Submitting and judging
How to submit a solution to a programming problem on LCOJ, what happens after you click submit, how to read the results page, and the most common mistakes.
⏱ ~10 minutes · 👤 Students and practice users · 🔑 A signed-in LCOJ account
Before you start
Submitting
- Open the problem page, for example
https://luyencode.net/problem/aplusb. - Pick one of two options:
- Click the Submit solution button in the right-hand info column to open the dedicated submit page (
/problem/<problem code>/submit). - Or scroll to the bottom of the problem page and open the Submit Solution tab to submit in place.
- Click the Submit solution button in the right-hand info column to open the dedicated submit page (
- Choose a language from the dropdown. It only lists languages the problem allows and that an online judge supports. The dropdown also shows compiler versions.
- Put your source code in the editor. You can paste it, pick a file on the Paste your source code here or load it from a file: line, or drag a file onto the editor. The file's contents load into the editor so you can review them before submitting.
- Click Submit!. Your browser goes to the submission page
/submission/<id>, where you follow the results.
File-only languages
Some special languages, such as Scratch (an .sb3 file) or Output Only (a .zip file), have no editor. The submit page shows You can only submit file for this language. with a box to pick or drop a file. The file must have the right extension and stay under the language's size limit.
Submission limits
| Limit | Details |
|---|---|
| Source length | Up to 65536 characters |
| Pending submissions | By default, each user can have at most 2 submissions queued or grading at once. Submitting more shows You submitted too many submissions. Wait for earlier ones to finish, then submit again |
| Contest attempts | Some contests limit how many times you can submit each problem. The remaining count appears right under the submit button |
| Languages | You can only use languages the problem allows. If no judge can grade the problem, the page shows No judge is available for this problem. |
What happens after you submit
In short (the terms judge, bridge and verdict are explained in the Glossary):
- The site saves your submission as Queued and sends a grading request to the bridge.
- The bridge picks a free judge that has the problem's data and supports your language. If every judge is busy, the submission waits in the queue.
- The judge compiles your code. If compilation fails, the submission stops at Compile Error (CE).
- The judge runs each test in a sandbox, measures time and memory, and sends back the result of each test.
- The bridge writes the results to the database and notifies wsevent. The submission page open in your browser receives the update over a WebSocket and refreshes itself, so you don't need to reload.
Reading the submission page
The /submission/<id> page changes as grading progresses:
| You see | Meaning |
|---|---|
| We are waiting for a suitable judge to process your submission... | In the queue (QU) |
| Your submission is being processed... | The judge is compiling (P) |
| Compilation Error with a message | Compile error (CE). Read the message to fix it |
| Compilation Warnings | Compiled with warnings. Grading continues |
| Execution Results and a list of tests | Grading in progress or finished |
Per-test results
Each test gets one line, for example:
Test case #1: Accepted [0.012s, 3.21 MB] (10/10)
Test case #2: Wrong Answer [0.015s, 3.21 MB] (0/10)
Test case #3: Time Limit Exceeded [>1.000s, 3.30 MB] (0/10)| Part | Meaning |
|---|---|
Test case #N | Test number. On batched problems, tests are grouped under Batch #N, and a batch only scores when every test in it passes |
| Result | The verdict name (short codes like AC, WA, TLE), sometimes with short feedback in parentheses. See Status codes for every verdict |
[0.012s, 3.21 MB] | Run time and memory used. For TLE, the time shows as > the limit |
(10/10) | Points earned / maximum points for the test |
Above the list is a row of summary icons: a ✓ for passed tests, an ✗ for failed ones (click to jump to that test), and – for skipped tests.
Test rows with an arrow at the start have extra details; click to expand them. Outside contests, the first few tests may include Judge feedback (for example, a checker explaining what went wrong). If the problem lets you view its test data, you also see the input, the expected answer, and Your output (clipped).
Setters can hide some results
Depending on the problem's settings, the submission page may show results per test, only per batch, or only the overall result. During a running contest, detailed feedback is usually hidden.
Summary
When grading finishes, the bottom of the page shows:
- Resources: the longest run time and the largest memory usage across tests.
- Final score: the total test points, plus the problem points, for example
20/30 (6.667/10 points).
Partial scoring
- On problems with partial scoring, your score is proportional to the test points you earned. Failing a few tests still gets you points.
- On problems without partial scoring, you only score when you pass every test. Failing one test means 0 points for the problem.
Pretests in contests
Some contests only grade against pretests (a small subset of the tests) during the contest. The submission page then says Pretest Execution Results, tests show as Pretest #N, and the score is labeled Final pretest score:. Passing all pretests does not guarantee a full score when the full test set is run after the contest.
Actions on the submission page
| Button / link | What it does |
|---|---|
| View source | See the code you submitted |
| Resubmit | Opens the submit page prefilled with this submission's code and language, so you can edit and submit again. Only on your own submissions |
| Abort | A button under the test list, shown only while grading is unfinished (shortcut: Ctrl+Enter). The submission becomes Aborted (AB) with 0 points |
On the problem page, the right-hand column has My submissions, All submissions (everyone's), and Best submissions links.
Viewing other people's solutions
You can always view your own code. For other people's submissions, LCOJ's default is: visible only after you solve the problem (an AC with full points). Problem setters can change this per problem, letting everyone see solutions or nobody.
Submitting many times doesn't cost you points in practice: only your best score on each problem counts. In contests, scoring and penalties depend on the contest format.
Troubleshooting
| Symptom | Common cause | Fix |
|---|---|---|
WA although it works locally | Printing extra text like Enter n: or The answer is: | Print exactly what the statement asks for. The default checker ignores extra spaces, but not extra text |
WA on large tests, small tests pass | Integer overflow (int only holds up to about 2·10⁹) | Use long long in C/C++ or long in Java when the result or an intermediate product can get large |
WA, IR, or RTE on the first test | Reading/writing files when the problem uses stdin/stdout (or vice versa) | Follow the statement. Remove freopen(...) unless the problem asks for files |
TLE | The algorithm is too slow for the input limits | Estimate complexity: roughly 10⁸ simple operations per second |
TLE with large input or output | Slow I/O: unsynced cin/cout, frequent endl, input() in Python | C++: ios::sync_with_stdio(false); cin.tie(nullptr); and use '\n' instead of endl. Python: sys.stdin.readline, or try PyPy 3 |
TLE with a correct algorithm | An infinite loop, or the program waiting for input that never comes | Check loop exit conditions and read exactly as much input as the problem provides |
RTE (segmentation fault) | Out-of-bounds array access, recursion too deep | Size arrays according to the limits in the statement |
CE in Java | The main class isn't declared public class, or there's a package line | Declare the main class as public class and remove the package line |
CE although the code is fine | Wrong language or version selected (e.g. C++ code submitted as C) | Click Resubmit, pick the right language, and submit |
For every verdict in detail, see Status codes. For the language list, see Supported languages.
Next steps
- Taking part in contests: submitting, pretests and the scoreboard during a contest.
- FAQ: quick answers to other common questions.