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Codeforces (Russian: Кодфорсес) is a website that hosts competitive programming contests.[1] It is maintained by a group of competitive programmers from ITMO University led by Mikhail Mirzayanov.[2] Since 2013, Codeforces claims to surpass TopCoder in terms of active contestants.[3] As of 2019, it has over 600,000 registered users.[4] On its 15th anniversary, Codeforces had a total of 1,692,402 users with at least one submission.[5] Codeforces along with other similar websites are used by some sport programmers, like Gennady Korotkevich, Petr Mitrichev, Benjamin Qi and Makoto Soejima, and by other programmers interested in furthering their careers.[6][7][8]

Key Information

Overview

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Codeforces is a platform where people generally practice competitive programming[9][10][11][12] and it offers the following features:

  • Short (2-hours) contests, called "Codeforces Rounds", held about once a week[13][14]
  • Educational contests (2-2.5 hours, with 12 hours (24 hours before Round 45) hacking period),[15] held 2-3 times per month;
  • Challenge/hack other contestants' solutions;
  • Solve problems from previous contests for training purposes;
  • "Polygon" feature for creating and testing problems;
  • Social networking through internal public blogs.[citation needed]
Codeforces non-official vectorized main logo.(Without sponsors)

Rating system

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Contestants are rated by a system similar to Elo rating system. There are usually no prizes for winners, though several times a year special contests are held, in which top-performing contestants receive T-shirts. Some bigger contests are hosted on Codeforces base, among them "The Lyft Level 5 Challenge 2018", provided by Lyft[16] or "Microsoft Q# Coding Contest — Summer 2018" provided by Microsoft.[17]

Contestants are divided into ranks based on their ratings. Since May 2018, users with ratings between 1900 and 2099 can be rated in both Div. 1 and Div. 2 contests. At the same time, Div. 3 was created for users rated below 1600. There is also a Div. 4, which is for users rated below 1400.[18]

Rating range Title Division
3000 — 3999+ Legendary Grandmaster 1
2600 — 2999 International Grandmaster 1
2400 — 2599 Grandmaster 1
2300 — 2399 International Master 1
2100 — 2299 Master 1
1900 — 2099 Candidate Master 1/2
1600 — 1899 Expert 2
1400 — 1599 Specialist 2/3
1200 — 1399 Pupil 2/3/4
≤ 1199 Newbie 2/3/4

History

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Codeforces was created by a group of competitive programmers from Saratov State University led by Mike Mirzayanov. It was originally created for those interested in solving tasks and taking part in competitions.[2] The first Codeforces Round was held on February 19, 2010 with 175 participants. As of the end of November 2025, over 1000 rounds were held, with over 11000 registered competitors per round on average.[citation needed] Before 2012, Codeforces Rounds were titled "Codeforces Beta Rounds" to indicate that the system was still under development.[citation needed]

Academic use

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Codeforces is recommended by many universities.[19][20] According to Daniel Sleator, professor of Computer Science at Carnegie Mellon University, competitive programming is valuable in computer science education, because competitors learn to adapt classic algorithms to new problems, thereby improving their understanding of algorithmic concepts. He has used Codeforces problems in his class, 15-295: Competition Programming and Problem Solving.[21] At the National University of Singapore, Codeforces rating is also used as an entrance qualifying criterion for registering for a 4-unit course, CS3233 Competitive Programming, as students have to achieve a rating of at least 1559 to be able to register for the course.[22]

See also

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References

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External sources

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Codeforces

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from Grokipedia
Codeforces is an online platform dedicated to , offering regular contests, a vast problemset for practice, and tools for community engagement among programmers worldwide. Founded in January 2010 by Mikhail Mirzayanov, a competitive programmer and entrepreneur, it began as a means to enrich the experiences of enthusiasts through structured challenges and social features. The site quickly grew into a central hub for the global community, emphasizing skill development via timed rounds that test problem-solving under pressure. Key features include a diverse array of rated contests divided by participant skill levels, such as Div. 1 for experts, Div. 2 for intermediates, Div. 3 and Div. 4 for beginners, and occasional Global Rounds open to all. These events typically involve solving 4–8 algorithmic problems within 2 to 5 hours, with problems ranging from basic implementation to advanced topics like dynamic programming, , and interactive challenges. Participants receive Elo-based ratings that reflect their performance, fostering a competitive environment where top performers—often from international teams preparing for events like the (IOI) or (ICPC)—gain recognition. The platform also maintains an extensive problem archive, editorial solutions, and a system for discussions, allowing users to upvote content, share insights, and collaborate on contest preparation. Owned and operated by Mikhail Mirzayanov as an individual entrepreneur based in , , Codeforces has evolved to support educational initiatives, including courses and virtual participation options to broaden accessibility. By its fifth anniversary in 2015, it had established itself as a vital resource for training and motivation in the field, with ongoing expansions like the introduction of communication-based problems in rated rounds as recently as November 2025. This focus on quality contests and community-driven content has made it indispensable for aspiring and professional programmers seeking to hone their abilities in a structured, feedback-rich setting.

