Stage 1 of 4: Fix the brute force
Background. A list of words is given. Some of them contain another word from the same list as a contiguous substring: in ["programming", "am", "pro"], programming contains both of the others. container.py holds a brute-force find_containing(words) that is supposed to return those words, and bench.py can time it on the corpora under data/.
The brute force is wrong. Every test in tests/test_part1_brute_force.py fails; the docstring on find_containing says what the result has to be.
Fix find_containing. Keep its shape. Be ready to say what the brute force costs in time and space: the assistant will happily print a complexity, but the interviewer wants yours.
Done when Submit goes green.
Constraints
- Python 3.12+ standard library only
- Time limit: 6 seconds per test
- Editable:
container.py - Read-only:
bench.py,data/*.txt, alltests/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: Fast on the medium corpus.
- Stage 3: Fast on the alien corpus.
- Stage 4: An online container.
The files you get
- Yours to edit: container.py.
- Read-only: bench.py, tests/__init__.py.
- Data: data/medium.txt, data/alien.txt.
- Tests you can read and run: tests/test_part1_brute_force.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 Word Container: Words Inside Words 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?
Meta. It is modelled on Meta's round: CoderPad with integrated AI assistant (GPT-4o mini, Claude Sonnet/Haiku, Gemini 2.5 Pro, Llama 4).
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 Meta runs its AI round, the AI coding interview guide.