Managing Problems

LCOJ provides a web interface for creating and editing problems, including both problem statements and test data.

Configuration

With Docker (recommended)

Test data is stored in the dmoj/problems/ directory, which is mounted into the container automatically.

No extra configuration is needed; this is already set up in Docker.

With bare metal

In local_settings.py, set DMOJ_PROBLEM_DATA_ROOT:

DMOJ_PROBLEM_DATA_ROOT = '/home/lcoj/problems'

Adding a New Problem

Step 1: Open the admin site

Go to /admin/ and log in with an admin account.

Step 2: Create the problem

Click the Add button in the Problems section.

Step 3: Fill in the basic information

Required fields:

• Problem code: The problem code (must be unique, e.g. APLUSB)
• Title: The problem name (e.g. "Sum of Two Numbers")
• Authors: Important! You must add yourself as an author, otherwise you will not be able to edit the problem

Step 4: Write the problem statement

LCOJ supports Markdown with extended features:

• LaTeX for math formulas
• Syntax highlighting for code
• Images and tables

Example problem statement:

# Problem

Given two integers $a$ and $b$, compute their sum.

## Input

A single line containing two integers $a$ and $b$ ($-10^9 \le a, b \le 10^9$).

## Output

Print a single integer, $a + b$.

## Example

### Input
```
3 5
```

### Output
```
8
```

## Limits

- Time: 1 second
- Memory: 256 MB

See the full template.

Step 5: Configure the problem

Key options:

• Time limit: Time limit (seconds)
• Memory limit: Memory limit (KB)
• Points: Points for the problem (usually 100)
• Partial: Allow partial points
• Group: Problem group
• Types: Problem types (DP, Graph, Math, ...)
• Allowed languages: Allowed languages

Step 6: Save and view

Click Save, then click View on site to view the problem.

Managing Test Data

Step 1: Open the test data editor

On the problem page, click Edit test data.

Step 2: Upload test data

Prepare a zip file containing the test data. Naming convention:

<problem_code>.<test_number>.in   # Input file
<problem_code>.<test_number>.out  # Output file

Example: For problem APLUSB:

APLUSB.1.in
APLUSB.1.out
APLUSB.2.in
APLUSB.2.out
APLUSB.3.in
APLUSB.3.out

Upload the zip file.

Step 3: Configure test cases

Key fields:

• Input file: Path to the input file inside the zip
• Output file: Path to the output file inside the zip
• Points: Points for the test case

Example configuration:

Test 1: APLUSB.1.in, APLUSB.1.out, 30 points
Test 2: APLUSB.2.in, APLUSB.2.out, 30 points
Test 3: APLUSB.3.in, APLUSB.3.out, 40 points

Scoring

If Partial points is enabled:

Formula:

Score = (Points of passed tests / Points of all tests) × Problem points

Example:

• The problem is worth 100 points
• 3 tests: 1/2/7 points
• A contestant passes tests 1 and 2 and fails test 3
• Score = (1+2)/(1+2+7) × 100 = 30 points

Batched Test Cases

Use these for problems with subtasks. All tests in a subtask must pass to earn its points.

How to create:

1. Click Add batch
2. Set the points for the batch
3. Add test cases to the batch

Example:

Batch 1 (30 points):
  - Test 1.1
  - Test 1.2
  
Batch 2 (70 points):
  - Test 2.1
  - Test 2.2
  - Test 2.3

Custom Checkers

If a problem has multiple correct answers, use a custom checker.

Built-in checkers:

• standard: Exact comparison (default)
• floats: Allows floating-point error
• sorted: Ignores order
• identical: Character-by-character comparison

Choosing a checker:

In the Checker section, select the appropriate checker and configure its parameters.

Generator

If there are many tests, you can use a generator instead of uploading files.

How to use:

1. Upload the generator file (C/C++)
2. Configure the parameters for each test
3. The system generates the input/output automatically

See also: Generator

Test Submission

Once the test data is ready, go back to the problem page and click Submit solution to try a submission.

Updating Test Data

To modify test data:

1. Open Edit test data
2. Upload a new zip file or edit the configuration
3. Click Save
4. The test data is updated automatically

Rejudge

After changing test data, you should rejudge existing submissions:

1. Go to the problem page
2. Click Rejudge all submissions
3. Choose the rejudge scope (all submissions, or from a certain point in time)

Tips

• Name tests clearly: Easier to manage and debug
• Test thoroughly: Include edge cases and corner cases
• Check the outputs: Make sure the expected outputs are correct
• Try multiple languages: Test with C++, Python, and Java
• Read the logs carefully: If something fails, check the logs for the cause

Troubleshooting

Test data does not load:

• Check the file paths inside the zip
• Check the permissions of the DMOJ_PROBLEM_DATA_ROOT directory

Checker does not work:

• Check the checker syntax
• Check the error log in the admin

Rejudge does not run:

• Check that Celery is running (Docker): docker compose ps celery
• View Celery logs (Docker): docker compose logs -f celery
• Check Celery (bare metal): supervisorctl status celery
• View Celery logs (bare metal): supervisorctl tail -f celery