Platform Overview

Introduction

Codeforces is an online platform dedicated to hosting contests, founded in 2010 by Mikhail Mirzayanov. It operates as an individual entrepreneurship under Mirzayanov, providing a space for programmers to engage in algorithmic challenges and skill development. The primary purpose of Codeforces is to host regular programming contests that encourage participants worldwide to hone their problem-solving abilities through timed challenges. Users register on the platform, where they tackle problems by writing code in supported languages such as C++, Java, and Python, submitting solutions within strict time limits. An automated judging system then verifies the correctness and efficiency of these submissions against predefined test cases. As of 2024, Codeforces boasts over 1 million registered users, with individual contests drawing thousands of participants from across the globe. The platform receives sponsorships from various organizations for specific events and rounds, integrating it into a broader ecosystem of resources.

Core Features

The Codeforces platform offers a comprehensive problemset that serves as a vast archive of problems drawn from past contests, educational rounds, and other events. Problems are rated by difficulty on a scale from 800 to 3500, allowing users to filter and search based on rating, tags such as dynamic programming, , or binary search, and origin contest. This searchable and filterable repository enables targeted practice, with options to view problem statements, submit solutions, and access editorial solutions after attempting them. The section provides a dedicated environment for users to simulate contest conditions outside of live events. It includes virtual participation in past contests, user-created , and mashups of problems for customized practice sessions, supporting both individual and modes with participants from historical standings. Users can filter Gym contests by difficulty, type (e.g., official ACM-ICPC mirrors), and start time, facilitating focused skill development without affecting official ratings. Codeforces features a robust blog system for user-generated content, where participants share tutorials, solution explanations, contest announcements, and discussions on algorithmic topics. Integrated commenting allows threaded replies, fostering community interaction similar to a forum, with features like voting on posts and notifications for updates. This ecosystem encourages knowledge sharing, with high-rated users often contributing in-depth guides on advanced techniques. The platform exposes a public API that enables programmatic access to problems, user submissions, contest standings, and other data in JSON format, supporting methods like retrieving problem details or user ratings. This facilitates integrations with third-party tools, such as IDE plugins for direct submission from editors like Visual Studio Code or mobile apps for on-the-go practice tracking. Developers can authenticate requests for personalized data, enhancing automation for analytics and custom training workflows. Codeforces supports more than 20 programming languages, including C++, Java, Python 3, C#, Pascal, Ruby, PHP, Haskell, and JavaScript, with compilers updated to recent versions for compatibility. The judging system automatically tests submissions against multiple test cases, issuing verdicts such as Accepted for correct solutions, Wrong Answer for incorrect outputs, Time Limit Exceeded for runtime overruns, and Memory Limit Exceeded for excessive resource use, providing immediate feedback on failures. Detailed logs, including runtime and memory usage, are available post-submission to aid debugging. User profiles on Codeforces centralize personal achievements, displaying current rating, participation , a list of solved problems with tags, and virtual results for unofficial practice. Profiles also include customizable elements like avatars and friend lists, along with statistics on submission success rates and language preferences, offering a snapshot of progress without impacting official standings.

Contests and Participation

Contest Formats

Codeforces hosts a variety of formats designed to cater to different skill levels and objectives, ranging from beginner-friendly educational events to high-stakes global competitions. These emphasize algorithmic problem-solving under time constraints, with problems typically involving , structures, and optimization techniques. All formats adhere to standard submission guidelines, including per-problem time limits of 1-3 seconds and limits of 256-512 MB, as specified in individual problem statements. Submissions incur deductions for late submissions or multiple attempts. Educational Rounds are frequent contests aimed at and intermediate participants, held approximately bi-weekly to provide regular practice opportunities. These rounds feature simpler problems drawn from classical topics, with formal statements and exercises to enhance conceptual understanding, and are prepared by external setters such as the Saratov State University team. Lasting 1.5-2.5 hours, they include around 5-6 problems of equal value, rated only for participants below 2100 rating, and conclude with a 12-hour open hacking phase where anyone can challenge solutions without point rewards. Divisional Rounds represent the core of Codeforces competitions, divided by skill level into Division 1 for experts (typically rated 1900+) and Division 2 for novices (rated below 2100). These standard events, often combined as Div. 1 + Div. 2 with separate standings, last 2 hours and feature 5-7 problems per division, with variable point values decreasing over time. Submissions occur in real-time, with hacking available during the contest in a "room" system after locking solutions, awarding +100 points for successful hacks and -50 for failures. Global Rounds are open to all participants regardless of rating, occurring approximately once per month and sponsored by companies to attract a broad audience. These contests follow a format similar to combined Div. 1 + Div. 2 rounds, with 5-6 harder problems over 2 hours, emphasizing advanced algorithms and often including larger prize pools to incentivize top performances. Real-time standings are maintained, with during-contest hacking mechanics identical to divisional rounds. Special events add variety through themed or tournament-style contests, such as the annual Contest, which features humorous, unconventional problems in a joke format using ACM ICPC rules (no hacking, standings by solved problems and penalty time). Another example is the multi-stage Codeforces Blitz Cup, held in 2025 to celebrate the platform's 15th anniversary, involving qualification and final rounds with cash prizes. In November 2025, Codeforces introduced communication problems in rated rounds, a new format where multiple interacting programs solve tasks collaboratively. Standings in all formats are updated in real-time during the contest based on preliminary tests, with final results determined after and any applicable hacking phase. For Div. 1-focused elements in mixed rounds, a post-contest hacking phase may apply to challenge solutions, ensuring solution integrity without during-contest disruptions.

