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C++ has always had the convenient data structures std::set and std::map, which are tree data structures whose operations take time. With C++11, we finally received a hash set and hash map in std::unordered_set and std::unordered_map. Unfortunately, I've seen a lot of people on Codeforces get hacked or fail system tests when using these. In this post I'll explain how it's possible to break these da

There's been much controversy lately about the late submission strategy not penalized by scoring systems of AtCoder and CS Academy. Most of the relevant discussion happened earlier at http://codeforces.com/blog/entry/53431 and http://codeforces.com/blog/entry/53449. I have a lot of thoughts on the topic, so I've decided to share them in a separate blog post. I really like the strategic part of pro

As you know, the C++ language assumes that the programmer is always correct. Therefore C++ compilers don't add additional checks to the program, such as checks for null pointer dereference or out-of-bounds array access. This is good, because C++ programs run as fast as possible, and this is bad, because sometimes we may spend a long time debugging some silly mistake. We would want that the compile

C++17 is now available on codeforces, community wants new edition of C++ tricks by HosseinYousefi, so, let's start! Disclaimer: I have done only few examples of new features, which in my opinion are related to competitive programming. Feel free to comment and provide more real-world examples or ask to elaborate some features with more examples or explanations. Fold expressions I think that everybo

This is my first attempt at writing something useful, so your suggestions are welcome. Most participants of programming contests are familiar with segment trees to some degree, especially having read this articles http://codeforces.com/blog/entry/15890, http://e-maxx.ru/algo/segment_tree (Russian only). If you're not — don't go there yet. I advise to read them after this article for the sake of ex

Hi! See this useful C++ include directive. #include <bits/stdc++.h> This let you use any C/C++ standard library without adding extra "includes". No more compilation errors because missing libraries :) And you can make a shorter version of your template. For example, my template. #include <bits/stdc++.h> #define _ ios_base::sync_with_stdio(0);cin.tie(0); using namespace std; int main() { _ return 0

Several recent problems on Codeforces concerned dynamic programming optimization techniques. The following table summarizes methods known to me. Name Original Recurrence Sufficient Condition of Applicability Original Complexity Optimized Complexity Links

On the special day of 1024, I am very glad to invite you to participate in Codeforces Round 1061 (Div. 2), starting at Oct/24/2025 17:35 (Moscow time) There will be six problems for you to solve in two hours, one of which will have two parts. At least one problem will be interactive, so please make sure to read the guide for interactive problem before the contest. This round will be rated for all

Hello, Codeforces! We are happy to invite you to an exciting online event: ICPC 2022 Online Challenge powered by HUAWEI，which will start on September 15, 2022, 00:00 UTC (UTC+0). In this Challenge, you will have a unique chance: to compete for 2 weeks online during the challenge to solve 1 or 2 problems prepared by different business domains of HUAWEI to win amazing prizes from HUAWEI! As a specia