High-Level Design
Design an online judge like LeetCode: a user submits source code for a coding problem, the system runs it against a set of hidden test cases under strict limits, and returns a verdict — Accepted, Wrong Answer, Time Limit Exceeded, and so on.
In scope: submitting code and receiving a graded verdict, running submissions against hidden tests under resource limits, and a contest mode with a live leaderboard during a synchronized flood of submissions. Out of scope: the in-browser code editor, problem authoring and curation, discussion forums, and the exact contest-rating algorithm.
What a strong answer sounds like
State the decision, connect it to a requirement, and name the tradeoff. Keep the design focused on the workload in the prompt.
The AI interviewer asks about this part of Design LeetCode (Online Judge). The interviewer guides you through topics one by one.