Divisions and Rules

Codeforces contests are structured into divisions based on participants' ratings to ensure fair competition and appropriate difficulty levels. Division 1 (Div. 1) is designated for experienced contestants with a rating of 1900 or higher, featuring more challenging problems that test advanced algorithmic skills. Division 2 (Div. 2) targets participants with ratings below 2100, offering problems suitable for intermediate to advanced beginners, and is rated only for those under this threshold to prevent rating among higher-rated users. Lower-rated contestants often participate in combined Division 3 (Div. 3) and Division 4 (Div. 4) rounds, where Div. 3 is rated for ratings under 1600 and Div. 4 for under 1400; these divisions include easier problems to accommodate newcomers and promote skill development. Promotion to higher divisions occurs organically through strong performances that increase a participant's rating, allowing access to more competitive events without formal application processes. Eligibility for Codeforces contests is broadly open to all registered users worldwide, requiring only a free account creation via or , with no entry fees or preliminary qualifications for standard rounds. However, certain specialized contests, such as or regional events, impose restrictions based on age, country of residence, or student status to maintain fairness and comply with educational guidelines—for instance, contests may limit participation to individuals under 18 or enrolled in specific institutions. All participants must adhere to the platform's terms, including verification of unique accounts, as multiple registrations are prohibited and can result in disqualification. Contest rules emphasize integrity and technical constraints to foster a fair environment. Anti-cheating measures include strict prohibitions on using external assistance, copying code, or maintaining multiple accounts, enforced through automated monitoring of submission patterns and IP addresses to detect unusual activity like simultaneous logins from the same location. detection tools, similar to those used in academic settings, analyze code similarities across submissions to identify copied solutions, leading to penalties such as rating deductions or bans. There are no formal code length restrictions, though practical limits around 64 KB apply due to server constraints, encouraging efficient implementations without excessive boilerplate. Participants must submit solutions in supported languages like C++, Java, or Python, using standard input/output, and are expected to avoid disruptive behaviors such as site overload attempts. Participation occurs in two primary modes: official contests, where submissions during the active period affect the participant's rating and contribute to official standings, and virtual or out-of-contest modes, which allow on past or ongoing rounds without impacting ratings, ideal for skill-building without competitive pressure. Upsolving enables contestants to submit solutions to unsolved problems after the contest ends, typically within a 12-hour window for certain rounds like educational ones, with successful attempts recorded on the user's profile for personal tracking but excluded from official results and ratings. Top performers in Codeforces contests are rewarded to recognize excellence and encourage participation. Common prizes include branded T-shirts for the top 30 finishers in rounds like Global Rounds. Sponsored or special events often feature cash awards ranging from several hundred to thousands of dollars for top finishers. For certain contest series, top performers may receive certificates as formal acknowledgments.

Rating System

Mechanics and Calculation

The Codeforces rating system is based on a modified version of the , adapted for multi-player programming contests where performance is measured by final standings rather than pairwise outcomes. Since the October 2015 update, the system uses a more sophisticated approach to compute rating changes, aiming to reduce while rewarding performance relative to expectations. New users begin with an effective rating of 1400 for calculation purposes, though their displayed rating starts at 0 and increases provisionally over their first six contests (by +500, +350, +250, +150, +100, +50) to reflect performance while accounting for uncertainty, stabilizing near 1400 thereafter. For each participant i with pre-contest rating rir_i, the expected rank () is calculated as 1 plus the sum over all other participants j of the probability that i outperforms j, using the logistic : P(i>j)=11+10(rj−ri)/400P(i > j) = \frac{1}{1 + 10^{(r_j - r_i)/400}} After the contest, let actual be the participant's rank in the official standings (1 is best). To determine the new rating, the system performs a binary search to find a target rating R such that the expected rank computed using R (as if it were the pre-contest rating) approximately equals the mi=actual×seedm_i = \sqrt{\text{actual} \times \text{seed}}
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