Low-Level Design Practice
Implement real classes, run them against test cases, and get your design reviewed with AI feedback.
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How it Works
Reading about encapsulation is easy. Writing a class that actually enforces its own rules, and having that judged, is where the learning happens.
Write the actual class
Every problem gives you a class contract and a starter template in the language you choose. You implement it in a full in-browser editor, not in a text box, and your work is saved as you go.
Graded by real test cases
Run checks your code against the worked examples. Submit runs the full hidden set, so a solution that only satisfies the examples does not slip through.
Reviewed on design, not just output
Passing tests is the first gate. An AI reviewer then scores your class against a published rubric covering encapsulation, where the rules live, and structure, with written feedback on each.
What each problem involves
Every problem follows the same four steps.
- 1
Read the contract
Each problem states the exact class, constructor and method signatures the judge will call, alongside the rubric your design is scored against. Nothing about the grading is hidden from you.
- 2
Implement
Write the class in the editor. Hints are there when you are stuck, and the AI tutor asks guiding questions rather than handing over the answer.
- 3
Run
Check your work against the visible examples as often as you like. Runs are not graded and do not touch your history.
- 4
Submit
The full hidden test set runs first. If it passes, the design review runs and scores your class against the rubric. The submission is accepted only when both clear.
The rubric is shown in the problem panel before you write a line of code, so you always know what the design review is looking for.
Frequently asked questions
How is this different from the LLD mock interviews?
The mock interviews are a timed conversation covering requirements, entities and class design before you write anything. These practice problems are focused coding exercises: one class, a clear contract, and automated grading on both correctness and design.
What happens if my tests pass but the design does not?
The submission is not accepted, and the design review tab explains why with a score for each rubric dimension. Your code is still saved, so you can refine the structure and submit again.
Which languages can I use?
Each problem ships starter templates for the languages it supports, and the language picker in the editor lists exactly those. Your choice is remembered across problems.
Is my code saved?
Yes. Your editor content is kept per problem and per language, and every submission is stored in the Submissions tab. You can click any past submission to load that code back into the editor.
Can I get feedback without submitting?
Yes. The Evaluate button runs the same design reviewer on your current code and returns the score and feedback without grading the submission or affecting your history.
Are the practice problems free?
You need an account to run and submit code. Daily run, submit and review limits apply, and AlgoMaster premium raises them.