Codeforces vs DMOJ

Codeforces is a programming-contest community and platform where regular contests give participants a way to solve problems and earn skill ratings. The site says it organizes approximately six contests each month, with free participation open to everybody. In contests following Codeforces rules, participants gain points for solving problems quickly and can test other contestants’ solutions through hacks. Ratings use a modified Elo system, and contestants are split into two divisions. The online judge checks submissions against prepared tests and tests suggested through hacks, then returns a verdict. Past contests are available for practice, while the site says learning content and training features are in development. Codeforces also offers an API that returns some data as machine-readable JSON over HTTP. Public data can be requested anonymously; private user data requires an API key. API requests are limited to one every two seconds, and faster calls receive a call-limit error. The service is free and available on web and through an API.

DMOJ is an open-source platform for programming contests and an archive of programming problems. Its archive includes tasks from past CCC, CCO, COCI, IOI and JOI competitions, among other sources, and it runs a monthly open programming competition. Public contests can be hosted at no cost. Contest formats include ICPC, IOI, AtCoder and ECOO, with system testing, hidden scoreboards and virtual participation. Judging supports interactive and signature-graded tasks, runtime data generators, custom output validators, per-language resource limits and scaling to hundreds of judging servers. Problem statements can include Markdown, LaTeX math and figures, syntax highlighting, PDF generation and built-in editorials. DMOJ integrates with Stanford MOSS for plagiarism checking and supports OAuth login, two-factor authentication and fine-grained staff permissions. Documentation is available for self-hosting the site and judge; the installation guide says the site is tested with MySQL and is unlikely to work with other databases. AI use is prohibited in rated contests, and judging resources cannot be used for AI training.