Users can create their own domains. For example, a teacher can create a domain for a class and add problems and students, or a group can use a domain as a team space.

Roles and permissions determine whether a domain is public or private.

The default domain is system. Visiting Glassbird opens this domain. Clicking the Hydro logo returns to system from any domain.

Each domain has its own independent problem set, discussions, training plans and contests.

Glassbird uses HydroJudge to evaluate submissions. See the status page for compiler versions and compilation options.

The judge measures process CPU time. The time limit is defined by the problem and its test cases.

The memory limit is 256 MiB by default, unless a different limit is specified in the problem or test configuration.

Unless otherwise stated, Glassbird uses standard input and standard output (STD I/O).

• Waiting The submission is waiting to be picked up by a judge.
• Fetched A judge has picked up the submission and is preparing to evaluate it.
• Compiling The program is being compiled.
• Judging Compilation succeeded and the program is being tested.
• Accepted The program produced the correct output.
• Wrong Answer The output differs from the expected answer; trailing spaces and empty lines at the end are ignored by the default checker.
• Time Limit Exceeded The program exceeded the time limit.
• Memory Limit Exceeded The program exceeded the memory limit.
• Runtime Error The program failed during execution, for example due to division by zero, invalid memory access or stack overflow.
• Compile Error The program could not be compiled.
• System Error The judge encountered a system error. Please report it in the discussion area.
• Canceled Judging was canceled.
• Unknown Error An unknown error occurred.
• Ignored The submission was ignored.

A canceled score means an administrator invalidated the record, possibly because of a rules violation such as code that closely matches another submission.

Possible causes include:

• 1. The wrong programming language was selected.
• 2. The main Java class was not named "Main".
• 3. C/C++ compatibility issues; see the notes below.
• 4. A syntax error or another compilation error.

Notes for C/C++ submissions:

• 1. Use long long instead of the non-standard __int64 type in GNU C++.
• 2. The return type of main() must be int, not void.
• 3. A variable declared inside a for-loop initializer is out of scope after the loop.
• 4. itoa is not a standard C/C++ function.
• 5. Check that printf format specifiers match the types of their arguments.

Training plans organize selected problems into learning paths. Open Training in the navigation bar to get started.

Glassbird does not provide an acceptance-ratio statistic.

RP can be earned through problems, activities and contests.

Problem difficulty is estimated algorithmically using submission counts, judging results and submission timing.

Keep the following points in mind:

• 0. A larger difficulty value generally means a harder problem.
• 1. Estimates for new problems may be inaccurate and improve as more submissions are received.
• 2. Earlier submissions have a larger influence on the difficulty estimate.
• 3. Difficulty is an estimate and may not always be accurate.

See the test data configuration documentation.

If you cannot sign in, check that you are using the correct username. You may have added a prefix or suffix when registering because your first choice was already taken.

If your account was compromised or you forgot your username or password, use Reset Password or Find Username.

Hydro uses CommonMark syntax with the following extensions:

• Mathematical formulas using KaTeX syntax.
• Mention a user with @[](/user/uid).
• Highlight text with ==text==.
• Set image dimensions with ![alt](url =100x100).
• Embed a video with @[video](https://.../a.mp4).
• Embed an external video with @[bilibili](BVxxx).
• Embed a PDF with @[pdf](https://.../a.pdf).
• In problems, contests, homework and training plans, reference attachments with file://filename (recommended).
• A subset of HTML tags is supported.