Stage 1 of 4: Fix the heap tie-break bug
Background. A web crawler keeps a "frontier" — the queue of URLs it hasn't fetched yet. Frontiers are usually priority queues so important URLs come out first, with extra machinery for retries when fetches fail.
frontier.py defines the Frontier priority queue plus a small set
of heap helpers.
The starter has a bug. One test in tests/test_part1_tiebreak.py fails.
Find it and fix it. Don't change the public interface.
Done when Submit goes green.
Constraints
- Python 3.12+ standard library only
- Time limit: 10 seconds per test
- Editable:
frontier.py - Read-only: all
tests/test_*.pyfiles
What comes after stage 1
The next stages open once the tests for the one before them pass. Each raises the bar, the way an interviewer does in the room.
- Stage 2: Implement push and pop.
- Stage 3: Add ready-task selection.
- Stage 4: Retry failed tasks with cooldown.
The files you get
- Yours to edit: frontier.py.
- Read-only: tests/__init__.py.
- Tests you can read and run: tests/test_part1_tiebreak.py. Hidden tests run on Submit.
The round: an agent in the editor
The assistant here works like the one in the interview IDE. It reads your files, runs code and proposes changes, and you accept or reject each one. It doesn't volunteer ideas, so what gets built is what you asked for. Along the way the interviewer asks about your decisions, and at the end the report says what you checked and what you accepted unread.
Frequently asked, briefly answered
Is Crawler Frontier Queue free?
It is a Pro problem. Free plan includes one complete problem, plus the first stage of several more, so you can see how a round works before you pay.
Which company asks something like this?
LinkedIn. It is modelled on LinkedIn's round: AI-enabled coding round in CoderPad: the assistant writes the code into the editor while you direct it and check what it writes.
Do I bring my own AI tool?
No. The assistant is in the editor, same as in the interview IDEs at Meta, Stripe and Amazon. What you choose at Begin is the format: an agent that proposes changes you accept or reject, an answer-only assistant that can't write code, or no assistant at all.
What does the interviewer ask?
4 questions along the way about your own code, and one at the end about the whole session. A weak answer gets one follow up. The answers go into the report, which ends with a hire or no hire verdict.
Start the problem
Sign in and the problem opens where you left it. New here? An account takes a minute to create, and the Pro plan starts at the first stage of this problem.
More like it: every practice problem, how LinkedIn runs its AI round, the AI coding interview guide.