. I may have fixed it (sorry I don't know how polygon works), but I would like to know for sure (cc maspy)

Problem — 802K statement relies on easier version

upd: I misread the problem.

190E - Контрнаступление solutions which passed during the contest get a TLE now. Maybe some issue with time limits.

Fairly minor but 43B - Letter, 142A - Help Farmer, 101C - Vectors, 27B - Tournament, 14E - Camels, 147B - Smile House, 158D - Ice Sculptures, 26C - Parquet, 102E - Vectors, 48B - Land Lot, 420E - Playing the ball, probably others: English version contains "и" instead of "and". To find more of these you can search "и" site:codeforces.com/problemset -locale=ruon any search engine.

Shouldn't this Problem 706 D2- E. Garden of the Sun be much lower rated (currently 2300)

590C - Three States

wrong grammar in english version at the end of the first paragraph

it was decided that a road between the states should be built to guarantee so that one could any point of any country can be reached from any point of any other State.

239A - Two Bags of Potatoes typo in first paragraph "gerater" -> "greater"

29D - Ant on the Tree, in the second paragraph

He sees that there are n vertexes in the tree

vertexes should be "vertices". (vertexes also might be correct but i never heard or see someone saying vertexes)

https://mirror.codeforces.com/blog/entry/110092

In the tutorial for C the last word was written as enouth instead of enough

All the problems of contest MemSQL Start[c]UP 3.0 — Round 2 (onsite finalists) are broken and don't accept submissions without making mashup .

878B

"..each consisting of $$$k$$$ participants form the same city.." should be "from the same city".

"..determine how many participants have left in the line.." should be "are left".

"The second line contains $$$n$$$ integers $$$a_1, a_2, ..., a_n (1 \leq  a_i  \leq 10^5)$$$, where $$$a_i$$$ is the number of city, person from which must take seat i in the bus." can be phrased a lot better as " where the $$$i$$$-th seat in the bus is taken by a person from city $$$a_i$$$".

1423A - Wakanda Forever, Input section,

$$$N−1$$$ integers $$$A_{i,1}, A_{i,2},\ldots, A_{i,i-1}, A_{i,i+1},\ldots, A_{i,N-1}$$$

$$$A_{i,N-1}$$$ should be $$$A_{i,N}$$$.

Also, it seems there’s an obvious mistake in the judge. 345419243

https://mirror.codeforces.com/contest/2018/problem/F1

It contains a reference to problem D of the same contest. Likewise, F2 and F3 do as well.

1028H - Make Square Denial of judgement

Submission: 348247841

Blackslex and Another RGB Walking

All my submissions for this problem ended with the verdict "Loading presents for flight 1..." ("Delivery failed FL" after some time) .

Even the almost empty one test submission

240 E Road Repairs the sloution sould be directed MST but simple bfs works and you could easily make a test case that would give wrong answer on most of the accepted solutions out there(the output graph is not connected)

2174F - Mosaic Tree

Some hacks for this problem still result in Unexpected verdict (1160229 to 1160235)

1526C1 - Potions (Easy Version)

The statement has error. "will decrease will health" should be "will decrease your health"

830C - Bamboo Partition weak test cases. Solution provided in editorial 28572941 gives different answer compared to my solution 356538530 on the following test:

3 3 
1 1 3

My solution gives $$$2$$$, and other gives $$$1$$$.

If you need generator:

#include <iostream>

using namespace std;

int main() {
    cout << "3 3" << endl;
    cout << "1 1 3" << endl;
}

Submission: 28572941

Expected verdict: Wrong answer

Problem: 1423A This problem "wakanda forever" has broken testing. It's a 3500 rated problem and this code got accepted:

#include <iostream>
using namespace std;

int main() 
{
    int n;
    cin>>n;
    for (int i=0;i<n;i++){
      cout<<i+1<<endl;
    }
    return 0;
}

In some problems, it is not stated whether the outputs YES and NO are case-insensitive (they are).

• 1850H - The Third Letter (2026.01.07)
• 1839C - Insert Zero and Invert Prefix (2026.01.20)
• 1343B - Balanced Array (2026.01.23)

1158A - The Party and Sweets

"g_j is equal exactly to the maximum among values b_1j, b_2j, ... " — seems should be a_ij instead of b_ij

Also in Russian statement used capital "И" right before this part

https://mirror.codeforces.com/contest/1249/problem/D1

This problem is rated 1800. I don't consider myself good or have solved a considerable amount of problems, but atleast good enough to identify that this problem rating doesnt deserve to be more than 1200.

The problem asks us for each point on a number line, if it has more than k segments covering it, we need to remove from them until their count is <= k, only catch is that we want the minimal removals, to achieve that if we sweep from left to right the obvious optimal choice is to always remove the segment which is covering the most from the right, aka the segment with the maximum ending, pretty straightforward.

[problem:802A] in Russian statement: "уже есть книга нужная книга"

In this contest, the inputs are setTestCase-d while the outputs aren't, making HTML broke when you hover your mouse over the inputs.

Задача 80B — Депрессия — условие на русском языке недоступно по ссылке